Vaccination of class I major histocompatibility complex (MHC)-restricted murine CD8+ cytotoxic T lymphocytes towards soluble antigens: immunostimulating-ovalbumin complexes enter the class I MHC-restricted antigen pathway and allow sensitization against the immunodominant peptide

In vivo induction of anti-ovalbumin (OVA) cytotoxic T cell responses was brought about in an MHC class I-restricted fashion by immunizing H-2^b mice with OVA in immunostimulating complexes (ISCOM). ISCOM formation with the hydrophilic soluble protein OVA was achieved upon unmasking hydrophobic protein domains by treatment at low pH values. The effector cells induced were MHC restricted, specific for the immunodominant peptide of OVA (258–276), and expressed the CD8⁺CD4^? phenotype. These results suggest that ISCOM-based vaccines may be useful to direct hydrophilic soluble antigens into the MHC class I presentation pathway in order to vaccinate CD8⁺ T lymphocytes.     

Identification of an HLA-DQ6-derived peptide recognized by mouse MHC class I H-2Db-restricted CD8+ T cells in HLA-DQ6 transgenic mice

Summary CD8⁺ T cells from C57BL/6(B6) mice show cytotoxicity to B cell blasts prepared from syngeneic transgenic mice expressing HLA-DQ6 molecules in a mouse MHC class I H-2D^b restricted manner. Although these results suggest that CD8⁺ T cells recognize peptides derived from DQ6 molecule bound to H-2D^b on target cells, no direct evidence so far has been obtained. To clarify this, we synthesized 23 peptides corresponding to DQ6α orβ chain and carrying the motifs of D^b-binding peptides, and examined their capacity to induce cytotoxicity in the CD8⁺ T cell line. We show here that DQA1-2, one of these peptides, induced cytotoxicity of the CD8⁺ T cells when this peptide was pulsed to H-2D^b expressing target cells, as efficiently as HLA-DQ6 expressing target cells did. Thus, our results suggest that DQA1-2 can be naturally processed from DQ6 molecules and recognized by the CD8⁺ T cells in the context of H-2D^b molecules. These results suggest that allogeneic HLA class II molecules are involved in the rejection not only as the ligand for T cell receptor of alloreactive CD4⁺ T cells but also as self-peptides bound to HLA class I molecules recognized by CD8⁺ T cells.     

Differential reactivity of residual CD8+ T lymphocytes in TAP1 and β2-microglobulin mutant mice

TAP1 -/- and β2-microglobulin (β2m) -/- mice (H-2^b background) express very low levels of major histocompatibility complex (MHC) class I molecules on the cell surface. Consequently these mice have low numbers of mature CD8⁺ T lymphocytes. However, TAP1 -/- mice have significantly higher numbers of CD8⁺ T cells than β2m -/- mice. Alloreactive CD8⁺ cytotoxic T lymphocyte (CTL) responses were also stronger in TAP1 -/- mice than in β2m -/- mice. Alloreactive CTL generated in TAP1 -/- and β2m -/- mice cross-react with H-2^b-expressing cells. Surprisingly, such cross-reactivity was stronger with alloreactive CTL from β2m -/- mice than with similar cells from TAP1 -/- mice. The β2m -/- mice also responded more strongly when primed with and tested against cells expressing normal levels of H-2^b MHC class I molecules. Such H-2^b-reactive CD8⁺ CTL from β2m -/- mice but not from TAP1 -/- mice also reacted with TAP1 -/- and TAP2-deficient RMA-S cells. In contrast, H-2^b-reactive CD8⁺ CTL from neither β2m -/- mice nor TAP1 -/- mice killed β2m -/- cells. In line with these results, β2m -/- mice also responded when primed and tested against TAP1 -/- cells. We conclude that the reactivity of residual CD8⁺ T cells differs between TAP1 -/- and β2m -/- mice. The MHC class I-deficient phenotype of TAP1 -/- and β2m -/- mice is not equivalent: class I expression differs between the two mouse lines with regard to quality as well as quantity. We propose that the differences observed in numbers of CD8⁺ T cells, their ability to react with alloantigens and their cross-reactivity with normal H-2^b class I are caused by differences in the expression of MHC class I ligands on selecting cells in the thymus.     

