Psoriasis is a common, chronic, inflammatory skin disorder. A number of genetic loci have been shown to confer risk for psoriasis. Collectively, these offer an integrated model for the inherited basis for susceptibility to psoriasis that combines altered skin barrier function together with the dysregulation of innate immune pathogen sensing and adaptive immunity. The major histocompatibility complex (MHC) harbours the psoriasis susceptibility region which exhibits the largest effect size, driven in part by variation contained on the HLA-Cw*0602 allele. However, the resolution of the number and genomic location of potential independent risk loci are hampered by extensive linkage disequilibrium across the region. We leveraged the power of large psoriasis case and control data sets and the statistical approach of conditional analysis to identify potential further association signals distributed across the MHC. In addition to the major loci at HLA-C (P = 2.20 × 10−236), we observed and replicated four additional independent signals for disease association, three of which are novel. We detected evidence for association at SNPs rs2507971 (P = 6.73 × 10−14), rs9260313 (P = 7.93 × 10−09), rs66609536 (P = 3.54 × 10−07) and rs380924 (P = 6.24 × 10−06), located within the class I region of the MHC, with each observation replicated in an independent sample (P ≤ 0.01). The previously identified locus is close to MICA, the other three lie near MICB, HLA-A and HCG9 (a non-coding RNA gene). The identification of disease associations with both MICA and MICB is particularly intriguing, since each encodes an MHC class I-related protein with potent immunological function.
γδ T cells, a lineage of innate-like lymphocytes, are distinguished from conventional αβ T cells in their antigen-recognition, cell activation requirements and effector functions. γδ T cells have been implicated in the pathology of several human autoimmune and inflammatory diseases and their corresponding mouse models, but their specific roles in these diseases have not been elucidated. We report that γδTCR+ cells including both the CD27−CD44hi and CD27+CD44lo subsets infiltrate islets of pre-diabetic non-obese diabetic (NOD) mice. Moreover, NOD CD27−CD44hi and CD27+CD44lo γδ T cells were pre-programmed to secrete IL-17, or IFN-γ upon activation. Adoptive transfer of T1D to T and B lymphocyte-deficient NOD recipients was greatly potentiated when γδ T cells, and specifically the CD27− γδ T cell subset, were included compared to transfer of αβ T cells alone. Antibody-mediated blockade of IL-17 prevented T1D transfer in this setting. Moreover, introgression of genetic Tcrd deficiency onto the NOD background provided robust T1D protection, supporting a non-redundant, pathogenic role of γδ T cells in this model. The potent contributions of CD27− γδ T cells and IL-17 to islet inflammation and diabetes reported here suggest that these mechanisms may also underlie human T1D.
Epithelial cells respond to physico-chemical damage with up-regulation of major histocompatbility complex–like ligands that can activate the cytolytic potential of neighboring intraepithelial T cells by binding the activating receptor, NKG2D. The systemic implications of this lymphoid stress-surveillance response, however, are unknown. We found that antigens encountered at the same time as cutaneous epithelial stress induced strong primary and secondary systemic, T helper 2 (TH2)–associated atopic responses in mice. These responses required NKG2D-dependent communication between dysregulated epithelial cells and tissue-associated lymphoid cells. These data are germane to uncertainty over the afferent induction of TH2 responses and provide a molecular framework for considering atopy as an important component of the response to tissue damage and carcinogenesis.
Polyaromatic hydrocarbons (PAHs) are prevalent, potent carcinogens, and 7,12-dimethylbenz[a]anthracene (DMBA) is a model PAH widely used to study tumorigenesis. Mice lacking Langerhans cells (LCs), a signatory epidermal dendritic cell (DC), are protected from cutaneous chemical carcinogenesis, independent of T cell immunity. Investigation of the underlying mechanism revealed that LC-deficient skin was relatively resistant to DMBA-induced DNA damage. LCs efficiently metabolized DMBA to DMBA-trans-3,4-diol, an intermediate proximal to oncogenic Hras mutation, and DMBA-treated LC-deficient skin contained significantly fewer Hras mutations. Moreover, DMBA-trans-3,4-diol application bypassed tumor resistance in LC-deficient mice. Additionally, the genotoxic impact of DMBA on human keratinocytes was significantly increased by prior incubation with human-derived LC. Thus, tissue-associated DC can enhance chemical carcinogenesis via PAH metabolism, highlighting the complex relation between immune cells and carcinogenesis.
