Thymic Cortex Research Articles

Dynamics of the thymic transcriptome at stages of acute thymic involution in Japanese Black calves with a poor prognosis

Transcriptome analysis was performed on the thymus of Japanese Black calves that were necropsied due to poor prognosis, to characterize changes associated with acute thymic involution. Gene expression profiles obtained by DNA microarray analysis of eight calf thymuses were classified into three patterns that correlated with the histopathological stage of acute thymic involution. Using principal component analysis, the first principal component of the global gene expression levels in the calf thymus was associated with the stage of acute thymic involution, suggesting that histopathological changes greatly influence the gene expression profile. Gene ontology enrichment analysis revealed that genes related to cell proliferation, wound healing, and inflammatory responses were the main contributors to the first principal component. Real-time RT-PCR showed that the thymus had lower expression of PCNA, KIFC1, and HES6, and higher expression of SYNPO2, PDGFRB, and TWIST1 during acute thymic involution. Immunohistochemistry demonstrated a decrease in the rate of Ki67-positive cells in the thymic cortex during the late stage of acute thymic involution. The rate of cleaved caspase-1-positive cells increased in the thymic cortex at an earlier stage than the increase in the rate of cleaved caspase-3-positive cells. Vimentin, which was almost absent in the non-involuted thymic cortex, appeared in the thymic cortex during acute thymic involution. These results suggest that in farmed calves with a poor prognosis, inflammatory responses and impaired thymocyte proliferation are primarily involved in acute thymic involution.

Preparation of Single-cell Suspension of Mouse Thymic Epithelial Cells and Staining of Intracellular Molecules for Flow Cytometric Analysis.

Thymic epithelial cells (TECs) play an essential role in promoting the development and repertoire selection of T cells. Cortical TECs (cTECs) in the thymic cortex induce early T cell development and positive selection of cortical thymocytes. In contrast, medullary TECs (mTECs) in the thymic medulla attract positively selected thymocytes from the cortex and establish self-tolerance in T cells. A variety of molecules, including DLL4 and beta5t expressed in cTECs, as well as Aire and CCL21 expressed in mTECs, contribute to thymus function supporting T cell development and selection. Flow cytometric analysis of functionally relevant molecules in cTECs and mTECs is useful to improve our understanding of the biology of TECs, even though current methods for the preparation of single-cell suspensions of TECs can retrieve only a small fraction of TECs (approximately 1% for cTECs and approximately 10% for mTECs) from young adult mouse thymus. Because many of these functionally relevant molecules in TECs are localized within the cells, we describe our protocols for the preparation of single-cell suspension of mouse TECs and the staining of intracellular molecules for flow cytometric analysis.

Characterization of thymic architecture and lymphocyte populations in X-MAID due to an underlying pathogenic moesin mutation

Background: X-linked Moesin Associated Immunodeficiency (X-MAID) is a combined immunodeficiency caused by deficiency in the moesin protein. Moesin, which is encoded by the MSN gene, is part of the ezrin-radixin-moesin (ERM) family of transmembrane proteins that interact with the actin cytoskeleton and regulate the shape and migration of cells. Deficiency of moesin is associated with aberrant T cell migration and inadequate immune synapse formation, leading to significant immunodeficiency and recurrent infections. While the clinical presentation of X-MAID is diverse, to date, no thymus histopathology findings have been reported. Aim: Describe the thymus histopathology of a patient with X-MAID. Results: Our patient is a 10-year-old male who presented early in life with recurrent infections, dysmorphic features, and severe pulmonary venous stenosis which required a double lung transplant at the age of 4 years. Prior to transplant, he was referred to Immunology for assessment and was subsequently found to harbour a hemizygous variant in the MSN gene (c.278dupT; p.L93FfsX21). Thymus histopathology findings showed significant cortical atrophy and dysplasia and was accompanied by reduction in CD3+ cells in the cortex. Abnormally low numbers of suppressor T cells and T helper cells in the thymic cortex and medulla were noted. Conclusion: Thymic findings in X-MAID can include cortical atrophy, dysplasia, and decreased cellularity. This provides further evidence for the importance of moesin on T cell development and migration in the thymus. Statement of novelty: Description of thymus histopathology in a patient with X-MAID.

