Differential Role of B Cells and IL-17 Versus IFN-γ During Early and Late Rejection of Pig Islet Xenografts in Mice.

BACKGROUND: Xenogeneic islet transplantation is an emerging therapeutic option for diabetic patients. However, immunological tolerance to xenogeneic islets remains a challenge. METHODS: The current study used a pig-to-mouse discordant xenogeneic islet transplant model to examine antidonor xenogeneic immune responses during early and late rejection and to determine experimental therapeutic interventions that promote durable pig islet xenograft survival. RESULTS: We found that during early acute rejection of pig islet xenografts, the rejecting hosts exhibited a heavy graft infiltration with B220 B cells and a robust antipig antibody production. In addition, early donor-stimulated IL-17 production, but not IFN-γ production, dominated during early acute rejection. Recipient treatment with donor apoptotic 1-ethyl-3-(3'-dimethylaminopropyl)-carbodiimide-treated splenocytes significantly inhibited antidonor IL-17 response, and when combined with B cell depletion and a short course of rapamycin led to survival of pig islet xenografts beyond 100 days in approximately 65% recipients. Interestingly, treated recipients in this model experienced late rejection between 100 and 200 days posttransplant, which coincided with B cell reconstitution and an ensuing emergence of a robust antidonor IFN-γ, but not IL-17, response. CONCLUSIONS: These findings reveal that early and late rejection of pig islet xenografts may be dominated by different immune responses and that maintenance of long-term xenogeneic tolerance will require strategies that target the temporal sequence of antixenogeneic immune responses.

Recipient Myd88 Deficiency Promotes Spontaneous Resolution of Kidney Allograft Rejection.

The myeloid differentiation protein 88 (MyD88) adapter protein is an important mediator of kidney allograft rejection, yet the precise role of MyD88 signaling in directing the host immune response toward the development of kidney allograft rejection remains unclear. Using a stringent mouse model of allogeneic kidney transplantation, we demonstrated that acute allograft rejection occurred equally in MyD88-sufficient (wild-type [WT]) and MyD88(-/-) recipients. However, MyD88 deficiency resulted in spontaneous diminution of graft infiltrating effector cells, including CD11b(-)Gr-1(+) cells and activated CD8 T cells, as well as subsequent restoration of near-normal renal graft function, leading to long-term kidney allograft acceptance. Compared with T cells from WT recipients, T cells from MyD88(-/-) recipients failed to mount a robust recall response upon donor antigen restimulation in mixed lymphocyte cultures ex vivo. Notably, exogenous IL-6 restored the proliferation rate of T cells, particularly CD8 T cells, from MyD88(-/-) recipients to the proliferation rate of cells from WT recipients. Furthermore, MyD88(-/-) T cells exhibited diminished expression of chemokine receptors, specifically CCR4 and CXCR3, and the impaired ability to accumulate in the kidney allografts despite an otherwise MyD88-sufficient environment. These results provide a mechanism linking the lack of intrinsic MyD88 signaling in T cells to the effective control of the rejection response that results in spontaneous resolution of acute rejection and long-term graft protection.

CCL22 to Activate Treg Migration and Suppress Depigmentation in Vitiligo.

In vitiligo, gradual cutaneous depigmentation and cytotoxic T-cell activity against melanocytes are accompanied by a paucity of regulatory T cells (Tregs) in vitiligo patient skin, indicating that autoimmune responses are not adequately held in check. Thus, we sought a means to repopulate patient skin with Tregs. We hypothesized that enhanced expression of CCL22 can promote Treg skin homing to suppress depigmentation. The mouse Ccl22 gene was cloned into an expression vector and resulting DNA was used for gene gun treatment. Two spontaneous depigmentation models with different kinetics of melanocyte loss were utilized, expressing tyrosinase-reactive and gp100-reactive TCR transgenes. Mice were subjected to five gene gun treatments 6 days apart, scanned for depigmentation weekly thereafter, and monitored for activation and proliferation of relevant T cells and for Treg infiltration to the skin. Significantly reduced depigmentation 2 weeks after treatment was accompanied by a markedly increased abundance of Tregs in the skin at the expense of melanocyte-reactive, TCR transgenic T cells, as well as by reduced proliferation and reduced IFN-γ production in response to cognate peptide. Continued treatment may be necessary for sustained, local immunosuppression. These findings suggest that topical CCL22 may be used for the treatment of vitiligo.

