Splenic White Pulp Research Articles

Blockade of the C5a–C5aR axis alleviates lung damage in hDPP4-transgenic mice infected with MERS-CoV

The pathogenesis of highly pathogenic Middle East respiratory syndrome coronavirus (MERS-CoV) remains poorly understood. In a previous study, we established an hDPP4-transgenic (hDPP4-Tg) mouse model in which MERS-CoV infection causes severe acute respiratory failure and high mortality accompanied by an elevated secretion of cytokines and chemokines. Since excessive complement activation is an important factor that contributes to acute lung injury after viral infection, in this study, we investigated the role of complement in MERS-CoV-induced lung damage. Our study showed that complement was excessively activated in MERS-CoV-infected hDPP4-Tg mice through observations of increased concentrations of the C5a and C5b-9 complement activation products in sera and lung tissues, respectively. Interestingly, blocking C5a production by targeting its receptor, C5aR, alleviated lung and spleen tissue damage and reduced inflammatory responses. More importantly, anti-C5aR antibody treatment led to decreased viral replication in lung tissues. Furthermore, compared with the sham treatment control, apoptosis of splenic cells was less pronounced in the splenic white pulp of treated mice, and greater number of proliferating splenic cells, particularly in the red pulp, was observed. These data indicate that (1) dysregulated host immune responses contribute to the severe outcome of MERS; (2) excessive complement activation, triggered by MERS-CoV infection, promote such dysregulation; and (3) blockade of the C5a–C5aR axis lead to the decreased tissue damage induced by MERS-CoV infection, as manifested by reduced apoptosis and T cell regeneration in the spleen. Therefore, the results of this study suggest a new strategy for clinical intervention and adjunctive treatment in MERS-CoV cases.

In vivo toxicity of the ribosome-inactivating lectin ebulin f in elderly mice.

Ebulin f is a ribosome-inactivating protein (RIP) present in green fruits of the dwarf elder (Sambucus ebulus L). Since dwarf elder fruits are used for food and as a medicine, we assessed the study of toxicological effects and safety of ebulin f in elderly mice, comparing these results with those reported in young animals and with other RIPs. Female Swiss mice aged 6 and 12 months of age were intraperitoneally injected with a single dose from 1.4 to 4.5 mg/kg ebulin f. Heart, stomach, intestines, lung, kidney, liver, spleen, pancreas, adrenal gland, uterus, ovary and brain were studied. Histology analysis was carried out by staining with hematoxylin and eosin and Masson's trichrome observed with a light microscope, or apoptosis detection by TUNEL method observed with a confocal laser microscope. Treated animals injected with the lower dose could recover their weights, but after 14 days half of them died. The higher dose caused a progressive loss of body weight leading to death. In the animals of the experimental groups it was found atrophy of Lieberkühn's crypts, pneumonia, nephronal degeneration, myocardial atrophy, centrolobular hepatic necrosis, splenic white pulp necrosis foci and increased rate of apoptosis in the intestines and liver, in which apoptoses were mainly located in the vicinity of the lobular central vein. We conclude that ebulin f affects vital organs in elderly mice.

Morphophysiological changes in the splenic extracellular matrix of Leishmania infantum-naturally infected dogs is associated with alterations in lymphoid niches and the CD4+ T cell frequency in spleens.

The spleen is one of the main affected organs in canine visceral leishmaniasis (CVL). Disorganization of the splenic white pulp (SWP) has been associated with immunosuppression and disease progression. This study aims to assess structural and cellular changes in the splenic extracellular matrix of dogs with CVL, correlating these changes with the parasite load and clinical signs. Splenic fragments were collected from 41 naturally infected animals for parasite load quantification by quantitative PCR, histopathological analysis and immunohistochemistry for CD3+, CD4+, and CD8+ T cells; CD21+ B cells; Ki-67+, IFN-γ+, and IL-10+ cells; and the MMP-9 and ADAM-10 enzymes. Laminin, collagen and fibronectin deposition were also evaluated. The animals were grouped according to the level of SWP organization. SWP disorganization was accompanied by a reduction in the quantity of lymphoid follicles/mm2 (p > 0.0001). Animals with moderate to intense SWP disorganization showed more clinical signs (p = 0.021), higher laminin (p = 0.045) and collagen deposition (p = 0.036), higher MMP-9 expression (p = 0.035) and lower numbers of CD4+ T cells (p = 0.027) in the spleen than the animals with organized SWP. These data suggest that splenic structure and function are drastically altered and compromised during CVL.