Sulforaphane Ameliorate Cadmium-Induced Blood-Thymus Barrier Disruption by Targeting the PI3K/AKT/FOXO1 Axis.

Cadmium (Cd) is a transition metal ion that is extremely harmful to human and animal biological systems. Cd is a toxic substance that can accumulate in the food chain and cause various health issues. Sulforaphane (SFN) is a natural bioactive compound with potent antioxidant properties. In our study, 80 1 day-old chicks were fed with Cd (140 mg/kg BW/day) and/or SFN (50 mg/kg BW/day) for 90 days. The blood-thymus barrier (BTB) is a selective barrier separating T-lymphocytes from blood and cortical capillaries in the thymus cortex. Our research revealed that Cd could destroy the BTB by downregulating Wnt/β-catenin signaling and induce immunodeficiency, leading to irreversible injury to the immune system. The study emphasizes the health benefits of SFN in the thymus. SFN could ameliorate Cd-triggered BTB dysfunction and pyroptosis in the thymus tissues. SFN modulated the PI3K/AKT/FOXO1 axis, improving the level of claudin-5 (CLDN5) in the thymus to alleviate BTB breakdown. Our findings indicated the toxic impact of Cd on thymus, and BTB could be the specific target of Cd toxicity. The finding also provides evidence for the role of SFN in maintaining thymic homeostasis for Cd-related health issues.

Thymocyte migration and emigration

Hematopoietic precursors (HPCs) entering into the thymus undergo a sequential process leading to the generation of a variety of T cell subsets. This developmental odyssey unfolds in distinct stages within the thymic cortex and medulla, shaping the landscape of T cell receptor (TCR) expression and guiding thymocytes through positive and negative selection. Initially, early thymic progenitors (ETPs) take residence in the thymic cortex, where thymocytes begin to express their TCR and undergo positive selection. Subsequently, thymocytes transition to the thymic medulla, where they undergo negative selection. Both murine and human thymocyte development can be broadly classified into distinct stages based on the expression of CD4 and CD8 coreceptors, resulting in categorizations as double negative (DN), double positive (DP) or single positive (SP) cells. Thymocyte migration to the appropriate thymic microenvironment at the right differentiation stage is pivotal for the development and the proper functioning of T cells, which is critical for adaptive immune responses. The journey of lymphoid progenitor cells into the T cell developmental pathway hinges on an ongoing dialogue between the differentiating cell and the signals emanating from the thymus niche. Herein, we review the contribution of the key factors mentioned above for the localization, migration and emigration of thymocytes.

Morphofunctional features in mice treated by low and high Hsp70 doses

Aim. We sought to assess the effects of exogenous Hsp70 (single subcutaneous low- and high-dose injections) on organ structure and functions in adult mice.Materials and methods. We randomized CD1 90-day-old male mice (n = 30) to three groups (10 mice per group). We injected the animals with single subcutaneous saline solution for Group 1 (control), low dose (500 μg/kg) of recombinant human Hsp70 (HspA1A) for Group 2, and high dose (5000 μg/kg) of the Hsp70 for Group 3. We examined the behavior of the mice on Day 3 after the injections (distance traveled, velocity, and bowel movement number). We lethalized the mice on Day 5 with further histological study and morphometrics of cerebral cortex, thymus, spleen, and liver. The statistics included one-factor ANOVA test with post hoc Tukey test.Results. All study groups exhibited no significant difference of behavioral parameters. Some liver sinusoids were wider in control group and Hsp70 500 μg/kg group comparing to Hsp70 5000 μg/kg group. We obtained also data for morphometrics: no difference was found for the number of neurons in ganglionic cerebral cortex, the lymphocytic cellularity difference between thymic cortex and medulla, the number of lymphocytes in white splenic pulp, and the number of hepatocyte nuclei in the liver. Red splenic pulp exhibited 1774,5 ± 24,8, 1623,0 ± 26,7, 1553,6 ± 47,0 macrophages for control, low-dose and high-dose groups, respectively (р < 0,0001). Tukey test showed a significant difference between control group and each of Hsp70 groups 500 μg/kg (р = 0,012) and 5000 μg/kg (р < 0,0001).Conclusion. Our study revealed no negative impact of subcutaneous Hsp70 administration at low and high doses on organ structure and functions in mice.

