High Major Histocompatibility Complex Class Research Articles

Tumor-associated NK cells drive MDSC-mediated tumor immune tolerance through the IL-6/STAT3 axis.

Apart from their killer identity, natural killer (NK) cells have integral roles in shaping the tumor microenvironment. Through immune gene deconvolution, the present study revealed an interplay between NK cells and myeloid-derived suppressor cells (MDSCs) in nonresponders of immune checkpoint therapy. Given that the mechanisms governing the outcome of NK cell-to-myeloid cell interactions remain largely unknown, we sought to investigate the cross-talk between NK cells and suppressive myeloid cells. Upon contact with tumor-experienced NK cells, monocytes and neutrophils displayed increased expression of MDSC-related suppressive factors along with increased capacities to suppress T cells. These changes were accompanied by impaired antigen presentation by monocytes and increased ER stress response by neutrophils. In a cohort of patients with sarcoma and breast cancer, the production of interleukin-6 (IL-6) by tumor-infiltrating NK cells correlated with S100A8/9 and arginase-1 expression by MDSCs. At the same time, NK cell-derived IL-6 was associated with tumors with higher major histocompatibility complex class I expression, which we further validated with b2m-knockout (KO) tumor mice models. Similarly in syngeneic wild-type and IL-6 KO mouse models, we then demonstrated that the accumulation of MDSCs was influenced by the presence of such regulatory NK cells. Inhibition of the IL-6/signal transducer and activator of transcription 3 (STAT3) axis alleviated suppression of T cell responses, resulting in reduced tumor growth and metastatic dissemination. Together, these results characterize a critical NK cell-mediated mechanism that drives the development of MDSCs during tumor immune escape.

Genetic Deletion of Galectin-3 Inhibits Pancreatic Cancer Progression and Enhances the Efficacy of Immunotherapy

BACKGROUND & AIMSPancreatic ductal adenocarcinoma (PDAC) has a desmoplastic tumor stroma and immunosuppressive microenvironment. Galectin-3 (GAL3) is enriched in PDAC, highly expressed by cancer cells and myeloid cells. However, the functional roles of GAL3 in the PDAC microenvironment remain elusive. METHODSWe generated a novel transgenic mouse model (KPPC;Lgals3-/-) that allows the genetic depletion of GAL3 from both cancer cells and myeloid cells in spontaneous PDAC formation. Single-cell RNA-sequencing analysis was used to identify the alterations in the tumor microenvironment upon GAL3 depletion. We investigated both the cancer cell-intrinsic function and immunosuppressive function of GAL3. We also evaluated the therapeutic efficacy of GAL3 inhibition in combination with immunotherapy. RESULTSGenetic deletion of GAL3 significantly inhibited the spontaneous pancreatic tumor progression and prolonged the survival of KPPC;Lgals3-/- mice. Single-cell analysis revealed that genetic deletion of GAL3 altered the phenotypes of immune cells, cancer cells, and other cell populations. GAL3 deletion significantly enriched the anti-tumor myeloid cell subpopulation with high major histocompatibility complex class II (MHCII) expression. We also identified that GAL3 depletion resulted in CXCL12 upregulation, which could act as a potential compensating mechanism upon GAL3 deficiency. Combined inhibition of CXCL12-CXCR4 axis and GAL3 enhanced the efficacy of anti-PD-1 immunotherapy, leading to significantly inhibited PDAC progression. In addition, deletion of GAL3 also inhibited the basal/mesenchymal-like phenotype of pancreatic cancer cells. CONCLUSIONSGAL3 promotes PDAC progression and immunosuppression via both cancer cell-intrinsic and immune-related mechanisms. Combined treatment targeting GAL3, CXCL12-CXCR4 axis, and PD-1 represents a novel therapeutic strategy for PDAC.