Immune responses in a mouse model of vitiligo with spontaneous epidermal de- and repigmentation.

To generate a mouse model of spontaneous epidermal depigmentation, parental h3TA2 mice, expressing both a human-derived, tyrosinase-reactive T-cell receptor on T cells and the matching HLA-A2 transgene, were crossed to keratin 14-promoter driven, stem cell factor transgenic (K14-SCF) mice with intra-epidermal melanocytes. In resulting Vitesse mice, spontaneous skin depigmentation precedes symmetrical and sharply demarcated patches of graying hair. Whereas the SCF transgene alone dictates a greater retinoic acid receptor-related orphan receptor gamma (RORγt)(+) T-cell compartment, these cells displayed markedly increased IL-17 expression within Vitesse mice. Similar to patient skin, regulatory T cells were less abundant compared with K14-SCF mice, with the exception of gradually appearing patches of repigmenting skin. The subtle repigmentation observed likely reflects resilient melanocytes that coexist with skin-infiltrating, melanocyte-reactive T cells. Similar repigmenting lesions were found in a different TCR transgenic model of vitiligo developed on an SCF transgenic background, supporting a role for SCF in repigmentation.

Preemptive donor apoptotic cell infusions induce IFN-γ-producing myeloid-derived suppressor cells for cardiac allograft protection.

We have previously shown that preemptive infusion of apoptotic donor splenocytes treated with the chemical cross-linker ethylcarbodiimide (ECDI-SPs) induces long-term allograft survival in full MHC-mismatched models of allogeneic islet and cardiac transplantation. The role of myeloid-derived suppressor cells (MDSCs) in the graft protection provided by ECDI-SPs is unclear. In this study, we demonstrate that infusions of ECDI-SPs increase two populations of CD11b(+) cells in the spleen that phenotypically resemble monocytic-like (CD11b(+)Ly6C(high)) and granulocytic-like (CD11b(+)Gr1(high)) MDSCs. Both populations suppress T cell proliferation in vitro and traffic to the cardiac allografts in vivo to mediate their protection via inhibition of local CD8 T cell accumulation and potentially also via induction and homing of regulatory T cells. Importantly, repeated treatments with ECDI-SPs induce the CD11b(+)Gr1(high) cells to produce a high level of IFN-γ and to exhibit an enhanced responsiveness to IFN-γ by expressing higher levels of downstream effector molecules ido and nos2. Consequently, neutralization of IFN-γ completely abolishes the suppressive capacity of this population. We conclude that donor ECDI-SPs induce the expansion of two populations of MDSCs important for allograft protection mediated in part by intrinsic IFN-γ-dependent mechanisms. This form of preemptive donor apoptotic cell infusions has significant potential for the therapeutic manipulation of MDSCs for transplant tolerance induction.

A quantitative increase in regulatory T cells controls development of vitiligo.

T-cell cytolytic activity targeting epidermal melanocytes is shown to cause progressive depigmentation and autoimmune vitiligo. By using the recently developed transgenic mice h3TA2 that carry T cells with a HLA-A2-restricted human tyrosinase peptide (h-Tyr)-reactive TCR and develop spontaneous vitiligo from an early age, we addressed the mechanism regulating autoimmune vitiligo. Depigmentation was significantly impaired only in IFN-γ-knockout h3TA2 mice but not in TNF-α- or perforin-knockout h3TA2 mouse strains, confirming a central role for IFN-γ in vitiligo development. In addition, regulatory T cells (Tregs) were relatively abundant in h3TA2-IFN-γ(-/-) mice, and depletion of the Treg-engaging anti-CD25 antibody fully restored the depigmentation phenotype in h3TA2-IFN-γ(-/-) mice, mediated in part through the upregulation of proinflammatory cytokines such as IL-17 and IL-22. Further therapeutic potential of Treg abundance in preventing progressive depigmentation was evaluated by adoptively transferring purified Treg or using rapamycin. Both the adoptive transfer of Tregs and the use of rapamycin induced a lasting remission of vitiligo in mice treated at the onset of disease, or in mice with established disease. This leads us to conclude that reduced regulatory responses are pivotal to the development of vitiligo in disease-prone mice, and that a quantitative increase in the Treg population may be therapeutic for vitiligo patients with active disease.