Psoriasis is an immune-mediated skin disorder that is inherited as a complex genetic trait. Although genome-wide association scans (GWAS) have identified 36 disease susceptibility regions, more than 50% of the genetic variance can be attributed to a single Major Histocompatibility Complex (MHC) locus, known as PSORS1. Genetic studies indicate that HLA-C is the strongest PSORS1 candidate gene, since markers tagging HLA-Cw*0602 consistently generate the most significant association signals in GWAS. However, it is unclear whether HLA-Cw*0602 is itself the causal PSORS1 allele, especially as the role of SNPs that may affect its expression has not been investigated. Here, we have undertaken an in-depth molecular characterization of the PSORS1 interval, with a view to identifying regulatory variants that may contribute to disease susceptibility. By analysing high-density SNP data, we refined PSORS1 to a 179 kb region encompassing HLA-C and the neighbouring HCG27 pseudogene. We compared multiple MHC sequences spanning this refined locus and identified 144 candidate susceptibility variants, which are unique to chromosomes bearing HLA-Cw*0602. In parallel, we investigated the epigenetic profile of the critical PSORS1 interval and uncovered three enhancer elements likely to be active in T lymphocytes. Finally we showed that nine candidate susceptibility SNPs map within a HLA-C enhancer and that three of these variants co-localise with binding sites for immune-related transcription factors. These data indicate that SNPs affecting HLA-Cw*0602 expression are likely to contribute to psoriasis susceptibility and highlight the importance of integrating multiple experimental approaches in the investigation of complex genomic regions such as the MHC.
To gain further insight into the genetic architecture of psoriasis, we conducted a meta-analysis of three genome-wide association studies (GWAS) and two independent datasets genotyped on the Immunochip, involving 10,588 cases and 22,806 controls in total. We identified 15 new disease susceptibility regions, increasing the number of psoriasis-associated loci to 36 for Caucasians. Conditional analyses identified five independent signals within previously known loci. The newly identified shared disease regions encompassed a number of genes whose products regulate T-cell function (e.g. RUNX3, TAGAP and STAT3). The new psoriasis-specific regions were notable for candidate genes whose products are involved in innate host defense, encoding proteins with roles in interferon-mediated antiviral responses (DDX58), macrophage activation (ZC3H12C), and NF-κB signaling (CARD14 and CARM1). These results portend a better understanding of shared and distinctive genetic determinants of immune-mediated inflammatory disorders and emphasize the importance of the skin in innate and acquired host defense.
Psoriasis is an inflammatory skin disorder that is inherited as a complex trait. Genetic studies have repeatedly highlighted HLA-C as the major determinant for psoriasis susceptibility, with the Cw*0602 allele conferring significant disease risk in a wide-range of populations. Despite the potential importance of HLA-C variation in psoriasis, either via an effect on peptide presentation or immuno-inhibitory activity, allele-specific expression patterns have not been investigated. Here, we used reporter assays to characterize two regulatory variants, which virtually abolished the response to TNF-α (rs2524094) and IFN-γ (rs10657191) in HLA-Cw*0602 and a cluster of related alleles. We validated these findings through the analysis of HLA-Cw*0602 expression in primary keratinocytes treated with TNF-α and IFN-γ. Finally, we showed that HLA-Cw*0602 transcripts are not increased in psoriatic skin lesions, despite highly elevated TNF-α levels. Thus, our findings demonstrate the presence of allele-specific differences in HLA-C expression and indicate that HLA-Cw*0602 is unresponsive to up-regulation by key pro-inflammatory cytokines in psoriasis. These data pave the way for functional studies into the pathogenic role of the major psoriasis susceptibility allele.