A clinical trial of therapeutic vaccination in lymphoma with serial tumor sampling and single-cell analysis

AbstractIn situ vaccination (ISV) triggers an immune response to tumor-associated antigens at 1 tumor site, which can then tackle the disease throughout the body. Here, we report clinical and biological results of a phase 1/2 ISV trial in patients with low-grade lymphoma, combining an intratumoral toll-like receptor 9 (TLR9) agonist with local low-dose radiation and ibrutinib (an inhibitor of B- and T-cell kinases). Adverse events were predominately low grade. The overall response rate was 50%, including 1 complete response. All patients experienced tumor reduction at distant sites. Single-cell analyses of serial fine needle aspirates from injected and uninjected tumors revealed correlates of clinical response, such as lower CD47 and higher major histocompatibility complex class II expression on tumor cells, enhanced T-cell and natural killer cell effector function, and reduced immune suppression from transforming growth factor β and inhibitory T regulatory 1 cells. Although changes at the local injected site were more pronounced, changes at distant uninjected sites were more often associated with clinical responses. Functional immune response assays and tracking of T-cell receptor sequences provided evidence of treatment-induced tumor-specific T-cell responses. Induction of immune effectors and reversal of negative regulators were both important in producing clinically meaningful tumor responses. The trial was registered at www.clinicaltrials.gov as #NCT02927964.

Abstract 707: High major histocompatibility complex class I expression overcomes cancer immunotherapy resistance due to interferon gamma signaling pathway defects

Abstract IFN-γ signaling pathway defects such as JAK mutations are well-known mechanisms of resistance to immune checkpoint inhibitors (ICIs). However, some patients respond to ICIs despite IFN-γ signaling pathway defects, and the detailed mechanisms remain unclear. Here, we created JAK-deleted cancer cell lines and evaluated antitumor immunity. As a result, several tumors responded to PD-1 blockade despite JAK deletion. Such sensitive tumors had high major histocompatibility complex class I (MHC-I) expression despite IFN-γ signaling pathway defects, whereas MHC-I expression was reduced by JAK deletion in resistant tumors. In particular, if cancer cells had high MHC-I expression despite defects in IFN-γ signaling pathways, chemokines that recruit effector T cells were mainly produced by immune cells rather than cancer cells in the tumor microenvironment. Accordingly, we found a response to ICIs in a patient with JAK-negative head and neck squamous cell carcinoma, whose human leukocyte antigen class I (HLA-I) expression level was maintained. In addition, clustered regularly interspaced short palindromic repeats (CRISPR) screening to identify molecules with elevated MHC-I expression independent of IFN-γ signaling pathways demonstrated that guanine nucleotide-binding protein subunit gamma 4 (GNG4) maintained MHC-I expression via the NF-κB signaling pathway. Our results indicate that patients with IFN-ɤ signaling pathway defects are not always resistant to ICIs, and highlight the importance of MHC-I expression among the pathways, including inhibitory effects on cellular proliferation or chemokine production, and the possibility of NF-κB-targeted therapies to overcome such resistance. Citation Format: Katsushige Kawase, Shusuke Kawashima, Joji Nagasaki, Takashi Inozume, Hiromasa Yamamoto, Masahito Kawazu, Toyoyuki Hanazawa, Yosuke Togashi. High major histocompatibility complex class I expression overcomes cancer immunotherapy resistance due to interferon gamma signaling pathway defects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 707.

Abstract 3514: Bispecific gamma delta T cell engagers containing butyrophilin 2A1/3A1 heterodimeric fusion protein efficiently activate Vg9Vd2 T cells and promote tumor cell killing