Megakaryocyte progenitors are the main APCs inducing Th17 response to lupus autoantigens and foreign antigens.

In search of autoantigen-presenting cells that prime the pathogenic autoantibody-inducing Th cells of lupus, we found that CD41(+)CD151(+) cells among Lineage(-) (Lin(-)) CD117(+) (c-Kit(+)) CX3CR1(-) splenocytes depleted of known APCs were most proficient in presenting nuclear autoantigens from apoptotic cells to induce selectively an autoimmune Th17 response in different lupus-prone mouse strains. The new APCs have properties resembling megakaryocyte and/or bipotent megakaryocyte/erythroid progenitors of bone marrow, hence they are referred to as MM cells in this study. The MM cells produce requisite cytokines, but they require contact for optimal Th17 induction upon nucleosome feeding, and can induce Th17 only before undergoing differentiation to become c-Kit(-)CD41(+) cells. The MM cells expand up to 10-fold in peripheral blood of lupus patients and 49-fold in spleens of lupus mice preceding disease activity; they accelerate lupus in vivo and break tolerance in normal mice, inducing autoimmune Th17 cells. MM cells also cause Th17 skewing to foreign Ag in normal mice without Th17-polarizing culture conditions. Several molecules in MM cells are targets for blocking of autoimmunization. This study advances our understanding of lupus pathogenesis and Th17 differentiation biology by characterizing a novel category of APC.

The histone peptide H4 71-94 alone is more effective than a cocktail of peptide epitopes in controlling lupus: immunoregulatory mechanisms.

Tolerance therapy with nucleosomal histone peptides H4(71-94), H4(16-39), or H1'(22-42) controls disease in lupus-prone SNF1 mice. It would be clinically important to determine whether a cocktail of the above epitopes would be superior. Herein, we found that compared with cocktail peptides, H4(71-94) monotherapy more effectively delayed nephritis onset, prolonged lifespan, diminished immunoglobulin G autoantibody levels, reduced autoantigen-specific Th1 and Th17 responses and frequency of T(FH) cells in spleen and the helper ability of autoimmune T cells to B cells, by inducing potent CD8 Treg cells. H4(71-94) therapy was superior in "tolerance spreading," suppressing responses to other autoepitopes, nucleosomes, and ribonucleoprotein. We also developed an in vitro assay for therapeutic peptides (potentially in humans), which showed that H4(71-94), without exogenous transforming growth factor (TGF)-ß, was efficient in inducing stable CD4(+)CD25(+)Foxp3(+) T cells by decreasing interleukin 6 and increasing TGF-ß production by dendritic cells that induced ALK5-dependent Smad-3 phosphorylation (TGF-ß signal) in target autoimmune CD4(+) T cells.

Apigenin, a non-mutagenic dietary flavonoid, suppresses lupus by inhibiting autoantigen presentation for expansion of autoreactive Th1 and Th17 cells.