Applications of EMbedding and backscattered scanning electron microscopy for morphological and functional assessment of the thymus forcedly removed in children with congenital heart defects during the first weeks of life

Thymectomy in a number of clinical situations is an unavoidable step of cardiac surgical treatment of congenital heart defects, but the issue of its effects on development of immunity in early ontogenesis remains open. There is still debates among scientists about the risk of immune deficiency states in children who underwent thymectomy at an early age. One may see completely different opinions, both in domestic and foreign publications. A tool for resolving this issue may be provided by morpho-functional studies of the removed thymic tissue by means of modern scanning electron microscopy techniques. The objective of our study was to assess the possibilities of EMbedding and backscattered scanning electron microscopy for morphological and functional evaluation of the thymus, which was forcedly removed in the infant patients with congenital heart defects over the first weeks of life. The thymus of a newborn infant (postnatal day 27) with congenital heart disease: ventricular septal defect was examined using EMbedding and backscattered scanning electron microscopy imaging after embedding in epoxy resin. The mass of thymus gland was 15.7 g, the dimensions of thymus were: transverse, 3.4 cm; longitudinal, 4.1 cm; thickness, 1.7 cm; volume, 12.4 cm3. The study showed ability of EMbedding and backscattered scanning electron microscopy in morphological and functional assessment of thymus gland considered the central organ of the immune system. Step-bystep visualization from low to high magnifications, from tissues to cells and intracellular structures, as well as layer-by-layer examination of thymic cortex, medulla, interlobular septa and vessels, allows you to effectively assess the functionality of the thymus. This research method is sufficient for scientific research of the forcedly removed thymus since it enables us to visualize its microanatomy, allowing cell phenotyping at different layers of the thymus, studying intercellular interactions of thymocytes with reticulo-epithelial cells, subtle features of Hassall’s bodies and, finally, the process of T lymphocytes’ release from thymus gland.

Thymic atrophy induced by Plasmodium berghei ANKA and Plasmodium yoelii 17XL infection

The thymus is the anatomical site where T cells undergo a complex process of differentiation, proliferation, selection, and elimination of autorreactive cells which involves molecular signals in different intrathymic environment. However, the immunological functions of the thymus can be compromised upon exposure to different infections, affecting thymocyte populations. In this work, we investigated the impact of malaria parasites on the thymus by using C57BL/6 mice infected with Plasmodium berghei ANKA and Plasmodium yoelii 17XL; these lethal infection models represent the most severe complications, cerebral malaria, and anemia respectively. Data showed a reduction in the thymic weight and cellularity involving different T cell maturation stages, mainly CD4−CD8− and CD4+CD8+ thymocytes, as well as an increased presence of apoptotic cells, leading to significant thymic cortex reduction. Thymus atrophy showed no association with elevated serum cytokines levels, although increased glucocorticoid levels did. The severity of thymic damage in both models reached the same extend although it occurs at different stages of infection, showing that thymic atrophy does not depend on parasitemia level but on the specific host-parasite interaction.