Neural architecture in lymphoid organs: Hard-wired antigen presenting cells and neurite networks in antigen entrance areas.

IntroductionRecently, we found abundant innervation of antigen presenting cells that were reached and enclosed by single neurites. These neurally hard‐wired antigen presenting cells (wAPC) could be observed in the T‐cell zone of superficial cervical lymph nodes of rats and other mammalians, including humans.MethodsAs a consequence, we investigated lymph nodes at many different anatomical positions as well as all primary and secondary lymphoid organs (SLO) in rodents for a similar morphology of innervation regarding antigen presenting cells known in those tissues.ResultsAs a result, we confirmed wAPC in lymph nodes independent from their draining areas and anatomical positions but also in all other T‐cell zones of lymphoid organs, like Peyer's patches, NALT and BALT, as well as in the thymic medulla. Other cells were innervated in a similar fashion but with seemingly missing antigen presenting capacity. Both types of innervated immune cells were observed as being also present in the dermis of the skin. Only in the spleen wAPC could not be detected. Beyond this systematic finding, we also found another regular phenomenon: a dense network of neurites that stained for neurofilament always in antigen entrance areas of lymphoid organs (subsinoidal layer of lymph nodes, subepithelial dome of Peyer's patches, subsinoidal layer of the splenic white pulp, margins of NALT and BALT). Lastly, also thymic epithelial cells (TEC) restricted to the corticomedullary junction of the thymus showed similar neurofilament staining.ConclusionsTherefore, we propose much more hard‐wired and probably afferent connections between lymphoid organs and the central nervous system than is hitherto known.

Bacterial and Pneumocystis Infections in the Lungs of Gene-Knockout Rabbits with Severe Combined Immunodeficiency.

Using the CRISPR/Cas9 gene-editing technology, we recently produced a number of rabbits with mutations in immune function genes, including FOXN1, PRKDC, RAG1, RAG2, and IL2RG. Seven founder knockout rabbits (F0) and three male IL2RG null (−/y) F1 animals demonstrated severe combined immunodeficiency (SCID), characterized by absence or pronounced hypoplasia of the thymus and splenic white pulp, and absence of immature and mature T and B-lymphocytes in peripheral blood. Complete blood count analysis showed severe leukopenia and lymphocytopenia accompanied by severe neutrophilia. Without prophylactic antibiotics, the SCID rabbits universally succumbed to lung infections following weaning. Pathology examination revealed severe heterophilic bronchopneumonia caused by Bordetella bronchiseptica in several animals, but a consistent feature of lung lesions in all animals was a severe interstitial pneumonia caused by Pneumocystis oryctolagi, as confirmed by histological examination and PCR analysis of Pneumocystis genes. The results of this study suggest that these SCID rabbits could serve as a useful model for human SCID to investigate the disease pathogenesis and the development of gene and drug therapies.