INTRODUCTION: Lupus patients need alternatives to steroids and cytotoxic drugs. We recently found that apigenin, a non-mutagenic dietary flavonoid, can sensitize recurrently activated, normal human T cells to apoptosis by inhibiting nuclear factor-kappa-B (NF-kappaB)-regulated Bcl-xL, cyclooxygenase 2 (COX-2), and cellular FLICE-like inhibitory protein (c-FLIP) expression. Because sustained immune activation and hyperexpression of COX-2 and c-FLIP contribute to lupus, we treated SNF1 mice that spontaneously develop human lupus-like disease with apigenin. METHODS: SNF1 mice with established lupus-like disease were injected with 20 mg/kg of apigenin daily and then monitored for development of severe nephritis. Histopathologic changes in kidneys, IgG autoantibodies to nuclear autoantigens in serum and in cultures of splenocytes, along with nucleosome-specific T helper 1 (Th1) and Th17 responses, COX-2 expression, and apoptosis of lupus immune cells were analyzed after apigenin treatment. RESULTS: Apigenin in culture suppressed responses of Th1 and Th17 cells to major lupus autoantigen (nucleosomes) up to 98% and 92%, respectively, and inhibited the ability of lupus B cells to produce IgG class-switched anti-nuclear autoantibodies helped by these Th cells in presence of nucleosomes by up to 82%. Apigenin therapy of SNF1 mice with established lupus suppressed serum levels of pathogenic autoantibodies to nuclear antigens up to 97% and markedly delayed development of severe glomerulonephritis. Apigenin downregulated COX-2 expression in lupus T cells, B cells, and antigen-presenting cells (APCs) and caused their apoptosis. Autoantigen presentation and Th17-inducing cytokine production by dendritic cells were more sensitive to the inhibitory effect of apigenin in culture, as evident at 0.3 to 3 muM, compared with concentrations (10 to 100 microM) required for inducing apoptosis. CONCLUSIONS: Apigenin inhibits autoantigen-presenting and stimulatory functions of APCs necessary for the activation and expansion of autoreactive Th1 and Th17 cells and B cells in lupus. Apigenin also causes apoptosis of hyperactive lupus APCs and T and B cells, probably by inhibiting expression of NF-kappaB-regulated anti-apoptotic molecules, especially COX-2 and c-FLIP, which are persistently hyperexpressed by lupus immune cells. Increasing the bioavailability of dietary plant-derived COX-2 and NF-kappaB inhibitors, such as apigenin, could be valuable for suppressing inflammation in lupus and other Th17-mediated diseases like rheumatoid arthritis, Crohn disease, and psoriasis and in prevention of inflammation-based tumors overexpressing COX-2 (colon, breast).

Low-dose peptide tolerance therapy of lupus generates plasmacytoid dendritic cells that cause expansion of autoantigen-specific regulatory T cells and contraction of inflammatory Th17 cells.

Subnanomolar doses of an unaltered, naturally occurring nucleosomal histone peptide epitope, H4(71-94), when injected s.c. into lupus-prone mice, markedly prolong lifespan by generating CD4+25+ and CD8+ regulatory T cells (Treg) producing TGF-beta. The induced Treg cells suppress nuclear autoantigen-specific Th and B cells and block renal inflammation. Splenic dendritic cells (DC) captured the s.c.-injected H4(71-94) peptide rapidly and expressed a tolerogenic phenotype. The DC of the tolerized animal, especially plasmacytoid DC, produced increased amounts of TGF-beta, but diminished IL-6 on stimulation via the TLR-9 pathway by nucleosome autoantigen and other ligands; and those plasmacytoid DC blocked lupus autoimmune disease by simultaneously inducing autoantigen-specific Treg and suppressing inflammatory Th17 cells that infiltrated the kidneys of untreated lupus mice. Low-dose tolerance with H4(71-94) was effective even though the lupus immune system is spontaneously preprimed to react to the autoepitope. Thus, H4(71-94) peptide tolerance therapy that preferentially targets pathogenic autoimmune cells could spare lupus patients from chronically receiving toxic agents or global immunosuppressants and maintain remission by restoring autoantigen-specific Treg cells.

Regulatory T cells in lupus.

Naturally occurring, CD4+ CD25+ regulatory T cells that are exported from the thymus early in life play an important role in controlling organ-specific autoimmune diseases, but they may not be critical for suppressing systemic autoimmunity in lupus. On the other hand, lupus-prone subjects appear to be deficient in generation of adaptive T-regulatory cells that can be induced by various means. We review autoantigen-specific therapeutic approaches that induce such regulatory T cells. Of particular interest are TGF-ss producing CD4+ CD25+ and CD8+ regulatory T cells that are induced by low dose tolerance therapy of lupus-prone mice with nucleosomal histone peptide epitopes, administered subcutaneously in subnanomolar doses. These regulatory T cells are not only efficient in suppressing autoantigen recognition and autoantibody production, but they also inhibit migration/accumulation of pathogenic autoimmune cells in the target organ, such as the kidneys of mice prone to develop lupus nephritis. We discuss why and under what conditions such therapeutic approaches would be beneficial in lupus patients and lupus-prone subjects.

Induction of autoimmunity by immunization with hapten-modified hen egg lysozyme in hen egg lysozyme-transgenic mice.