FRI564 Thymic Hyperplasia In Graves' Disease: An Under-recognized Association

Abstract Disclosure: S. Nachum: None. A. Rivadeneira: None. K.N. Kobaly: None. Association of thymic hyperplasia (TH) with Graves’ disease (GD) is rare and underrecognized. In an era of increased diagnostic imaging, incidental findings of thymic masses in patients with GD may be increasingly identified and awareness of this association may reduce unnecessary interventions. We report three cases of GD with TH at presentation, one of which includes resolution of TH. CASE 1: 56 year-old man with unintentional weight loss, palpitations and eye discomfort was diagnosed with GD (TSH <0.015, FT4 4.47, TRAB 8.18, TSI 8.51). He had an incidental 3x3 cm anterior mediastinal mass on a chest CT. MRI chest suggested TH. Myasthenia gravis antibodies were negative. I-123 uptake and scan showed diffusely increased uptake within the thyroid gland and no increased uptake in the upper chest corresponding to mediastinal mass. Initiation of methimazole normalized thyroid function. CT chest at 9 months showed near resolution of the anterior mediastinal soft tissue density compatible with resolving TH. CASE 2: 23 year-old woman presented with insomnia, palpitations, and neck pain and was found to have GD (TSH <0.01, FT4 2.75, TRAB 9.16, TSI 8.84). CT neck obtained due to pain showed diffuse enlargement of the thyroid and a soft tissue density in the partially imaged superior mediastinum. Methimazole was started. Further evaluation of mass is pending. CASE 3: 35 year-old man presented with atrial fibrillation and was diagnosed with hyperthyroidism (TSH < 0.01, FT4 5.55). Tc-99m pertechnetate scan showed diffuse uptake consistent with GD. Methimazole was started. CT chest obtained due to concern for pulmonary embolism showed a 12.6 x 3.0 cm anterior mediastinal mass. HCG was undetectable. Further evaluation of mass is pending. Discussion: TH is thought to occur due to hormonal excess stimulating the thymic cortex and immunological mechanisms that result in formation of medullary lymphoid follicles.1 The incidence of TH in GD is unknown as diagnostic imaging is not routinely obtained. A study of thymic biopsies in patients undergoing thyroidectomy found 38% of patients with thyrotoxicosis had histological evidence of TH.2 This benign condition improves with treatment of GD, with decreased thymic size after 5-24 months of treatment with antithyroid drugs.3 In the absence of a discrete mass, invasion of other tissues or calcifications, repeat imaging after 6 months with regression of TH by 50% obviates the need for biopsy.1 Biopsy and thymectomy should be deferred when thyrotoxic due to risk of precipitating thyroid storm4 and be reconsidered if thymus fails to regress on repeat imaging. Additional guidance for observation is needed as the differential diagnosis for mediastinal mass includes diseases warranting more urgent diagnosis and intervention. Identification of high-risk patient characteristics or imaging findings may be of clinical utility in this circumstance. Presentation: Friday, June 16, 2023

Immunohistochemical developmental comparative study between thymus and spleen of Peacock(Pavo Cristatus)

In thymus, CD8 showed -ve expression at one week age. At one and two months old, strongly +ve were observed within the thymic parenchyma and around Hassall's corpuscles. At seven months old, CD8 showed variable degrees of +ve expression especially around blood vessels but less frequency than that of the younger ages due to the retarded activity of the thymus gland. CD268 cells showed –ve expressions in cortex and medulla of thymus at the 1st week of age . At the age of one month old Peacock the CD268 exhibited high degree of +ve appearance for B cells. At the age of two months old, CD268 displayed +ve expression in thymic cortex particularly around the septae. At age of seven months old Peacocks, the adult cellular population were formed the whole parenchyma of thymus gland therefore CD268 give slightly +ve expression in the cortex mainly around the septae. While in the spleen, CD8 were showed –ve expression at the age of one week Peacock poult . At the age of (1,2 and 7) months old spleen have great role in the immunity. CD268 indicated –ve expressions at one week of age, because of most of the cells at this age immatured. Few numbers of B lymphocytes were showing +ve expression at one month of age .At age of two months old Peacock B cells showed highly +ve expression. At age of seven months old Peacocks showed +ve expression, and highly increase in the number of mature B lymphocytes compared with other previous younger ages

Aggregation-prone peptides from within a non-self-protein homoaggregate are preferred for MHC association: Historical overview.