Prolonged follicular helper T cell responses in ME7 scrapie-infected mice

ABSTRACTWe previously reported that mice intracerebrally inoculated with the mouse-adapted scrapie strain ME7 have markedly diminished T zones in the spleen due to the decreased expression of CCL19 and CCL21. In addition, follicular dendritic cell networks in germinal centers were larger in ME7-infected spleens compared to uninfected spleens. As an extension of that study, we set out to determine how ME7 infection affects spleen structure and follicular helper T (Tfh) cell responses in mice. For this study, mice were intraperitoneally inoculated with brain homogenate of the ME7 inoculum and spleens were analyzed 50, 130, and 200 days after inoculation and compared with those from uninfected mice. The result showed that ME7- infected mice had increased Tfh cell responses which were maintained until end-stage prion disease. Although CD4 T cells decreased in white pulps, they increased in germinal centers, and expressed higher levels of the Tfh-related genes, such as Bcl6, Il21, Cxcr5, Icos, and Pdcd1. In addition, ME7-infected spleens had increased numbers of CD4 memory T cells. These data indicate that although ME7 infection led to impaired splenic white pulp structure, CD4 memory T cells were increased and Tfh cell responses were required and prolonged to provide help for the replication and accumulation of pathogenic prion protein in germinal centers.

Capillary networks and follicular marginal zones in human spleens. Three-dimensional models based on immunostained serial sections.

We have reconstructed small parts of capillary networks in the human splenic white pulp using serial sections immunostained for CD34 alone or for CD34 and CD271. The three-dimensional (3D) models show three types of interconnected networks: a network with very few long capillaries inside the white pulp originating from central arteries, a denser network surrounding follicles plus periarterial T-cell regions and a network in the red pulp. Capillaries of the perifollicular network and the red pulp network have open ends. Perifollicular capillaries form an arrangement similar to a basketball net located in the outer marginal zone. The marginal zone is defined by MAdCAM-1+ marginal reticular stromal cells. Perifollicular capillaries are connected to red pulp capillaries surrounded by CD271+ stromal capillary sheath cells. The scarcity of capillaries inside the splenic white pulp is astonishing, as non-polarised germinal centres with proliferating B-cells occur in adult human spleens. We suggest that specialized stromal marginal reticular cells form a barrier inside the splenic marginal zone, which together with the scarcity of capillaries guarantees the maintenance of gradients necessary for positioning of migratory B- and T-lymphocytes in the human splenic white pulp.

Spirulina ameliorates methotrexate hepatotoxicity via antioxidant, immune stimulation, and proinflammatory cytokines and apoptotic proteins modulation

AimsMethotrexate (MTX) is an efficient cytotoxic drug used against various carcinogenic, inflammatory and autoimmune diseases; however, the hepatotoxicity of MTX limits its use. Therefore, the present study aimed to evaluate the potential hepatoprotective and immune-stimulant effect of Spirulina platensis (SP) against MTX acute toxicity. Main methodsThirty-two male Wistar rats were randomly allocated into the following four groups (n = 8): control, SP (500 mg/kg bwt, oral gavage daily for 21 days), MTX (20 mg/kg bwt, single ip injection), and MTX+SP. Hepatic and splenic histoarchitecture, leukocyte counts and serum immunoglobulins were evaluated. Hepatic oxidant/antioxidant status, proinflammatory cytokines (tumor necrosis factor-α, and interleukin 6), and pro-apoptotic proteins (caspase 3 and Bax) immunoexpression were assessed. Key findingsMTX induced extensive hepatic necrosis and vacuolation, and sever lymphoid depletion in splenic white pulp with increased levels of serum transaminases, lactate dehydrogenase, and hepatic malondialdehyde, tumor necrosis factor-α and interleukin 6; and number of caspase 3- and Bax-positive hepatocytes. A significant decrease in leukocyte counts, serum immunoglobulins (IgA, IgM and IgG) level, and hepatic antioxidant enzymes (GSH, GPx, SOD, and CAT) was also detected. Pretreatment with SP resulted in significant improvements in hepatic and splenic histologic architecture, as well as restoring liver enzymes and reduction of lipid peroxidation product, proinflammatory cytokines, and caspase 3 and Bax immunoexpression. Additionally, a significant increase in antioxidant enzymes, serum immunoglobulins, and total leukocyte counts was demonstrated. SignificanceSP possesses promising antioxidant, anti-inflammatory, anti-apoptotic and immune stimulatory properties against MTX-induced hepatotoxicity and immunosuppression.