To understand the mechanism of autoimmunity induction, hen egg lysozyme (HEL)-transgenic (Tg) C57BL/6 (B6) mice were immunized with HEL or phosphorylcholine-conjugated HEL (PC-HEL). Repeated immunization of HEL-Tg mice with native HEL failed to induce the antibody response against HEL. However, immunization with PC-HEL generated a significant anti-HEL antibody response. Immunization of the Tg mice with dominant (HEL(74-88)) or cryptic (HEL(47-61)) T-cell epitope peptide stimulated the corresponding T-cell response and similarly yielded the anti-HEL antibody response. Predominance of immunoglobulin G1 (IgG1) anti-HEL antibody response in the HEL-Tg mice and preferential IL-4 production by HEL-specific T cells suggested the dependency of the antibody response to the presence of T helper 2. HEL-Tg mice received HEL-primed B6 T cells, but not HEL-primed Tg T cells, were able to generate anti-HEL antibody response following PC-HEL immunization. The pattern and the level of epitope peptides generated by splenic antigen-presenting cells indicated that PC-HEL results in much more efficient processing as compared to HEL. These results strongly suggest that the enhancement of antigen processing by hapten (PC) conjugation to the antigen facilitates more efficient stimulation of T cells reactive to self antigen, HEL in HEL-Tg mice resulting in the production of anti-self HEL antibody.

A defect in deletion of nucleosome-specific autoimmune T cells in lupus-prone thymus: role of thymic dendritic cells.

To study central tolerance to the major product of ongoing apoptosis in the thymus, we made new lines of transgenic (Tg) mice expressing TCR of a pathogenic autoantibody-inducing Th cell that was specific for nucleosomes and its histone peptide H4(71-94). In the lupus-prone (SWR x NZB)F1 (SNF1) thymus, introduction of the lupus TCR transgene caused no deletion, but marked down-regulation of the Tg TCR and up-regulation of endogenous TCRs. Paradoxically, autoimmune disease was suppressed in the alphabetaTCR Tg SNF1 mice with induction of highly potent regulatory T cells in the periphery. By contrast, in the MHC-matched, normal (SWR x B10. D2)F1 (SBF1), or in the normal SWR backgrounds, marked deletion of transgenic thymocytes occurred. Thymic lymphoid cells of the normal or lupus-prone mice were equally susceptible to deletion by anti-CD3 Ab or irradiation. However, in the steady state, spontaneous presentation of naturally processed peptides related to the nucleosomal autoepitope was markedly greater by thymic dendritic cells (DC) from normal mice than that from lupus mice. Unmanipulated thymic DC of SNF1 mice expressed lesser amounts of MHC class II and costimulatory molecules than their normal counterparts. These results indicate that apoptotic nucleosomal autoepitopes are naturally processed and presented to developing thymocytes, and a relative deficiency in the natural display of nucleosomal autoepitopes by thymic DC occurs in lupus-prone SNF1 mice.

Gender bias in Theiler's virus-induced demyelinating disease correlates with the level of antiviral immune responses.

Multiple sclerosis is an immune-mediated disease of the CNS and shows a sex-biased distribution in which 60-75% of all cases are female. A mouse model of multiple sclerosis, Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease, also displays a gender bias. However, in the C57L/J strain of mice, males are susceptible to disease whereas females are completely resistant. In this study we determined the gender differences in the TMEV-specific immune response, which may be responsible for the gender bias in clinical disease. Our data clearly demonstrate that female C57L/J mice induce significantly higher levels of TMEV-specific neutralizing Ab as well as a stronger peripheral T cell response throughout the course of viral infection. In contrast, male mice have a higher level of TMEV-specific CD4(+) and CD8(+) T cell infiltration into the CNS as well as viral persistence. These results suggest that a higher level of the initial antiviral immune response in female mice may be able to effectively clear virus from the periphery and CNS and therefore prevent further disease manifestations. Male mice in contrast do not mount as effective an immune response, thereby allowing for eventual viral persistence in the CNS and continuous T cell expansion leading to clinical symptoms.

Very low-dose tolerance with nucleosomal peptides controls lupus and induces potent regulatory T cell subsets.