Leishmania major infection in mice primes for specific major histocompatibility complex class I-restricted CD8+ cytotoxic T cell responses

This report shows that lymphoid tissues of mice which have resolved a primary infection with Leishmania major contain parasite-specific major histocompatibility complex (MHC) class I-restricted cytolytic CD8⁺ T cell precusors that can be expanded after specific restimulation in vitro with syngeneic antigen-presenting cells pulsed with a cyanogen bromide digest of L. major. In H-2^b mice, two distinct populations of CD8⁺ T cells were identified which both lysed target cells pulsed with L. major-derived peptides but were restricted by a different H-2^b class I gene product. Interestingly, these two populations appear to recognize different parasite-derived peptides. It is noteworthy that one K°-restricted CD8⁺ T cell line was able to specifically lyse syngeneic macrophages infected with viable L. major, indicating that some L. major-derived peptides may reach the MHC class I pathway of presentation from the phagolysosomal compartment where the parasites are confined in infected macrophages. The importance of these parasite-specific MHC class I restricted cytolytic CD8⁺ T cells for the elimination of L. major by the infected host remains to be determined.     

Allogeneic recognition of class I molecules: Anti-H-2Ld repertoire of H-2b mice includes T cells recognizing mutant class II H-2b (Abm12) molecules

Two major histocompatibility complex (MHC) class I-reactive T cell clones derived from H-2^b mice, generated against the allogeneic L^d molecule, were found to recognize the H-2^b class II mutant A^bm12 molecule as well. In addition, these clones also recognize the class II A^s molecule, and display a class II-dependent reactivity to staphylococcal enterotoxin B. Neither the class I nor the class II alloreactivities of the clones were found to be dependent on other MHC molecules. Both clones express CD4+CD8^? phenotypes. The CD4 molecule appears to be involved in their class II reactivity, while little or no role for CD4 could be detected in the class I reactivity. This is the first report of a class I/class II cross-reactivity being mediated by CD4⁺ T cells. The structural basis for this cross-reactivity is discussed.     

The phenotype of H-2M-deficient mice is dependent on the MHC class II molecules expressed

For a broader view of the role of H-2M as an accessory molecule in antigen presentation, we investigated the degree to which different MHC class II isotypes and alleles depend on H-2M to function in vivo. We generated H-2M-deficient animals expressing E^{k / b} or A^k molecules in addition to the A^b molecules already present in the mutant strain, and compared the ability of the different MHC class II molecules to present antigen at the cell surface for recognition by T cells, and contribute to positive selection of CD4⁺ T cells in the thymus. Biochemical analyses were performed to assess MHC class II maturation, and to determine the peptide content of the molecules. In the absence of H-2M, E^{k / b} molecules containd a more heterogeneous set of class II-associated invariant chain peptides (CLIP) than A^b did, which, unlike A^b -CLIP complexes, were not SDS-stable. Unlike A^b molecules, both E^{k / b} and A^k efficiently presented exogenously added peptides to T cells in the absence of H-2M. In addition, epitopes from some proteins, especially those known to be invariant chain independent, were presented by A^k molecules in the mutant animals. To our surprise, expression of E^{k / b} overcame the positive selection defect observed in H-2M-deficient mice expressing A^b alone. In contrast, A^k expression did not augment positive selection of CD4⁺ T cells in the mutant animals. Some of these findings in vivo contrast significantly with findings from in vitro studies on murine MHC class II molecules in human DM-deficient cell lines.     

Major histocompatibility complex class I presentation of exogenously acquired minor alloantigens initiates skin allograft rejection

Major histocompatibility complex (MHC) class I molecules present peptides from endogenous proteins. However, in some cases class I-restricted peptides can also derive from exogenous antigens. This MHC class I exogenous presentation could be involved in minor histocompatibility antigen (mHAg)-disparate allograft rejection when donor alloantigens are not expressed in graft antigen-presenting cells (APC) that initiate the rejection mechanism. Here we addressed this question by using a skin graft experimental model where donors (H-2^b or H-2^d Tgβ-gal mice) expressed the mHAg like β-galactosidase (β-gal) in keratinocytes but not in Langerhans' cells (LC) which have an APC function. Rejection of Tgβ-gal skin by a β-gal-specific CD8 cytotoxic T lymphocyte (CTL) effector mechanism should require presentation by donor and/or recipient LC of MHC class I-restricted peptides of exogenous β-gal shed by keratinocytes. Indeed, our results showed that 1) H-2^b Tgβ-gal skin was rejected by H-2^bxs and H-2^bxd recipients; 2) rejection was mediated by β-gal-specific CD8⁺ CTL effectors; and 3) H-2^bxd mice having rejected H-2^b Tgβ-gal skin generated β-gal-specific CTL restricted by H-2^b and H-2^d class I molecules and rejected subsequently grafted H-2^d Tgβ-gal skin in an accelerated fashion, demonstrating that recipient LC have presented exogenous β-gal-derived MHC class I epitopes. These results lead to the conclusion that MHC class I exogenous presentation of donor mHAg can initiate allograft rejection.     