Origin and Differentiation Trajectories of Fibroblastic Reticular Cells in the Splenic White Pulp

The splenic white pulp is underpinned by poorly characterized stromal cells that demarcate distinct immune cell microenvironments. Here, definition of the embryonic origin and tracing of the differentiation trajectories of fibroblastic reticular cells (FRCs) was enabled by the establishment of FRC-specific fate-mapping in mice. We found that all reticular cell subsets descend from pluripotent progenitors that emerge at embryonic day 19.5 from Sca-1 periarterial progenitors. Commitment of FRC progenitors was concluded during the first week of postnatal life through occupation of niches along developing central arterioles. Single cell transcriptomic analysis facilitated deconvolution of FRC differentiation trajectories and indicated that perivascular reticular cells function both as adult lymphoid organizer cells and mural cell progenitors. Finally, the lymphotoxin-β receptor-independent sustenance of postnatal progenitor stemness unveiled that systemic immune surveillance in the splenic white pulp is governed through subset specification of reticular cells from a pluripotent periarterial progenitor cell.

Immunomodulatory Effects of Kuseonwangdogo-Based Mixed Herbal Formula Extracts on a Cyclophosphamide-Induced Immunosuppression Mouse Model.

Aim Kuseonwangdogo is a traditional Korean immunomodulatory polyherbal prescription. However, there are no systemic findings on its complex immunomodulatory effects on in vivo models. In this study, we observed the immunomodulatory effects of Kuseonwangdogo-based mixed herbal formula aqueous extracts (MHFe) on cyclophosphamide- (CPA-) induced immunosuppression mouse model. Methods In total, 60 male 6-week-old ICR mice (10 mice/group) were selected based on body weight 24 h after the second CPA treatment and used in this experiment. Twelve hours after the end of the last (fourth) oral administration of MHFe, the animals were sacrificed. Results Following CPA treatment, a noticeable decrease in the body, thymus, spleen, and submandibular lymph node (LN) weights; white blood cell, red blood cell, platelet number, hemoglobin, and hematocrit concentrations; serum interferon-γ levels; splenic tumor necrosis factor-α, interleukin- (IL-) 1β, and IL-10 content; and peritoneal and splenic natural killer cell activities was observed. Depletion of lymphoid cells in the thymic cortex, splenic white pulp, and submandibular LN-related atrophic changes were also observed. However, these CPA-induced myelosuppressive signs were markedly and dose-dependently inhibited by the oral administration of 125, 250, and 500 mg/kg MHFe. Conclusion MHFe can be a promising, potent immunomodulatory therapeutic agent for various immune disorders.

Effects of intragastrically-administered Tepary bean lectins on digestive and immune organs: Preclinical evaluation.

Previous work showed that Tepary bean (Phaseolus acutifolius) lectins exhibit differential cytotoxic effects on cancer cell lines by apoptosis induction. In vivo studies using a Tepary bean lectin fraction (TBLF, 50 mg/kg of body weight) after colon cancer induction in rats showed that TBLF inhibited early precancerous lesions without systemic toxicity however, loss of body weight gain and activation of immune cells were observed. In order to know more about the possible adverse effects, we evaluated the administration of TBLF on digestive and immune organs. Sprague Dawley rats were administered TBLF for six weeks and allowed to recover for two weeks. Immune activation was observed through an increased lymphocyte-granulocyte ratio, an increased number of lymphoid follicles in intestinal Peyer's patches and a slight expansion of the splenic white pulp. Atrophy was observed in small intestine villi and crypt foci of the colon without normalization after the recovery period. Pancreas histopathology showed hypertrophy after the six-week administration period, particularly vacuolation and trabecular widening; but after the two-week recovery period atrophy was observed, suggesting a partial compensatory type process. Our results show that TBLF activates the immune system and affects digestive organs through direct interaction with intestinal epithelium, and indirectly by producing pancreatic hyperfunction. Further work will focus in longer recuperation periods after TBLF treatment.