The Regulator of G Protein Signaling 1 [RGS1] gene is associated with celiac disease, multiple sclerosis (MS) and Type I diabetes (T1D), which are all T cell-mediated pathologies. And yet there is no reported analysis of RGS1 biology in human T cells. This study shows that RGS1 expression is substantially higher in T cells from human gut versus peripheral blood, and that this can be exaggerated in intestinal inflammation. Elevated RGS1 levels profoundly reduce T cell migration to lymphoid-homing chemokines, whereas RGS-1 depletion selectively enhances such chemotaxis in gut T cells, and impairs their colitogenic potential. These findings provide a revised framework in which to view the linkage of RGS1 to inflammatory disease.
The Infectious Diseases BioBank (IDB) has consistently archived peripheral blood mononuclear cell (PBMNC) RNA for transcriptome analyses. RNA is particularly labile, and hence, these samples provide a sensitive indicator for assessing the IDB's quality-assurance measures. Independent analyses of 104 PBMNC RNA specimens from 26 volunteers revealed that the mean RNA integrity number (RIN) was high (9.02), although RIN ranged between scores of 7 and 10. This variation of RIN values was not associated with ischemic time, PBMNC quality, number of samples processed per day, self-medication after immunization, freezer location, donor characteristics, differential white blood cell counts, or daily variation in RNA extractions (all P>0.05). RIN values were related to the date of collection, with those processed during mid-summer having highest RIN scores (P=0.0001). Amongst specimens with the lowest RIN scores, no common feature could be identified. Thus, no technical explanation for the variation in RNA quality could be ascertained and these may represent normal physiological variations. These data provide strong evidence that current IDB protocols for the isolation and preservation PBMNC RNA are robust.
Infection or stimulation of the innate immune system by nonspecific microbial antigens is thought to educate the immune system to respond appropriately to allergens, preventing allergy.
To determine the immunologic pathways that might explain how infection/microbial exposure inhibits allergic sensitization.
Immunologic studies of non-antigen-specific functions of CD8 memory cells, their maturation in vivo, and their effects in a mouse asthma model, to test the hypothesis that CD8 memory is shaped by innate immunity in a way that can inhibit allergic disease.
We found that CD8 memory T-cell (CD8 Tm) populations bridge innate and adaptive immunity by responding to either antigen or cytokines alone. CD8 Tm populations partially subvert the clonal selection process by activating their neighbors through induction of dendritic cell IL-12. Stimulation of innate or acquired immunity in the lung or gut causes expansion/maturation of CD8 Tm populations, which provide an early source of cytokines, enhance TH1 immunity, and inhibit allergic sensitization and airway inflammation/hyperresponsiveness in a non-antigen-specific fashion.
CD8 T-cell–mediated immune memory is long-lived and can retain its capacity for rapid cytokine release in a nonantigen-specific fashion. This novel type of memory enhances TH1 over TH2 immunity and prevents allergic sensitization after exposure to environmental antigens or infection.
CD8 T cell; immunologic memory; innate immunity; allergy; TH1/TH2; dendritic cell; IL-12
The conjunctiva contains a specialized population of lymphocytes that reside in the epithelium, named intraepithelial lymphocytes (IEL).
Here we characterized the IEL population prior to and after experimental desiccating stress (DS) for 5 or 10 days (DS5, DS10) and evaluated the effect of NK depletion on DS. The frequency of IELs in normal murine conjunctiva was CD3+CD103+ (∼22%), CD3+γδ+ (∼9.6%), CD3+NK+ (2%), CD3−NK+ (∼4.4%), CD3+CD8α (∼0.9%), and CD4 (∼0.6%). Systemic depletion of NK cells prior and during DS led to a decrease in the frequency of total and activated DCs, a decrease in T helper-17+ cells in the cervical lymph nodes and generation of less pathogenic CD4+T cells. B6.nude recipient mice of adoptively transferred CD4+T cells isolated from NK-depleted DS5 donor mice showed significantly less corneal barrier disruption, lower levels of IL-17A, CCL20 and MMP-3 in the cornea epithelia compared to recipients of control CD4+T cells.
Taken together, these results show that the NK IELs are involved in the acute immune response to desiccation-induced dry eye by activating DC, which in turn coordinate generation of the pathogenic Th-17 response.