Analysis of intraepithelial lymphocytes from major histocompatibility complex (MHC)-deficient mice: No evidence for a role of MHC class II antigens in the positive selection of Vδ4+γδ T cells

Three-color flow cytometric analysis was carried out with intraepithelial lymphocytes from mice deficient in expression of major histocompatibility complex (MHC) antigens. These experiments were done to address the possible role of MHC class II molecules in the positive selection of Vδ4⁺ γδ T cells. By analyzing mice deficient MHC class II antigens alone or in combination with MHC class I antigens, no evidence was found for positive selection of Vδ4⁺ cells among CD8a⁺ or CD4^?CD8^? subpopulations of γδ T cell receptor-positive cells. Because V54⁺, CD8a⁺ cells were reported to be positively selected on I-E^k and hybrid I-E^k/b molecules, class II-deficient animals were crossed with I-E^k transgenic mice and progeny examined for Vδ4 expression. Again, no evidence for positive selection was found. Interestingly, in MHC class I-deficient animals, the total number of γδ T cells was about twofold higher than in control and MHC class II-deficient mice and the proportion of V8δ-expressing cells was correspondingly decreased. Taken together, these results cast doubt on a major role for conventional MHC antigens in shaping the γδ T cell repertoire of intraepithelial lymphocytes.     

Murine CD8+ T suppressors against mycobacterial 65-kDa antigen compete for IL-2 and show lack of major histocompatibility complex-imposed restriction specificity in antigen recognition

The mechanism of antigen-specific suppression and reasons for aberrant major histocompatibility complex (MHC) class II restriction mediated by CD8⁺ T cells was investigated in a previously reported murine model of immunosuppression, generated by intraperitoneal priming with Mycobacterium vaccae. Both the CD4⁺ T helper cells (T_h) and CD8⁺ T supressor cell (T_s) of M.vaccae-primed mice recognized the 65-kDa antigen of the bacillus, presented by I-A and I-E, respectively. The CD8⁺ T_s could inhibit non-antigen-specific proliferation of primed CD4⁺ T cells induced by the exogenously added interleukin (IL)-2 (concanvalin A-stimulated culture supernatant). For inhibition, the T_s had to be activated by the 65-kDa antigen. The degree of inhibition was dependent upon the amount of added IL-2 and the relative numbers of primed CD8⁺ and CD4⁺ T cells. On incubation with antigen-presenting cells, and the 65-kDa antigen, the primed CD8⁺ T cells absorbed IL-2 as efficiently as primed CD4⁺ T cells. Based on this, it was concluded that the primed CD8⁺ T cells induced suppression by competition for IL-2. Employing the same model, the MHC restriction of recognition of the suppressor epitope of the 65-kDa antigen by the CD8⁺ T_s was investigated. The epitopes presented by diverse MHC class II molecules, such as self I-A, I-E and even allogeneic I-E were similar, because they were recognized by the same population of primed CD8⁺ T_s. Further, immunization of C57BL/6 mice with Ltk-cells expressing H-2 D^kK^k alloantigens, stimulated CD8⁺ T cells capable of recognizing M.vaccae 65-kDa antigen. Based on these data, it was proposed that recognition of the suppressor epitope of the 65-kDa antigen by the primed CD8⁺ T_s exhibits lack of restriction specificity imposed by MHC diversity.     

Assessment of alloreactive T cell subpopulations of aged mice in vivo. CD4+ but not CD8+ T cell-mediated rejection response declines with advanced age

The present investigation explored age-related alterations in T cell populations mediating allospecific responses in vivo. Healthy aged and young H-2^b and H-2^bxH-2^k mice were engrafted with major histocompatibility complex (MHC) class II-disparate bm12 skin, rejection of which requires CD4⁺ T cells, and MHC class I-disparate bm1 skin, rejection of which requires CD8⁺ T cells. Aged mice of both genders exhibited prolonged survival of bm12 skin grafts relative to their young counterparts but rejected bm1 skin grafts at a rate equivalent to that of young mice. Consistent with prolonged survival of bm12 skin grafts, markedly diminished levels of Ia^bm12 CTL activity were elicited from T cells of aged mice in vitro. However, no such decline was observed in the level of K^bm1 CTL from T cells of aged mice. The alterations in Ia^bm12 allospecific responses were not attributable to quantitative changes in CD4⁺ T cells of aged mice, and addition of soluble T cell helper factors to response cultures of aged mice did not augment Ia^bm12 cytotoxic T lymphocytes activity. These data demonstrate that aging fundamentally affects CD4⁺ T cell-mediated allospecific responses particularly in vivo, and that deficient generation of soluble T cell helper factors alone cannot explain this deficit.     