Abstract A primary mechanism of cancer immunotherapy resistance involves downregulation of specific antigens or major histocompatibility complex (MHC) based antigen presentation, which renders tumor cells invisible to αβ T cells, but not γδ T cells. Recently, a two-step model of γδ T cell activation has emerged, wherein one butyrophilin (BTN, i.e., BTN2A1) directly binds the γδ TCR but is only activated if certain molecular patterns (e.g., phosphoantigens) facilitate recruitment of a second BTN (i.e., BTN3A1) into a complex to form a BTN2A1/3A1 heterodimer. The BTN2A1/3A1 complex specifically activates the Vγ9Vδ2 T cells found in the peripheral blood in response to phosphoantigen build up in tumor cells. The unique mechanism of action and specificity of γδ TCR/BTN interactions suggests that therapeutic proteins comprising specific BTN heterodimers could be used to target specific γδ T cell populations to tumor cells which lack expression of high affinity neoantigens or MHC class I molecules. In this study, we generated bispecific γδ T cell engagers (GADLEN) containing heterodimeric BTN2A1 and BTN3A1 extracellular domains (ECD) fused via inert Fc linkers to scFv domains targeting a tumor-antigen (CD19 or CD33) to test their ability to modulate Vγ9Vδ2 T cells and to promote tumor cell killing in co-culture assays. GADLEN induced proliferation, degranulation and cytokine production including IFNγ and TNFα in Vγ9Vδ2 T cells but requires co-stimulation of a natural cytotoxicity receptor (via anti-NKG2D) or T-cell co-stimulatory receptor (via anti-CD28), highlighting the parallels of signal 1 and signal 2 requirements of TCR activation in αβ- and γδ- T cells. In Vγ9Vδ2 T cells and tumor co-culture assays, the addition of GADLEN alone enhanced killing of CD19+ lymphoma cells such as Daudi and Raji, expressing known ligands for CD28 (e.g., CD80 and CD86). Similarly, GADLEN enhanced Vγ9Vδ2 T cell-mediated killing of K562 cells engineered to express CD19, which express MICA/B (ligands for NKG2D) on the cell surface. In addition, the CD33-targeted GADLEN alone was able to specifically kill acute myeloid leukemia cells expressing CD33 and costimulatory ligands (e.g., CD80 and CD86) in a mechanism similar to the CD19-targeted GADLEN construct. These results highlight the ability of GADLENs in promoting targeted killing of tumor cells by providing the “active” heterodimeric BTN2A1 and BTN3A1 that is critical to enhance cytotoxic killing by Vγ9Vδ2 T cells. Furthermore, this study provides mechanistic insights into BTN-mediated activation of Vγ9Vδ2 T cells and offers proof of concept for using antigen-targeted butyrophilin heterodimeric fusion proteins for the treatment of cancer. Citation Format: Anne Lai, Arpita Patel, Faraha Brewer, Kinsley Evans, Kellsey Johannes, Louis Gonzalez, Kyung Jin Yoo, George Fromm, Keith Wilson, Taylor H. Schreiber, Suresh de Silva. Bispecific gamma delta T cell engagers containing butyrophilin 2A1/3A1 heterodimeric fusion protein efficiently activate Vg9Vd2 T cells and promote tumor cell killing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3514.

Unravelling the sex-specific diversity and functions of adrenal gland macrophages.

SummaryDespite the ubiquitous function of macrophages across the body, the diversity, origin, and function of adrenal gland macrophages remain largely unknown. We define the heterogeneity of adrenal gland immune cells using single-cell RNA sequencing and use genetic models to explore the developmental mechanisms yielding macrophage diversity. We define populations of monocyte-derived and embryonically seeded adrenal gland macrophages and identify a female-specific subset with low major histocompatibility complex (MHC) class II expression. In adulthood, monocyte recruitment dominates adrenal gland macrophage maintenance in female mice. Adrenal gland macrophage sub-tissular distribution follows a sex-dimorphic pattern, with MHC class IIlow macrophages located at the cortico-medullary junction. Macrophage sex dimorphism depends on the presence of the cortical X-zone. Adrenal gland macrophage depletion results in altered tissue homeostasis, modulated lipid metabolism, and decreased local aldosterone production during stress exposure. Overall, these data reveal the heterogeneity of adrenal gland macrophages and point toward sex-restricted distribution and functions of these cells.

Influence of T Cell-Mediated Immune Surveillance on Somatic Mutation Occurrences in Melanoma.