The thymic medulla provides a specialized microenvironment for the negative selection of T cells, with the presence of autoimmune regulator (Aire)-expressing medullary thymic epithelial cells (mTECs) during the embryonic-neonatal period being both necessary and sufficient to establish long-lasting tolerance. Here we showed that emergence of the first cohorts of Aire+ mTECs at this key developmental stage, prior to αβ T cell repertoire selection, was jointly directed by Rankl+ lymphoid tissue inducer cells and invariant Vγ5+ dendritic epidermal T cell (DETC) progenitors that are the first thymocytes to express the products of gene rearrangement. In turn, generation of Aire+ mTECs then fostered Skint-1-dependent, but Aire-independent, DETC progenitor maturation and the emergence of an invariant DETC repertoire. Hence, our data attributed a functional importance to the temporal development of Vγ5+ γδ T cells during thymus medulla formation for αβ T cell tolerance induction and demonstrated a Rank-mediated reciprocal link between DETC and Aire+ mTEC maturation.
► Invariant Vγ5+ thymocytes regulate formation of Aire+ medullary thymic epithelium ► Generation of an invariant Vγ5+ T cell population requires thymus medulla development ► Skint-1-mediated Vγ5+ thymocyte development is Aire independent ► Dependency on Tnfrsf11a links γδ T cell and medullary epithelium development
γδ T cells mediate rapid tissue responses in murine skin and participate in cutaneous immune regulation including protection against cancer. The role of human γδ cells in cutaneous homeostasis and pathology is poorly characterized.
In this study we show in vivo evidence that human blood contains a distinct subset of pro-inflammatory cutaneous lymphocyte antigen (CLA) and C-C chemokine receptor (CCR) 6 positive Vγ9Vδ2 T cells, which is rapidly recruited into perturbed human skin. Vγ9Vδ2 T cells produced an array of pro-inflammatory mediators including IL-17A and activated keratinocytes in a TNF-α and IFN-γ dependent manner.
Examination of the common inflammatory skin disease psoriasis revealed a striking reduction of circulating Vγ9Vδ2 T cells in psoriasis patients compared to healthy controls and atopic dermatitis patients. Decreased numbers of circulating Vγ9Vδ2 T cells normalized after successful treatment with psoriasis-targeted therapy. Together with the increased presence of Vγ9Vδ2 T cells in psoriatic skin, this data indicates redistribution of Vγ9Vδ2 T cells from the blood to the skin compartment in psoriasis.
In summary, we report a novel human pro-inflammatory γδ T cell involved in skin immune surveillance with immediate response characteristics and with potential clinical relevance in inflammatory skin disease.
Frequent microbial and non-microbial challenges to epithelial cells trigger discrete pathways, promoting molecular changes, such as the secretion of specific cytokines and chemokines, and alterations to molecules displayed at the epithelial cell surface. In combination, these molecules impose major decisions on innate and adaptive immune cells. Depending on context, those decisions can be as diverse as those imposed by professional antigen presenting cells, benefitting the host by balancing immune competence with the avoidance of immunopathology. Nonetheless, this potency of epithelial cells is also consistent with the causal contribution of epithelial dysregulation to myriad inflammatory diseases. This pathogenic axis provides an attractive target for tissue-specific clinical manipulation. In this context, a research goal should be to identify all molecules used by epithelial cells to instruct immune cells. We term this the epimmunome.