New technologies assist re-evaluation of hypotheses on generation of immune cell repertoires and distinctions of self from non-self. Findings include positive correlations between peptide propensities to aggregate and their binding to major histocompatibility complex (MHC) proteins. This recalls the hypothesis that foreign proteins may homoaggregate in host cytosols prior to releasing their peptides (p) to form pMHC complexes. Clues to this included aggregation-related phenomena associated with infections (rouleaux formation, pyrexia, certain brain diseases). By virtue of 'promiscuous' gene expression by thymic presenting cells - perhaps adapted from earlier evolving gonadal mechanisms - developing T cells monitor surface pMHC clusterings. This evaluates intracellular concentrations of the corresponding proteins, and hence, following Burnet's two signal principle, degrees of self-reactivity. After positive selection in the thymic cortex for reactivity with 'near-self', high-level pMHC clustering suffices in the medulla for negatively selection. Following Burnet's principle, in the periphery low-level clustering suffices for T cell stimulation and high-level clustering again provokes negative selection (immunological tolerance). For evolving intracellular pathogens, fine-tuned polymorphisms of their host species have limited to 'near-self' some mimicking adaptations. It is proposed that while entire pathogen proteins may have evolved to minimize their aggregability, the greater aggregability of their peptides remains partially hidden within. Two-step proofreading mechanisms in prospective hosts select proteins containing aggregable peptide for the generation of pMHC clusters at the surface of presenting cells. Through mutations, some proteins of pathogens and cancer cells tend to converge towards the host 'near-self' that its T cells have auditioned to address.

Growth hormone enhances the CD34+ stem cells repopulation of the male albino rat thymus gland in cyclophosphamide induced injury: immunohistochemical and electron microscopic study

ABSTRACT Cyclophosphamide (CP) is a chemotherapeutic drug that has a harmful effect on the immune system. Growth hormone (GH) is a peptide hormone that can enhance thymic functions in cases of immunosuppression. Therefore, the present study was performed to study the possible protective effect of growth hormone on cyclophosphamide-induced changes in the rat thymus gland. Sixty-four adult male albino rats were used and divided into three main groups. Group I (Control group). Group II (CP group) received 200 mg/kg body weight CP by a single intra-peritoneal injection. Group III (CP& GH group) received GH in a dose of 2 mg/kg body weight/day by subcutaneous injection starting 5 days before cyclophosphamide injection till the end of the experiment. Administration of CP (Group II) resulted in marked histopathological changes in thymus. Thymic cortex showed depletion of thymoblasts. There was a decrease in CD34 immune positively stained stem cells and an increase in CD68 immune positively stained macrophages. Ultrastructurally, thymoblasts were markedly degenerated and the most of epithelial reticular cells were vacuolated. Administration of GH (group III) showed preservation of the histological structure of the thymus. In conclusion, growth hormone could protect against cyclophosphamide induced thymic damage.

Lactiplantibacillus plantarum DLPT4 Protects Against Cyclophosphamide-Induced Immunosuppression in Mice by Regulating Immune Response and Intestinal Flora.

In this study, the strain Lactiplantibacillus plantarum DLPT4 was investigated for the immunostimulatory activity in cyclophosphamide (CTX)-induced immunosuppressed BALB/c mice. L. plantarum DLPT4 was administered to BALB/c mice by oral gavage for 30days, and CTX was injected intraperitoneally from the 25th to the 27th days. Intraperitoneal injection of CTX caused damage to the thymic cortex and intestines, and the immune dysfunction of the BALB/c mice. L. plantarum DLPT4 oral administration exerted immunoregulating effects evidenced by increasing serum immunoglobulin (IgA, IgG, and IgM) levels and reducing the genes expression of pro-inflammatory factors (IL-6, IL-1β, and TNF-α) of the CTX-induced immunosuppressed mice. The results of the metagenome-sequencing analysis showed that oral administration of L. plantarum DLPT4 could regulate the intestinal microbial community of the immunosuppressed mice by changing the ratio of Lactiplantibacillus and Bifidobacterium. Meanwhile, the abundance of carbohydrate enzyme (CAZyme), immune diseases metabolic pathways, and AP-1/MAPK signaling pathways were enriched in the mice administrated with L. plantarum DLPT4. In conclusion, oral administration of L. plantarum DLPT4 ameliorated symptoms of CTX-induced immunosuppressed mice by regulating gut microbiota, influencing the abundance of carbohydrate esterase in the intestinal flora, and enhancing immune metabolic activity. L. plantarum DLPT4 could be a potential probiotic to regulate the immune response.