BackgroundNeoantigens are presented on the cancer cell surface by peptide-restricted human leukocyte antigen (HLA) proteins and can subsequently activate cognate T cells. It has been hypothesized that the observed somatic mutations in tumors are shaped by immunosurveillance.MethodsWe investigated all somatic mutations identified in The Cancer Genome Atlas (TCGA) Skin Cutaneous Melanoma (SKCM) samples. By applying a computational algorithm, we calculated the binding affinity of the resulting neo-peptides and their corresponding wild-type peptides with the major histocompatibility complex (MHC) Class I complex. We then examined the relationship between binding affinity alterations and mutation frequency.ResultsOur results show that neoantigens derived from recurrent mutations tend to have lower binding affinities with the MHC Class I complex compared to peptides from non-recurrent mutations. Tumor samples harboring recurrent SKCM mutations exhibited lower immune infiltration levels, indicating a relatively colder immune microenvironment.ConclusionsThese results suggested that the occurrences of somatic mutations in melanoma have been shaped by immunosurveillance. Mutations that lead to neoantigens with high MHC class I binding affinity are more likely to be eliminated and thus are less likely to be present in tumors.

Updated Overall Survival Data and Predictive Biomarkers of Sintilimab Plus Pemetrexed and Platinum as First-Line Treatment for Locally Advanced or Metastatic Nonsquamous NSCLC in the Phase 3 ORIENT-11 Study

IntroductionSintilimab plus chemotherapy significantly prolonged progression-free survival (PFS) compared with chemotherapy alone in nonsquamous NSCLC in the ORIENT-11 study. Updated overall survival (OS) and PFS data and corresponding biomarker analyses are reported here. MethodsIn this study, a total of 397 patients with previously untreated, locally advanced or metastatic nonsquamous NSCLC were assigned to sintilimab plus chemotherapy combination treatment (combo) group or placebo plus chemotherapy treatment group. The patients were stratified by programmed death-ligand 1 (PD-L1) expression levels. Immune signature profiles from tumor RNA sequencing and PD-L1 immunohistochemistry were correlated with clinical outcome to identify predictive biomarkers. ResultsAs of January 2021, with median follow-up of 22.9 months, median OS was significantly improved in the combo group compared with the placebo plus chemotherapy treatment group (not reached versus 16.8 mo; hazard ratio [HR] = 0.60, 95% confidence interval [CI]: 0.45–0.79, p = 0.0003). High or medium immune cell infiltration was strongly associated with improved PFS in the combo group, in contrast to absent or low immune cell infiltration, which suggests that chemotherapy could not prime “immune deserts” to obtain benefit from programmed cell death protein-1 inhibition. In particular, high major histocompatibility complex (MHC) class II presentation pathway expression was significantly correlated with prolonged PFS (HR = 0.32, 95% CI: 0.19–0.54, p < 0.0001) and OS (HR = 0.36, 95% CI: 0.20–0.64, p = 0.0005) in the combo group. Importantly, patients with low or absent PD-L1 but high MHC class II expression could still benefit from the combo treatment. In contrast, MHC class I antigen presentation pathway was less relevant in this combination setting. ConclusionsThe addition of sintilimab to chemotherapy resulted to significantly longer OS in nonsquamous NSCLC. Expression of MHC class II antigen presentation pathway could identify patients benefiting most from this combination.

Sex-Specific Effects of Microglia-Like Cell Engraftment during Experimental Autoimmune Encephalomyelitis.

Multiple sclerosis (MS) is a chronic neuroinflammatory disorder of the central nervous system (CNS) that usually presents in young adults and predominantly in females. Microglia, a major resident immune cell in the CNS, are critical players in both CNS homeostasis and disease. We have previously demonstrated that microglia can be efficiently depleted by the administration of tamoxifen in Cx3cr1CreER/+Rosa26DTA/+ mice, with ensuing repopulation deriving from both the proliferation of residual CNS resident microglia and the engraftment of peripheral monocyte-derived microglia-like cells. In this study, tamoxifen was administered to Cx3cr1CreER/+Rosa26DTA/+ and Cx3cr1CreER/+ female and male mice. Experimental autoimmune encephalomyelitis (EAE), a widely used animal model of MS, was induced by active immunization with myelin oligodendrocyte glycoprotein (MOG) one month after tamoxifen injections in Cx3cr1CreER/+Rosa26DTA/+ mice and Cx3cr1CreER/+ mice, a time point when the CNS niche was colonized by microglia derived from both CNS microglia and peripherally-derived macrophages. We demonstrate that engraftment of microglia-like cells following microglial depletion exacerbated EAE in Cx3cr1CreER/+Rosa26DTA/+ female mice as assessed by clinical symptoms and the expression of CNS inflammatory factors, but these findings were not evident in male mice. Higher major histocompatibility complex class II expression and cytokine production in the female CNS contributed to the sex-dependent EAE severity in mice following engraftment of microglia-like cells. An underestimated yet marked sex-dependent microglial activation pattern may exist in the injured CNS during EAE.