T-pro are tumor-infiltrating TCRαβ+CD8+ cells of reduced cytotoxic potential that promote experimental two-stage chemical cutaneous carcinogenesis. Toward understanding their mechanism of action, this study uses whole-genome expression analysis to compare T-pro with systemic CD8+ T cells from multiple groups of tumor-bearing mice. T-pro show an overt T helper 17–like profile (high retinoic acid–related orphan receptor-(ROR)γt, IL-17A, IL-17F; low T-bet and eomesodermin), regulatory potential (high FoxP3, IL-10, Tim-3), and transcripts encoding epithelial growth factors (amphiregulin, Gro-1, Gro-2). Tricolor flow cytometry subsequently confirmed the presence of TCRβ+ CD8+ IL-17+ T cells among tumor-infiltrating lymphocytes (TILs). Moreover, a time-course analysis of independent TIL isolates from papillomas versus carcinomas exposed a clear association of the “T-pro phenotype” with malignant progression. This molecular characterization of T-pro builds a foundation for elucidating the contributions of inflammation to cutaneous carcinogenesis, and may provide useful biomarkers for cancer immunotherapy in which the widely advocated use of tumor-specific CD8+ cytolytic T cells should perhaps accommodate the cells’ potential corruption toward the T-pro phenotype. The data are also likely germane to psoriasis, in which the epidermis may be infiltrated by CD8+ IL-17-producing T cells.
Host defenses, while effecting viral clearance, contribute substantially to inflammation and disease. This double action is a substantial obstacle to the development of safe and effective vaccines against many agents, particularly respiratory syncytial virus (RSV). RSV is a common cold virus and the major cause of infantile bronchiolitis worldwide. The role of αβ T cells in RSV-driven immunopathology is well studied, but little is known about the role of “unconventional” T cells. During primary RSV challenge of BALB/c mice, some Vγ7+ γδ T cells were present; however, immunization with a live vaccinia vector expressing RSV F protein substantially enhanced Vγ4+ γδ T cell influx after RSV infection. Harvested early, these cells produced IFN-γ, TNF, and RANTES after ex vivo stimulation. By contrast, those recruited 5 days after challenge made IL-4, IL-5, and IL-10. Depletion of γδ T cells in vivo reduced lung inflammation and disease severity and slightly increased peak viral replication but did not prevent viral clearance. These studies demonstrate a novel role for γδ T cells in the development of immunopathology and cellular influx into the lungs after immunization and RSV challenge. Though a minor population, γδ T cells have a critical influence on disease and are an attractive interventional target in the alleviation of viral lung disease.
Psoriasis is an immune-mediated skin disorder that is inherited as a multifactorial trait. Linkage studies have clearly identified a primary disease susceptibility locus lying within the major histocompatibility complex (MHC), but have generated conflicting results for other genomic regions. To overcome this difficulty, we have carried out a genome-wide association scan, where we analyzed more than 408 000 SNPs in an initial sample of 318 cases and 288 controls. Outside of the MHC, we observed a single cluster of disease-associated markers, spanning 47 kb on chromosome 20q13. The analysis of two replication data sets confirmed this association, with SNP rs495337 yielding a combined P-value of 1.4 × 10−8 in an overall sample of 2679 cases and 2215 controls. Rs495337 maps to the SPATA2 transcript and is in absolute linkage disequilibrium with five SNPs lying in the adjacent ZNF313 gene (also known as RNF114). Real-time PCR experiments showed that, unlike SPATA2, ZNF313 is abundantly expressed in skin, T-lymphocytes and dendritic cells. Furthermore, an analysis of the expression data available from the Genevar database indicated that rs495337 is associated with increased ZNF313 transcripts levels (P = 0.003), suggesting that the disease susceptibility allele may be a ZNF313 regulatory variant tagged by rs495337. Homology searches indicated that ZNF313 is a paralogue of TRAC-1, an ubiquitin ligase regulating T-cell activation. We performed cell-free assays and confirmed that like TRAC-1, ZNF313 binds ubiquitin via an ubiquitin-interaction motif (UIM). These findings collectively identify a novel psoriasis susceptibility gene, with a putative role in the regulation of immune responses.