Perivascular Fibroblasts of the Developing Spleen Act as LTα1β2-Dependent Precursors of Both T and B Zone Organizer Cells

T and B cell compartmentalization is a hallmark of secondary lymphoid organs and is maintained by chemokine-expressing stromal cells. How this stromal cell network initially develops and differentiates into two distinct subsets is poorly known, especially for the splenic white pulp (WP). Here, we show that perivascular fibroblast precursors are triggered by LTα1β2 signals to expand, express CCL19/21, and then differentiate into two functionally distinct fibroblast subsets responsible for B and Tcell clustering and WP compartmentalization. Failure to express or sense CCL19 leads to impaired T zone development, while lack of B cells or LTα1β2 leads to an earlier and stronger impairment in WP development. We therefore propose that WP development proceeds in multiple steps, with LTα1β2+ B cells acting as major inducer cells driving the expansion and gradual differentiation of perivascular fibroblasts into T and B zone organizer cells.

Experimental sporotrichosis in a cyclophosphamide-induced immunosuppressed mice model.

This report describes a model of host resistance for Sporothrix schenckii, an opportunistic fungi in immunosuppressed mice with cyclophosphamide (CY) to be used in studies of immunotoxicology and immunopharmacology. Two doses of CY were administered intraperitoneally: 200mg/kg and a booster of 150mg/kg at 9-day intervals. Three days after the first dose of CY the animals were infected subcutaneously with 1.8 × 108 yeast/ml (S. schenckii ATCC 16345). At 7 and 14 days post-infection, the animals were euthanized and analyzed the fungal load by unit forming colony count in the spleen and popliteal lymph nodes. The relative weight of thymus and spleen, splenic index, the frequency of T and B cells in spleen by flow cytometry, the hind paw inflammation index and cytokine (interleukin [IL]-17, IL-10, and interferon [IFN]-γ) profile were measured. Histopathological studies of the spleen and the hind paw were also assessed. The immunosuppression status was confirmed at the evaluated days by reduction of relative weight of thymus, reduction of the splenic white pulp, the population of B and T lymphocytes, and the cytokine profile in the treated mice with CY in comparison with nontreated groups, associated to higher fungal load in hind paw and spleen in the infected mice. The described model reveals an increasing in susceptibility to infection and severity when associated with immunosuppression. This model can serve as a reference for studies of S. schenckii host resistance in pharmaceutical and toxicological studies.

The Small Rho GTPases Rac1 and Rac2 Are Important for T-Cell Independent Antigen Responses and for Suppressing Switching to IgG2b in Mice.

The Rho GTPases Cdc42, Rac1, and Rac2 coordinate receptor signaling to cell adhesion, migration, and proliferation. Deletion of Rac1 and Rac2 early during B cell development leads to failure in B cell entry into the splenic white pulp. Here, we sought to understand the role of Rac1 and Rac2 in B cell functionality and during the humoral antibody response. To circumvent the migratory deficiency of B cells lacking both Rac1 and Rac2, we took the approach to inducibly delete Rac1 in Rac2−/− B cells in the spleen (Rac1BRac2−/− B cells). Rac1BRac2−/− mice had normal differentiation of splenic B cell populations, except for a reduction in marginal zone B cells. Rac1BRac2−/− B cells showed normal spreading response on antibody-coated layers, while both Rac2−/− and Rac1BRac2−/− B cells had reduced homotypic adhesion and decreased proliferative response when compared to wild-type B cells. Upon challenge with the T-cell-independent antigen TNP-conjugated lipopolysaccharide, Rac1BRac2−/− mice showed reduced antibody response. In contrast, in response to the T-cell-dependent antigen sheep red blood cells, Rac1BRac2−/− mice had increased serum titers of IgG1 and IgG2b. During in vitro Ig class switching, Rac1BRac2−/− B cells had elevated germline γ2b transcripts leading to increased Ig class switching to IgG2b. Our data suggest that Rac1 and Rac2 serve an important role in regulation of the B cell humoral immune response and in suppressing Ig class switching to IgG2b.

In Vivo Radioprotective Activity of Cell-Permeable Bifunctional Antioxidant Enzyme GST-TAT-SOD against Whole-Body Ionizing Irradiation in Mice.