We induced very low-dose tolerance by injecting lupus prone (SWR x NZB)F1 (SNF1) mice with 1 mug nucleosomal histone peptide autoepitopes s.c. every 2 wk. The subnanomolar peptide therapy diminished autoantibody levels and prolonged life span by delaying nephritis, especially by reducing inflammatory cell reaction and infiltration in kidneys. H4(71-94) was the most effective autoepitope. Low-dose tolerance therapy induced CD8+, as well as CD4+ CD25+ regulatory T (Treg) cell subsets containing autoantigen-specific cells. These adaptive Treg cells suppressed IFN-gamma responses of pathogenic lupus T cells to nucleosomal epitopes at up to a 1:100 ratio and reduced autoantibody production up to 90-100% by inhibiting nucleosome-stimulated T cell help to nuclear autoantigen-specific B cells. Both CD4+ CD25+ and CD8+ Treg cells produced and required TGF-beta1 for immunosuppression, and were effective in suppressing lupus autoimmunity upon adoptive transfer in vivo. The CD4+ CD25+ T cells were partially cell contact dependent, but CD8+ T cells were contact independent. Thus, low-dose tolerance with highly conserved histone autoepitopes repairs a regulatory defect in systemic lupus erythematosus by generating long-lasting, TGF-beta-producing Treg cells, without causing allergic/anaphylactic reactions or generalized immunosuppression.

Identification of capsid epitopes of Theiler's virus recognized by CNS-infiltrating CD4+ T cells from virus-infected C57BL/6 mice.

Intracerebral infection of Theiler's murine encephalomyelitis virus (TMEV) induces immune-mediated demyelinating disease in some mouse strains but not in others. We report here for the first time two new predominant capsid epitopes (VP4(21-40) and VP2(201-220)) recognized by CD4+ T cells from virus-infected resistant C57BL/6 mice based on IFNgamma ELISPOT assay utilizing a 20-mer peptide library covering the entire capsid proteins. Further experiments by IFNgamma ELISPOT and flow cytometry for intracellular IFNgamma production using truncated peptides indicated that the epitope regions recognized by CNS-infiltrating CD4+ T cells are VP4(25-38) and VP2(206-220), respectively. No apparent reduction in the T cell response to these viral epitopes is seen in the CNS of IL-12- and ICAM-1-deficient C57BL/6 mice compared to those in control C57BL/6 mice, suggesting that T cell response to TMEV in the CNS is largely insensitive to the absence of these proinflammatory cytokine and adhesion molecules. Therefore, these newly defined CD4+ T cell epitopes are likely to provide an important tool to investigate the role of CD4+ T cell responses in H-2b-bearing congenic strains.

Human lupus T cells resist inactivation and escape death by upregulating COX-2.

Autoimmune T-helper cells drive pathogenic autoantibody production in systemic lupus erythematosus (SLE), but the mechanisms maintaining those T cells are unknown. Autoreactive T cells are normally eliminated by functional inactivation (anergy) and activation-induced cell death (AICD) or apoptosis through death receptor (Fas) signaling. However, mutations in the genes encoding Fas and its ligand (FasL) are rare in classical SLE. By gene microarray profiling, validated by functional and biochemical studies, we establish here that activated T cells of lupus patients resist anergy and apoptosis by markedly upregulating and sustaining cyclooxygenase-2 (COX-2) expression. Inhibition of COX-2 caused apoptosis of the anergy-resistant lupus T cells by augmenting Fas signaling and markedly decreasing the survival molecule c-FLIP (cellular homolog of viral FLICE inhibitory protein). Studies with COX-2 inhibitors and Cox-2-deficient mice confirmed that this COX-2/FLIP antiapoptosis program is used selectively by anergy-resistant lupus T cells, and not by cancer cells or other autoimmune T cells. Notably, the gene encoding COX-2 is located in a lupus-susceptibility region on chromosome 1. We also found that only some COX-2 inhibitors were able to suppress the production of pathogenic autoantibodies to DNA by causing autoimmune T-cell apoptosis, an effect that was independent of prostaglandin E(2) (PGE(2)). These findings could be useful in the design of lupus therapies.

Role of the major histocompatibility complex class II transmembrane region in antigen presentation and intracellular trafficking.