The immunomodulatory activity of the betulonic acid based compound.

The immunomodulatory activity of a betulonic acid-based compound with furocoumarin (BABCF; 2-azido, 9-N-methylpiperazinomethyl oreozelone) has been investigated. Male C57BL/6 mice (aged 3 months) treated with the cytostatic agent cyclophosphamide (CP) and intact individuals served as experimental models. The expression of genes was studied in bone marrow (IL-12, IL-10, IL-1β, TNF-α, TGF-β, M-CSF, GM-CSF) or in the suspension of peritoneal cells (IL-12, IL-10; as the injection site). The surface markers of T-lymphocytes (CD3, CD4, and CD8) in fractions of venous blood mononuclear cells (MNCs) were determined by means of flow cytometry using antibodies. Histological and morphometric studies were performed to assess the impact of CP and BABCF on the thymus. BABCF caused a pronounced (about 3-fold) increase in relative expression of the GM-KSF gene. BABCF caused a local increase in the expression of IL-12 in the peritoneal cavity cells and restored the relative content of T-lymphocytes in the blood of CP-treated mice treated affecting mainly CD3⁺CD4⁺ lymphocytes. This substance reduced the tissue density of the thymic cortex and thymic medulla in CP-treated mice. Thus, results of this study suggest that BABCF exhibits a stimulating effect on the cellular link of immunity and promotes maintenance of the number of T-lymphocytes in the blood due to their migration from the central organs of the immune system.

Diversity in Cortical Thymic Epithelial Cells Occurs through Loss of a Foxn1-Dependent Gene Signature Driven by Stage-Specific Thymocyte Cross-Talk.

In the thymus, cortical thymic epithelial cells (cTECs) and medullary thymic epithelial cells support αβT cell development from lymphoid progenitors. For cTECs, expression of a specialized gene signature that includes Cxcl12, Dll4, and Psmb11 enables the cortex to support T lineage commitment and the generation and selection of CD4+CD8+ thymocytes. Although the importance of cTECs in T cell development is well defined, mechanisms that shape the cTEC compartment and regulate its functional specialization are unclear. Using a Cxcl12DsRed reporter mouse model, we show that changes in Cxcl12 expression reveal a developmentally regulated program of cTEC heterogeneity. Although cTECs are uniformly Cxcl12DsRed+ during neonatal stages, progression through postnatal life triggers the appearance of Cxcl12DsRed- cTECs that continue to reside in the cortex alongside their Cxcl12DsRed+ counterparts. This appearance of Cxcl12DsRed- cTECs is controlled by maturation of CD4-CD8-, but not CD4+CD8+, thymocytes, demonstrating that stage-specific thymocyte cross-talk controls cTEC heterogeneity. Importantly, although fate-mapping experiments show both Cxcl12DsRed+ and Cxcl12DsRed- cTECs share a common Foxn1+ cell origin, RNA sequencing analysis shows Cxcl12DsRed- cTECs no longer express Foxn1, which results in loss of the FOXN1-dependent cTEC gene signature and may explain the reduced capacity of Cxcl12DsRed- cTECs for thymocyte interactions. In summary, our study shows that shaping of the cTEC compartment during the life course occurs via stage-specific thymocyte cross-talk, which drives loss of Foxn1 expression and its key target genes, which may then determine the functional competence of the thymic cortex.