Between weaning (3 wk of age) and adulthood (7 wk of age), mice develop increased resistance to infection with Eimeria vermiformis, an abundant intestinal parasite that causes coccidiosis. This development of resistance was perturbed in T cell receptor (TCR)δ−/− mice, which at 4 wk of age remained largely susceptible to infection and prone to infection-associated dehydration. These phenotypes were rescued by the repopulation of γδ cells after adoptive transfer of lymphoid progenitors into newborn recipients. Because αβ T cells are necessary and sufficient for the protection of adult mice against E. vermiformis, the requirement for γδ cells in young mice shows a qualitative difference between the cellular immune responses operating at different ages. An important contribution toward primary immune protection in young hosts may have provided a strong selective pressure for the evolutionary conservation of γδ cells. This notwithstanding, the development of effective, pathogen-specific immunity in young mice requires αβ T cells, just as it does in adult mice.
neonatal immunology; mucosal immunology; infection; adoptive transfer; knockout mice
Epithelial tissues in which carcinomas develop often contain systemically derived T cell receptor (TCR)αβ+ cells and resident intraepithelial lymphocytes that are commonly enriched in TCRγδ+ cells. Recent studies have demonstrated that γδ cells protect the host against chemically induced cutaneous malignancy, but the role of αβ T cells has been enigmatic, with both protective and tumor-enhancing contributions being reported in different systems. This study aims to clarify the contributions of each T cell type to the regulation of squamous cell carcinoma induced in FVB mice by a two-stage regimen of 7,12-dimethylbenz[a]anthracene initiation followed by repetitive application of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate. This protocol permits one to monitor the induction of papillomas and the progression of those papillomas to carcinomas. The results show that whereas γδ cells are strongly protective, the nonredundant contributions of αβ T cells to the host's protection against papillomas are more modest. Furthermore, at both high and low doses of carcinogens, αβ T cells can contribute to rather than inhibit the progression of papillomas to carcinomas. As is likely to be the case in humans, this study also shows that the contribution of T cells to tumor immunosurveillance is regulated by modifier genes.
carcinogenesis; squamous cell carcinoma; TCR γδ; TCR αβ; immunogenetics
The function of the intraepithelial lymphocyte (IEL) network of T cell receptor (TCR) γδ+ (Vγ5+) dendritic epidermal T cells (DETC) was evaluated by examining several mouse strains genetically deficient in γδ T cells (δ−/− mice), and in δ−/− mice reconstituted with DETC or with different γδ cell subpopulations. NOD.δ−/− and FVB.δ−/− mice spontaneously developed localized, chronic dermatitis, whereas interestingly, the commonly used C57BL/6.δ−/− strain did not. Genetic analyses indicated a single autosomal recessive gene controlled the dermatitis susceptibility of NOD.δ−/− mice. Furthermore, allergic and irritant contact dermatitis reactions were exaggerated in FVB.δ−/−, but not in C57BL/6.δ−/− mice. Neither spontaneous nor augmented irritant dermatitis was observed in FVB.β−/− δ−/− mice lacking all T cells, indicating that αβ T cell–mediated inflammation is the target for γδ-mediated down-regulation. Reconstitution studies demonstrated that both spontaneous and augmented irritant dermatitis in FVB.δ−/− mice were down-regulated by Vγ5+ DETC, but not by epidermal T cells expressing other γδ TCRs. This study demonstrates that functional impairment at an epithelial interface can be specifically attributed to absence of the local TCR-γδ+ IEL subset and suggests that systemic inflammatory reactions may more generally be subject to substantial regulation by local IELs.
dermatitis; TCR γδ; mast cells; NOD; FVB
β selection is a major checkpoint in early thymocyte differentiation, mediated by successful expression of the pre-T cell receptor (TCR) comprising the TCRβ chain, CD3 proteins, and a surrogate TCRα chain, pTα. The mechanism of action of the pre-TCR is unresolved. In humans and mice, the pTα gene encodes two RNAs, pTαa, and a substantially truncated form, pTαb. This study shows that both are biologically active in their capacity to rescue multiple thymocyte defects in pTα−/− mice. Further active alleles of pTα include one that lacks both the major ectodomain and much of the long cytoplasmic tail (which is unique among antigen receptor chains), and another in which the cytoplasmic tail is substituted with the short tail of TCR Cα. Thus, very little of the pTα chain is required for function. These data support a hypothesis that the primary role of pTα is to stabilize the pre-TCR, and that much of the conserved structure of pTα probably plays a critical regulatory role.