Avelumab in patients with previously treated metastatic Merkel cell carcinoma: long-term data and biomarker analyses from the single-arm phase 2 JAVELIN Merkel 200 trial

BackgroundMerkel cell carcinoma (MCC) is a rare, aggressive skin cancer associated with a high risk of metastasis. In 2017, avelumab (anti–programmed death-ligand 1 (PD-L1)) became the first approved treatment for...

Can extreme MHC class I diversity be a feature of a wide geographic range? The example of Seba's short-tailed bat (Carollia perspicillata).

The major histocompatibility complex (MHC) is one of the most diverse genetic regions under pathogen-driven selection because of its central role in antigen binding and immunity. The highest MHC variability, both in terms of the number of individual alleles and gene copies, has so far been found in passerine birds; this is probably attributable to passerine adaptation to both a wide geographic range and a diverse array of habitats. If extraordinary high MHC variation and duplication rates are adaptive features under selection during the evolution of ecologically and taxonomically diverse species, then similarly diverse MHC architectures should be found in bats. Bats are an extremely species-rich mammalian group that is globally widely distributed. Many bat species roost in multitudinous groups and have high contact rates with pathogens, conspecifics, and allospecifics. We have characterized the MHC class I diversity in 116 Panamanian Seba’s short-tailed bats (Carollia perspicillata), a widely distributed, generalist, neotropical species. We have detected a remarkable individual and population-level diversity of MHC class I genes, with between seven and 22 alleles and a unique genotype in each individual. This diversity is comparable with that reported in passerine birds and, in both taxonomic groups, further variability has evolved through length polymorphisms. Our findings support the hypothesis that, for species with a geographically broader range, high MHC class I variability is particularly adaptive. Investigation of the details of the underlying adaptive processes and the role of the high MHC diversity in pathogen resistance are important next steps for a better understanding of the role of bats in viral evolution and as carriers of several deadly zoonotic viruses.Electronic supplementary materialThe online version of this article (10.1007/s00251-019-01128-7) contains supplementary material, which is available to authorized users.

Blood parasites shape extreme major histocompatibility complex diversity in a migratory passerine.

Pathogens are one of the main forces driving the evolution and maintenance of the highly polymorphic genes of the vertebrate major histocompatibility complex (MHC). Although MHC proteins are crucial in pathogen recognition, it is still poorly understood how pathogen-mediated selection promotes and maintains MHC diversity, and especially so in host species with highly duplicated MHC genes. Sedge warblers (Acrocephalus schoenobaenus) have highly duplicated MHC genes, and using data from high-throughput MHC genotyping, we were able to investigate to what extent avian malaria parasites explain temporal MHC class I supertype fluctuations in a long-term study population. We investigated infection status and infection intensities of two different strains of Haemoproteus, that is avian malaria parasites that are known to have significant fitness consequences in sedge warblers. We found that prevalence of avian malaria in carriers of specific MHC class I supertypes was a significant predictor of their frequency changes between years. This finding suggests that avian malaria infections partly drive the temporal fluctuations of the MHC class I supertypes. Furthermore, we found that individuals with a large number of different supertypes had higher resistance to avian malaria, but there was no evidence for an optimal MHC class I diversity. Thus, the two studied malaria parasite strains appear to select for a high MHC class I supertype diversity. Such selection may explain the maintenance of the extremely high number of MHC class I gene copies in sedge warblers and possibly also in other passerines where avian malaria is a common disease.

The evolution of immunity in relation to colonization and migration.