Effect of Serratula marginata dry extract on the mice thymus and spleen structure in cyclophosphamide immunosuppression

BACKGROUND: The search of effective and safe drugs to prevent and treating the immune deficient states is an actual problem of modern medicine.
 AIM: The purpose of the study is to evaluate the effect of Serratula marginata dry extract on structure of mice thymus and spleen at cyclophosphamide immunosuppression.
 MATERIALS AND METHODS: The experiments were carried out on F1 (CBAxC57Bl/6) mice. Immune deficiency was simulated by a single intraperitoneal introduction of cyclophosphamide in the dose 250 mg/kg. S. marginata dry extract in the dose 100 mg/kg was administered to animals for 14 days intragastrically against cyclophosphamide. Morphological studies of the thymus and spleen were performed on day 16 after the extracts administration. Areas white and red pulp of the spleen; the area of the thymic lobule, the cortex and the medulla; the density of cells in the subcapsular zone and the deep layers of the cortex were measured using the Zen 2012 image analysis program.
 RESULTS: The S. marginata extract limited the development of involutive changes in the thymus caused by cyclophosphamide: the thymus area was by 28% (p 0.05) higher and the cortical-medullary index was (ratio of the cortex area to the medulla area) by 26% higher. The number of mitotically dividing cells, blasts and large lymphocytes increased, the number of cells with structural disorders and macrophages decreased in the thymus cortex. In animals of the experimental groups, the white pulp area was 47% (p 0.05) higher than that in the control.
 CONCLUSIONS: The S. marginata dry extract limited the development of involutive processes in the thymus and spleen caused by the introduction of cytostatic cyclophosphamide.

Covalent TCR-peptide-MHC interactions induce T cell activation and redirect T cell fate in the thymus

Interactions between a T cell receptor (TCR) and a peptide-major histocompatibility complex (pMHC) ligand are typically mediated by noncovalent bonds. By studying T cells expressing natural or engineered TCRs, here we describe covalent TCR-pMHC interactions that involve a cysteine-cysteine disulfide bond between the TCR and the peptide. By introducing cysteines into a known TCR-pMHC combination, we demonstrate that disulfide bond formation does not require structural rearrangement of the TCR or the peptide. We further show these disulfide bonds still form even when the initial affinity of the TCR-pMHC interaction is low. Accordingly, TCR-peptide disulfide bonds facilitate T cell activation by pMHC ligands with a wide spectrum of affinities for the TCR. Physiologically, this mechanism induces strong Zap70-dependent TCR signaling, which triggers T cell deletion or agonist selection in the thymus cortex. Covalent TCR-pMHC interactions may thus underlie a physiological T cell activation mechanism that has applications in basic immunology and potentially in immunotherapy.

Immunohistochemical analysis of the thymus in newborn and adult yaks (Bos grunniens).