pre-TCR; thymocyte development; α/β T cells; allelic exlusion; transgenic
Murine Lyme borreliosis, caused by infection with the spirochete Borrelia burgdorferi, results in acute arthritis and carditis that regress as a result of B. burgdorferi-specific immune responses. B. burgdorferi-specific antibodies can attenuate arthritis in mice deficient in both B cells and T cells but have no effect on carditis. Because macrophages comprise the principal immune cell in carditis, T-cell responses that augment cell-mediated immunity may be important for carditis regression. To investigate this hypothesis, we examined the course of Lyme carditis in mice selectively deficient in B cells or αβ T cells. Our results show that carditis regresses in B-cell-deficient B10.Ak mice but not in αβ T-cell-deficient mice, independently of the mouse strain background. Despite prominent macrophage infiltrates, hearts from B. burgdorferi-infected αβ T-cell-deficient mice had less mRNA for tumor necrosis factor alpha as measured by reverse transcription-PCR compared to infected control mice. Anti-inflammatory cytokine mRNA levels were equivalent. Adoptive transfer of gamma interferon-secreting CD4+ T cells into infected αβ T-cell-deficient mice promoted carditis resolution. These results show that αβ T cells can promote resolution of murine Lyme carditis and are the first demonstration of a beneficial role for CD4+ T helper 1 cells in this disease.
Because most pathogens initially challenge the body at epithelial surfaces, it is important to dissect the mechanisms that underlie T-cell responses to infected epithelial cells in vivo. The coccidian parasites of the genus Eimeria are protozoan gut pathogens that elicit a potent, protective immune response in a wide range of host species. CD4+ αβ T cells and gamma interferon (IFN-γ) are centrally implicated in the primary immunoprotective response. To define any additional requirements for the primary response and to develop a comparison between the primary and the secondary response, we have studied Eimeria infections of a broad range of genetically altered mice. We find that a full-strength primary response depends on β2-microglobulin (class I major histocompatibility complex [MHC] and class II MHC and on IFN-γ and interleukin-6 (IL-6) but not on TAP1, perforin, IL-4, Fas ligand, or inducible nitric oxide synthetase. Indeed, MHC class II-deficient and IFN-γ-deficient mice are as susceptible to primary infection as mice deficient in all αβ T cells. Strikingly, the requirements for a highly effective αβ-T-cell-driven memory response are less stringent, requiring neither IFN-γ nor IL-6 nor class I MHC. The class II MHC dependence was also reduced, with adoptively transferable immunity developing in MHC class II−/− mice. Besides the improved depiction of an immune response to a natural gut pathogen, the finding that effective memory can be elicited in the absence of primary effector responses appears to create latitude in the design of vaccine strategies.
Contact sensitivity (CS) responses to reactive hapten Ag, such as picryl chloride (PCl) or oxazolone (OX), are classical examples of T cell–mediated immune responses in vivo that are clearly subject to multifaceted regulation. There is abundant evidence that downregulation of CS may be mediated by T cells exposed to high doses of Ag. This is termed high dose Ag tolerance. To clarify the T cell types that effect CS responses and mediate their downregulation, we have undertaken studies of CS in mice congenitally deficient in specific subsets of lymphocytes. The first such studies, using αβ T cell–deficient (TCRα−/−) mice, are presented here. The results clearly show that TCRα−/− mice cannot mount CS, implicating αβ T cells as the critical CS-effector cells. However, TCRα−/− mice can, after high dose tolerance, downregulate α+/+ CS-effector T cells adoptively transferred into them. By mixing ex vivo and then adoptive cell transfers in vivo, the active downregulatory cells in tolerized α−/− mice are shown to include γδ TCR+ cells that also can downregulate interferon-γ production by the targeted CS-effector cells in vitro. Downregulation by γδ cells showed specificity for hapten, but was not restricted by the MHC. Together, these findings establish that γδ T cells cannot fulfill CS-effector functions performed by αβ T cells, but may fulfill an Ag-specific downregulatory role that may be directly comparable to reports of Ag-specific downregulation of IgE antibody responses by γδ T cells. Comparisons are likewise considered with downregulation by γδ T cells occurring in immune responses to pathogens, tumors, and allografts, and in systemic autoimmunity.