Colonization and migration have a crucial effect on patterns of biodiversity, with disease predicted to play an important role in these processes. However, evidence of the effect of pathogens on broad patterns of colonization and migration is limited. Here, using phylogenetic analyses of 1,311 species of Afro-Palaearctic songbirds, we show that colonization events from regions of high (sub-Saharan Africa) to low (the Palaearctic) pathogen diversity were up to 20 times more frequent than the reverse, and that migration has evolved 3 times more frequently from African- as opposed to Palaearctic-resident species. We also found that resident species that colonized the Palaearctic from Africa, as well as African species that evolved long-distance migration to breed in the Palaearctic, have reduced diversity of key immune genes associated with pathogen recognition (major histocompatibility complex class I). These results suggest that changes in the pathogen community that occur during colonization and migration shape the evolution of the immune system, potentially by adjusting the trade-off between the benefits of extensive pathogen recognition and the costs of immunopathology that result from high major histocompatibility complex class I diversity.

PD57-08 TUMORAL CD8+ T CELLS CORRELATE WITH FAVORABLE OUTCOME IN METASTATIC RENAL CELL CARCINOMA TREATED WITH TYROSINE KINASE INHIBITORS

You have accessJournal of UrologyKidney Cancer: Advanced (including Drug Therapy) III1 Apr 2018PD57-08 TUMORAL CD8+ T CELLS CORRELATE WITH FAVORABLE OUTCOME IN METASTATIC RENAL CELL CARCINOMA TREATED WITH TYROSINE KINASE INHIBITORS Jiajun Wang, Li Liu, Wei Xi, Jiejie Xu, and Jianming Guo Jiajun WangJiajun Wang More articles by this author , Li LiuLi Liu More articles by this author , Wei XiWei Xi More articles by this author , Jiejie XuJiejie Xu More articles by this author , and Jianming GuoJianming Guo More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.2652AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES CD8+ T cells play a central role in cancer immune elimination, and tyrosine kinase inhibitor (TKI) therapy could enhance their anti-tumor function. We aim to investigate the predictive value of CD8+ T cells for TKI therapy in metastatic renal cell carcinoma (mRCC) patients. METHODS One hundred and thirty-eight metastatic mRCC patients treated with TKIs were retrospectively scanned, and 111 eligible patients were finally enrolled. CD8+ T cell density and major histocompatibility complex (MHC) class I expression in tumor tissues was assessed by immunohistochemistry. Associations between CD8+ T cell density, MHC class I expression and local immune cytolytic activity were also assessed in the TCGA cohort. RESULTS CD8+ T cells were observed in mRCC samples (median density 45 cells/mm2, range 0-2750 cells/mm2). Patients with high density of CD8+ T cells showed higher response rate (P=0.002), longer overall survival (OS) (hazard ratio=0.510, P=0.005) and longer progression-free survival (PFS) (hazard ratio=0.591, P=0.012) under TKI therapy. Multivariate Cox analyses identified high CD8+ T cell density as an independent prognostic factor for both OS (hazard ratio=0.559, P=0.027) and PFS (hazard ratio=0.574, P=0.017). We also identified close relationship between high CD8+ T cell infiltration, activated antigen presentation mechanism and enhanced immune cytolytic activity. Moreover, mRCC patients with both high tumoral CD8+ T cell density and high MHC class I expression showed significantly prolonged survival (P<10-4). CONCLUSIONS Tumoral CD8+ T cell density could serve as a predictive marker for TKI therapy in mRCC patients, especially in those with high MHC class I expression. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e1069-e1070 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Jiajun Wang More articles by this author Li Liu More articles by this author Wei Xi More articles by this author Jiejie Xu More articles by this author Jianming Guo More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Very high MHC Class IIB diversity without spatial differentiation in the mediterranean population of greater Flamingos