The thymus is the site of development and maturation of functional T lymphocytes and is critically important to the immune system. The purpose of this study was to examine the expression of markers of T lymphocytes, macrophages, dendritic cells, B lymphocytes and plasmocytes in the yak thymus. Twenty healthy male yaks were divided into newborn (2-4 weeks old, n = 10) and adult (3-4 years old, n = 10) group. qRT-PCR was used to evaluate the mRNA expression level of the main markers of the studied cell types. Immunohistochemistry was used to detect the distribution of CD3+ T lymphocytes, CD68+ macrophages, SIRPα+ dendritic cells, CD79α+ B lymphocytes, IgA and IgG+ plasmocytes. Within the same age group, the mRNA expression of CD3ε was highest (P < 0.05), followed by that of CD68, SIRPα, CD79α, IgG and IgA. Furthermore, CD3ε, CD68, and SIRPα mRNA expression levels were higher in newborn yaks than in the adult ones (P < 0.05), whereas those of CD79α, IgA, and IgG were higher in adults (P < 0.05). Immunohistochemical results showed localization of CD3+ T lymphocytes in the thymic cortex and medulla. CD68+ macrophages, SIRPα+ dendritic cells, CD79α+ B lymphocytes, IgA+ and IgG+ plasmocytes were mainly observed in the cortico-medullary region and medulla. In the same age group, the frequency of CD3+ T lymphocytes was higher than that of CD68+ macrophages and SIRPα+ dendritic cells (P < 0.05), followed by those of CD79α+ B lymphocytes and IgA+ and IgG+ plasmocytes. No significant difference was observed between B lymphocyte and plasmocyte frequencies in the yak thymus in both age groups (P > 0.05). The frequency of CD3+, CD68+ and SIRPα+ cells decreased from newborns to adults (P < 0.05). However, the frequencies of CD79α+, IgA+ and IgG+ cells increased from newborn to adult yaks (P < 0.05). The thymus of newborn yaks is well-developed, with higher numbers of T lymphocytes, macrophages, and dendritic cells than those in the adult thymus. However, higher frequencies of plasmocytes and B lymphocytes were detected in the adult thymus, suggesting that adults may better resist infections through humoral immunity as this organ undergoes involution. Furthermore, there was no significant difference in the number of IgA and IgG plasmocytes, which differs from what is observed in rodents and humans. This difference might be related to the fact that yaks live in low-oxygen plateaus.

STRUCTURAL MECHANISMS OF DISTURBANCES IN POSTNATAL MORPHOGENESIS OF THE IMMUNE SYSTEM ORGANS OF THE OFFSPRING BORN UNDER CONDITIONS OF THYROID HYPOFUNCTION IN THE MOTHER

The purpose of this study was to identify the structural and functional features of the postnatal development of the organs of the immune system of the offspring obtained under conditions of experimental hypothyroidism of pregnant women in the mother. The experiments were carried out on rat pups obtained from healthy females and obtained from females with experimental hypothyroidism. Studies have shown that maternal hypothyroidism leads to a disruption in the process of postnatal growth and formation of the immune system organs in offspring, the morphological manifestation of which is a decrease in the areas of the thymus cortex and T-dependent zones of the lymph nodes and spleen compared to the control, a decrease in proliferative activity and an increase in apoptosis T -lymphocytes both in the thymus and in T-dependent zones of peripheral immune organs. The mechanism of disturbances in the postnatal development of immune organs is based on an imbalance between the processes of apoptosis and proliferation of lymphoid cells, caused by a deficiency of thyroid hormones in the mother.

Effect ofBacillus subtilis onthe microarchitectural development ofthe immune system inSalmonella-challenged broiler chickens.

The effect ofBacillus subtilis onthe immune responses and morphometry ofthe immune organs was evaluated inbroilers challenged with S.gallinarum. For this purpose, Salmonella-free birds (n=240) were split into four groups with six replicates often birds each. Groups included anNC (negative control, non-infected+non-medicated), aPC-S (positive control, Salmonella-infected+non-medicated), anAT-S (Salmonella-infected+medicated with enrofloxacin), and aBS-S (Salmonella-infected+B.subtilis (2.0× 1010cfu/g; 0.1g/kg) group. Onday21, thethickness ofthe thymus cortex and medulla, germinal centre area ofthe spleen, bursal follicular length and bursal follicular area increased (P<0.05) inthe BS-S when compared tothe NC and PC-S groups. Onday35, theBS-S group exhibited ahigher (P<0.05) antibody titre against the Newcastle disease virus (NDV), and cortex ofthe thymus was thicker (P<0.05) compared tothe other groups. Adecrease inthe thymus medulla thickness, germinal area ofthe spleen and bursal follicular number were noted inthe PC-S group when compared totheother treatment groups. Inconclusion, the prophylactic use ofB.subtilis type probiotics alleviated the stress resulting from aSalmonella gallinarum infection and improved the immune organs development and function ininfected broilers.