GST-TAT-SOD was the fusion of superoxide dismutase (SOD), cell-permeable peptide TAT, and glutathione-S-transferase (GST). It was proved to be a potential selective radioprotector in vitro in our previous work. This study evaluated the in vivo radioprotective activity of GST-TAT-SOD against whole-body irradiation. We demonstrated that intraperitoneal injection of 0.5 ml GST-TAT-SOD (2 kU/ml) 2 h before the 6 Gy whole-body irradiation in mice almost completely prevented the splenic damage. It could significantly enhance the splenic antioxidant activity which kept the number of splenic white pulp and consequently resisted the shrinkage of the spleen. Moreover, the thymus index, hepatic antioxidant activity, and white blood cell (WBC) count of peripheral blood in irradiated mice pretreated with GST-TAT-SOD also remarkably increased. Although the treated and untreated irradiated mice showed no significant difference in the growth rate of animal body weight at 7 days postirradiation, the highest growth rate of body weight was observed in the GST-TAT-SOD-pretreated group. Furthermore, GST-TAT-SOD pretreatment increased resistance against 8 Gy whole-body irradiation and enhanced 30 d survival. The overall effect of GST-TAT-SOD seemed to be a bit more powerful than that of amifostine. In conclusion, GST-TAT-SOD would be a safe and potentially promising radioprotector.

Histological characteristics of rats` spleen in conditions of general dehydration.

Background. The study of morphological changes of immune organs in conditions of extreme factors still remains one of the most important in medicine due to daily influence of negative factors on the body. Dehydration is a stressful agent, often influencing human body in natural conditions and in the conditions of specific manufacture. Objective. To compare the changes of structural spleen components in conditions of experimental dehydration of rats of light and moderate degrees. Methods. The object of the study were 18 outbred white adult rats. 6 animals formed the control group. The group of experimental rats was in conditions of general dehydration by A.D.Soboleva: they were on a completely anhydrous diet. They were fed with granulated feed. In the first group (6 rats) we simulated mild dehydration, which was reached within three days. In the second group (6 rats) we simulated moderate degree of dehydration when water shortage was achieved within 6-7 days of the experiment. In order to study the structural components of the spleen histological sections were stained with hematoxylin-eosin, by the method of Van Gieson, and PAS-reaction was conducted. Results. Under the light microscopy rats` spleen of the control group has typical for rats structure. On the 3rd day of the experiment (mild dehydration) the conducted histological studies of the spleen showed, that medium-sized lymphoid follicles with well-distinguished T and B zones dominate in the white pulp. In some follicles the boundaries of reactive centers are expanded, there are strengthened macrophage and plasmocyte reactions. On the 6th day of the experiment (mild dehydration) medium follicles dominate in 2/3 of observations, more seldom - large. In large and medium-sized follicles we determine T- and B-zones. In 1/3 of observations we determine small follicles and almost no medium and large specimens. Small follicles are devastated, they are presented by T-lymphocytes, B-zones are not defined or expressed very poorly. There is increased plethora of the red pulp. The density of immune cells is moderate and focal accumulations of T -lymphocytes are not numerous. Conclusion. It was determined that within both terms of the experiment dehydration leads to similar morphological changes in the spleen. There is a slight hyperplasia of the white pulp in the spleen on the 3rd day of general dehydration. On the 6th day in the majority of the observations we determined signs of severe hyperplasia of the white pulp. At the same time, a small number of observations in the white pulp show small follicles, presented only by T-lymphocytes. This shows the signs of a gradual depletion of splenic white pulp with general dehydration of average degree.