BackgroundSelective pressure from pathogens is thought to shape the allelic diversity of major histocompatibility complex (MHC) genes in vertebrates. In particular, both local adaptation to pathogens and gene flow are thought to explain a large part of the intraspecific variation observed in MHC allelic diversity. To date, however, evidence that adaptation to locally prevalent pathogens maintains MHC variation is limited to species with limited dispersal and, hence, reduced gene flow. On the one hand high gene flow can disrupt local adaptation in species with high dispersal rates, on the other hand such species are much more likely to experience spatial variation in pathogen pressure, suggesting that there may be intense pathogen mediated selection pressure operating across breeding sites in panmictic species. Such pathogen mediated selection pressure operating across breeding sites should therefore be sufficient to maintain high MHC diversity in high dispersing species in the absence of local adaptation mechanisms. We used the Greater Flamingo, Phoenicopterus roseus, a long-lived colonial bird showing a homogeneous genetic structure of neutral markers at the scale of the Mediterranean region, to test the prediction that higher MHC allelic diversity with no population structure should occur in large panmictic populations of long-distance dispersing birds than in other resident species.ResultsWe assessed the level of allelic diversity at the MHC Class IIB exon 2 from 116 individuals born in four different breeding colonies of Greater Flamingo in the Mediterranean region. We found one of the highest allelic diversity (109 alleles, 2 loci) of any non-passerine avian species investigated so far relative to the number of individuals and loci genotyped. There was no evidence of population structure between the four major Mediterranean breeding colonies.ConclusionOur results suggest that local adaptation at MHC Class IIB in Greater Flamingos is constrained by high gene flow and high MHC diversity appears to be maintained by population wide pathogen-mediated selection rather than local pathogen-mediated selection. Further understanding of how pathogens vary across space and time will be crucial to further elucidate the mechanisms maintaining MHC diversity in species with large panmictic populations and high dispersal rates.

Characterization of MHC class IA in the endangered southern corroboree frog

Southern corroboree frogs (Pseudophryne corroboree) have declined to near extinction in the wild after the emergence of the amphibian chytrid fungus Batrachochytrium dendrobatidis in southeastern Australia in the 1980s. A major captive breeding and reintroduction program is underway to preserve this iconic species, but improving resistance to B. dendrobatidis would help the wild population to be self-sustaining. Using 3' and 5' rapid amplification of complementary DNA ends (RACE), we characterized the major histocompatibility complex (MHC) class IA locus in this species. We then used sequences generated from RACE to design primers to amplify the peptide-binding region (PBR) of this functional genetic marker. Finally, we analysed the diversity, phylogeny, and selection patterns of PBR sequences from four P. corroboree populations and compared this with other amphibian species. We found moderately high MHC class IA genetic diversity in this species and evidence of strong positive and purifying selection at sites that are associated with putative PBR pockets in other species, indicating that this gene region may be under selection for resistance to Bd. Future studies should focus on identifying alleles associated with Bd resistance in P. corroboree by performing a Bd laboratory challenge study to confirm the functional importance of our genetic findings and explore their use in artificial selection or genetic engineering to increase resistance to chytridiomycosis.

High major histocompatibility complex class I polymorphism despite bottlenecks in wild and domesticated populations of the zebra finch (Taeniopygia guttata).

BackgroundTwo subspecies of zebra finch, Taeniopygia guttata castanotis and T. g. guttata are native to Australia and the Lesser Sunda Islands, respectively. The Australian subspecies has been domesticated and is now an important model system for research. Both the Lesser Sundan subspecies and domesticated Australian zebra finches have undergone population bottlenecks in their history, and previous analyses using neutral markers have reported reduced neutral genetic diversity in these populations. Here we characterize patterns of variation in the third exon of the highly variable major histocompatibility complex (MHC) class I α chain. As a benchmark for neutral divergence, we also report the first mitochondrial NADH dehydrogenase 2 (ND2) sequences in this important model system.ResultsDespite natural and human-mediated population bottlenecks, we find that high MHC class I polymorphism persists across all populations. As expected, we find higher levels of nucleotide diversity in the MHC locus relative to neutral loci, and strong evidence of positive selection acting on important residues forming the peptide-binding region (PBR). Clear population differentiation of MHC allele frequencies is also evident, and this may be due to adaptation to new habitats and associated pathogens and/or genetic drift. Whereas the MHC Class I locus shows broad haplotype sharing across populations, ND2 is the first locus surveyed to date to show reciprocal monophyly of the two subspecies.ConclusionsDespite genetic bottlenecks and genetic drift, all surveyed zebra finch populations have maintained high MHC Class I diversity. The diversity at the MHC Class I locus in the Lesser Sundan subspecies contrasts sharply with the lack of diversity in previously examined neutral loci, and may thus be a result of selection acting to maintain polymorphism. Given uncertainty in historical population demography, however, it is difficult to rule out neutral processes in maintaining the observed diversity. The surveyed populations also differ in MHC Class I allele frequencies, and future studies are needed to assess whether these changes result in functional immune differences.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0546-3) contains supplementary material, which is available to authorized users.