While a sorting signal in the cytoplasmic tail of the major histocompatibility complex (MHC) class II molecules is known to influence their endocytic transport, potential effects of the transmembrane (TM) domain of the MHC class II molecules on endocytic transport remain unclear. We have examined the role of the TM domain by comparing antigen-presenting functions of the wildtype (WT) I-Ab and mutant (MT) I-Ab molecule substituted in the beta-chain TM with alpha chain TM. A20 cells transfected with WT I-Ab were able to present antigen (hen egg lysozyme) better to some hybridomas, while those transfected with MT I-Ab consistently outperformed WT for other hybridomas recognizing different epitopes. This difference in antigen processing and presentation is not caused by the differences in H-2M (DM) requirement or association with Ii. The time required for processing of specific epitopes appears to be different, suggesting sequential involvement of various endocytic compartments in the antigen processing. Although both WT and MT molecules were found in the early endocytic (transferrin receptor-rich) compartments, MT molecules accumulated in these compartments in higher quantities for longer time periods. Similarly, the MT molecule is retained for a longer time period than WT in late endocytic (LAMP-1 associated) compartments. Together, our data indicate an important role of the TM domain of the MHC class II molecules in the intracellular trafficking and, consequently, antigen processing and presentation.

Preferential induction of IL-10 in APC correlates with a switch from Th1 to Th2 response following infection with a low pathogenic variant of Theiler's virus.

Theiler's murine encephalomyelitis virus induces immune-mediated demyelination in susceptible mice after intracerebral inoculation. A naturally occurring, low pathogenic Theiler's murine encephalomyelitis virus variant showed a single amino acid change within a predominant Th epitope from lysine to arginine at position 244 of VP1. This substitution is the only one present in the entire viral capsid proteins. In this paper, we demonstrate that the majority of T cells specific for VP1(233-250) and VP2(74-86) from wild-type virus-infected mice are Th1 type and these VP1-specific cells poorly recognize the variant VP1 epitope (VP1(K244R)) containing the substituted arginine. In contrast, the Th2-type T cell population specific for these epitopes predominates in variant virus-infected mice. Immunization with UV-inactivated virus or VP1 epitope peptides could not duplicate the preferential Th1/Th2 responses following viral infection. Interestingly, the major APC populations, such as dendritic cells and macrophages, produce IL-12 on exposure to the pathogenic wild-type virus, whereas they preferentially produce IL-10 in response to the low pathogenic variant virus. Thus, such a spontaneous mutant virus may have a profoundly different capability to induce Th-type responses via selective production of cytokines involved in T cell differentiation and the consequent pathogenicity of virally induced immune-mediated inflammatory diseases.

Capsid-specific cytotoxic T lymphocytes recognize three distinct H-2D(b)-restricted regions of the BeAn strain of Theiler's virus and exhibit different cytokine profiles.

The role of virus-specific cytotoxic T lymphocytes (CTL) in Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease, a viral model for multiple sclerosis, is not yet clear. To investigate the specificity and function of CTL generated in response to TMEV infection, we generated a panel of overlapping 20-mer peptides encompassing the entire capsid and leader protein region of the BeAn strain of TMEV. Binding of these peptides to H-2K(b) and H-2D(b) class I molecules of resistant mice was assessed using RMA-S cells. Several peptides displayed significant binding to H-2K(b), H-2D(b), or both. However, infiltrating cytotoxic T cells in the central nervous system of virus-infected mice preferentially lysed target cells pulsed with VP2(111-130/121-140) or VP2(121-130), a previously defined CTL epitope shared by the DA strain of TMEV and other closely related cardioviruses. In addition, at a high effector-to-target cell ratio, two additional peptides (VP2(161-180) and VP3(101-120)) sensitized target cells for cytolysis by infiltrating T cells or splenic T cells from virus-infected mice. The minimal epitopes within these peptides were defined as VP2(165-173) and VP3(110-120). Based on cytokine profiles, CTL specific for these subdominant epitopes are Tc2, in contrast to CTL for the immunodominant epitope, which are of the Tc1 type. Interestingly, CTL function towards both of these subdominant epitopes is restricted by the H-2D molecule, despite the fact that these epitopes bind both H-2K and H-2D molecules. This skewing toward an H-2D(b)-restricted response may confer resistance to TMEV-induced demyelinating disease, which is known to be associated with the H-2D genetic locus.