Splenic Marginal Zone Lymphoma: A Case Report with Review of Literature Running Title: A Rare Case Report On Splenic Marginal Zone Lymphoma

Splenic marginal zone lymphoma(SMZL) is a rare B-cell neoplasm comprising less than 2% of lymphoid neoplasms ,composed of small lymphocytes which surround and replace the splenic white pulp ,germinal centres,follicle mantle and merge with marginal zone.We report a case of SMZL in a 40 year old male patient presenting with complaints of low grade fever and left sided abdominal discomfort for 6 months and was noted to have massive splenomegaly on physical examination. Laboratory evaluation revealed leucocytosis and presence of atypical lymphocytes which were larger than mature lymphocytes having moderately basophilic cytoplasm with cytoplasmic processes at the poles of the cell with round to oval nucleus with clumped chromatin and indistinct nucleoli.Immunophenotypic analysis revealed a B-cell population with CD -20 positivity.

Identification of secreted and membrane-bound bat immunoglobulin using a Microchiropteran-specific mouse monoclonal antibody

Bat immunity has received increasing attention because some bat species are being decimated by the fungal disease, White Nose Syndrome, while other species are potential reservoirs of zoonotic viruses. Identifying specific immune processes requires new specific tools and reagents. In this study, we describe a new mouse monoclonal antibody (mAb) reactive with Eptesicus fuscus immunoglobulins. The epitope recognized by mAb BT1-4F10 was localized to immunoglobulin light (lambda) chains; hence, the mAb recognized serum immunoglobulins and B lymphocytes. The BT1-4F10 epitope appeared to be restricted to Microchiropteran immunoglobulins and absent from Megachiropteran immunoglobulins. Analyses of sera and other E. fuscus fluids showed that most, if not all, secreted immunoglobulins utilized lambda light chains. Finally, mAb BT1-4F10 permitted the identification of B cell follicles in splenic white pulp. This Microchiropteran-specific mAb has potential utility in seroassays; hence, this reagent may have both basic and practical applications for studying immune process.

Bystander-activated memory T lymphocytes cluster around infected cells early after infection

Abstract Innate and adaptive immune responses are typically considered to occur sequentially following an infection. The innate immune system responds initially to an infection and the antigen-specific T and B cell response develops subsequently. Although the peak of the antigen-specific T cell response lags days behind the innate response, inflammatory signals lead to rapid expression of Granzyme B and Interferon-γ in memory CD8+ T cells. This occurs in a T cell receptor (TCR) independent manner and is referred to as “bystander activation.” We and others have demonstrated that these bystander-activated cytotoxic T lymphocytes (BA-CTL) can kill target cells in an NKG2D-dependent, TCR-independent fashion early after infection. This suggests that T cells use innate-like mechanisms for rapid TCR-independent responses to infection. Here we report that during WT Listeria monocytogenes (LM) infection, antigen non-specific BA-CTL rapidly migrate to cluster around infected cells, surrounding foci of LM in splenic white pulp at 24h post infection. These clusters at early time-points closely resemble antigen-specific effector T cell clustering on day 7 post-infection. We describe the mechanisms driving this early activation and define distinct stages of this innate-like effector program. We propose that the purpose of driving bystander-activated T cells to sites of infection and eliciting these innate-like functional capacities is to limit early pathogen replication.

Innate lymphoid cells in secondary lymphoid organs.

The family of innate lymphoid cells (ILCs) has attracted attention in recent years as its members are important regulators of immunity, while they can also cause pathology. In both mouse and man, ILCs were initially discovered in developing lymph nodes as lymphoid tissue inducer (LTi) cells. These cells form the prototypic members of the ILC family and play a central role in the formation of secondary lymphoid organs (SLOs). In the absence of LTi cells, lymph nodes (LN) and Peyer's Patches (PP) fail to form in mice, although the splenic white pulp can develop normally. Besides LTi cells, the ILC family encompasses helper-like ILCs with functional distinctions as seen by T-helper cells, as well as cytotoxic natural killer (NK) cells. ILCs are still present in adult SLOs where they have been shown to play a role in lymphoid tissue regeneration. Furthermore, ILCs were implicated to interact with adaptive lymphocytes and influence the adaptive immune response. Here, we review the recent literature on the role of ILCs in secondary lymphoid tissue from the formation of SLOs to mature SLOs in adults, during homeostasis and pathology.