Behavioural and genetic analyses of mate choice and reproductive success in two Chinook salmon populations

Sexual selection is recognized as an important evolutionary force in salmon. However, relatively little is known about variation in sexual selection pressures across salmon populations or the potential role of natural selection as a driver of adaptive mating patterns. Here, we examine mating behaviour and correlates of reproductive success in Chinook salmon (Oncorhynchus tshawytscha) from the Quinsam and Little Qualicum rivers in British Columbia, Canada — two populations for which we have previously found evidence of natural selection operating on major histocompatibility complex (MHC) genes. In both populations, males courted females and exhibited dominance behaviour towards other males, and the frequency of each behaviour was positively associated with reproductive success. Males were more aggressive towards females with whom they would produce offspring of low or high MHC class II diversity, and the offspring of males from the Quinsam River exhibited higher diversity at the MHC class I than expected. We discuss our results in relation to local natural selection pressures on the MHC and the potential for MHC-dependent mate choice.

Extremely high major histocompatibility complex class IIb gene intron 2 variation and population structure in Chinese alligator

Identifying the processes that maintain genetic diversity within and among populations is a central goal of modern evolutionary genetics. So far, the studies on genetic diversity have mainly focussed on neutral DNA markers, such as mtDNA and microsatellites (Xu et al. 2010). While these markers are very informative in molecular clocks, to examine dispersal patterns of individuals (gene flow) and to classify them by relatedness and paternity analyses. The variation at neutral loci cannot provide direct information on selective processes involving the interaction of individuals with their environment or on the capacity for future adaptive changes (Sommer 2005). With the developments in molecular biology, researchers can directly examine selection at genes that underlie functional traits. Therefore, adaptive nonneutral markers have become especially valuable (Koskinen et al. 2002). One important example comes from the genes of the major histocompatibility complex (MHC). These genes are found in all jawed vertebrates and play a critical role in an organism’s immune response (Karaiskou et al. 2010). High levels of variation in MHC alleles are believed to confer the ability to recognize a wide range of antigens and thus increase resistance to a greater number of environmental pathogens. Chinese alligator (Alligator sinensis) is one of the 23 critically endangered crocodile species in the world. The wild population has been close to extinct during the past decades due to habitat loss and illegal hunting. The investigation indicated that the number of wild Chinese alligators has decreased from 500 individuals in the 1980s to currently less than 120 or 150 individuals (Thorbjarnarson et al. 2002).

Iodide, cytokines and TSH-receptor expression in Graves' disease.

The present study was initiated to characterize thyrotropin receptor (TSH-R) expression in thyroids from patients with Graves' disease, as well as parameters that influence TSH-R expression either causally, such as interferon-gamma (IFN-gamma), the leading candidate among the cytokines thought to play a key role in the initiation of autoimmune thyroid disease, or therapeutically, such as iodide, which is used to prepare patients for surgery. Our data show that there is an average 4-fold increase of TSH-R mRNA levels in the thyroids of Graves' patients coming to surgery, which is paralleled by an increase in TSH-R protein levels and TSH binding capacity. The increase does not appear to be related to IFN-gamma since IFN-gamma transcripts are barely detectable in most Graves' patients. Iodide treatment causes a 2-fold decrease in TSH-R expression in association with significant decreases in major histocompatibility complex (MHC) class I and class II gene expression. These last data are compatible with a recently enunciated "transcription factor hypothesis" according to which abnormally high TSH-R and MHC class I and class II gene expression in Graves' thyroids are the result of a loss of the normal negative regulation of these genes necessary to allow the normal growth and function of the gland, yet preserve self-tolerance.