Major histocompatibility complex class I-restricted CD8+ T cells and class II-restricted CD4+ T cells,respectively, mediate and regulate contact sensitivity to dinitrofluorobenzene

Contact sensitivity (CS) is a form of delayed-type hypersensitivity to haptens applied epicutaneously and is thought to be mediated, like classical delayed-type hypersensitivity responses, by CD4⁺ T helper-1 cells. The aim of this study was to identify the effector T cells involved in CS. We studied CS to the strongly sensitizing hapten dinitrofluorobenzene (DNFB) in mice rendered deficient by homologous recombination in either major histocompatibility complex (MHC) class I, MHC class II, or both, and which exhibited deficiencies in, respectively, CD8⁺, CD4⁺, or both, T cells. MHC class I single-deficient and MHC class I/class II double-deficient mice, both of which have a drastic reduction in the number of CD8⁺ T cells, were unable to mount a CS response to DNFB. In contrast, both MHC class II-deficient mice and normal mice treated with an anti-CD4 monoclonal antibody (mAb) developed exaggerated and persistent responses relative to heterozygous control littermates. Furthermore, anti-CD8 mAb depletion of class II-deficient mice totally abolished their ability to mount an inflammatory response to DNFB. Removal of residual CD4⁺ T cells in class II-deficient mice by anti-CD4 mAb treatment did not diminish the intensity of CS. These data clearly demonstrate that class I-restricted CD8⁺ T cells are sufficient for the induction of CS to DNFB, and further support the idea that MHC class II-restricted CD4⁺ T cells down-regulate this inflammatory response.     

Characterization of host CD4+ T lymphocytes in mice neonatally tolerized to alloantigens

BALB/c mice injected at birth with semi-allogeneic F1 spleen cells become tolerant to alloantigens as shown by their CTL unresponsiveness to the corresponding alloantigen and the persistence of donor F1 cells into the BALB/c host. Moreover, these mice develop a transient systemic lupus erythematosis-like autoimmune syndrome characterized by splenomegaly, glomerulonephritis, thrombocytopenia and abnormal serological findings, such as several autoantibodies and IgG1 hypergammaglobulinemia. Recent studies done in our laboratory have shown that donor F1 B cells persisting in the host are responsible for the production of autoantibodies and must be activated in vivo by the host CD4⁺ T lymphocytes in a MHC class II-restricted fashion. In the present work, we have focused our attention on the ability of splenic CD4⁺ T cells recovered at different periods from BALB/c mice injected at birth with (CBA/Ca × BALB. Igh^b) Fl spleen cells to interact with and activate F1 semi-allogeneic spleen cells in vitro. We show that (i) only CD4⁺ T cells from 2- and 3-week-old tolerant BALB/c mice preferentially produce IL-4 and IL-5 in response to a F1 semi-allogeneic in vitro stimulation, (ii) CD4⁺ T cells purified from 3-week-old tolerant BALB/c mice are able to induce in vitro IgG and IgM production by F1 B cells. Taken together, these results strongly suggest that host CD4+ T cells, belonging to the TH2 subset progressively lose their reactivity towards the F1 semi-allogeneic persistent B cells, reaching a state of unresponsiveness that correlates with the disappearance of serum autoantibodies and autoimmune pathology.     

Clearance of Sendai virus by CD8+ T cells requires direct targeting to virus-infected epithelium

Minimal numbers of CD8⁺ T cells are found in bronchoalveolar lavage (BAL) populations recovered from Sendai virus-infected mice that are homozygous (?/?) for β2-microglobulin (β2-m) gene disruption. The prevalence of the CD8⁺ set was substantially increased in the pneumonic lungs of 8?12-week radiation chimeras made using substantially class I major histocompatibility complex (MHC) glycoprotein-negative β2-m (?/?) recipients and normal β2-m (+/+) bone marrow. Even so, the CD8⁺ (but not the CD4⁺) lymphocyte counts were still much lower than in the (+/+)→(+/+) controls. The (+/+)→(+/+) and (+/+)→(?/?) chimeras cleared Sendai virus and potent virus-immune CD8⁺ cytotoxic T lymphocytes (CTL) specific for H-2K^b + viral nucleoprotein peptide were found in the BAL from both groups. However, following in vivo depletion of the CD4⁺ population, only the (+/+)→(+/+) mice were able to deal with the infection. Similarly, adoptively transferred, H-2K^b-restricted CD8⁺ T cells from previously-primed (+/+) mice also failed to clear virus from the lungs of (+/+)→(?/?) chimeras infected within 2 weeks of reconstitution with bone marrow, though they were effective in the (+/+)→(+/+) controls. Sendai virus-immune CD8⁺ T cells are thus unable to eliminate virus-infected β2-m (?/?) lung epithelial cells that might be thought to be expressing very small amounts of either isolated class I heavy chain, or class I MHC glycoprotein that has bound β2-m derived from β2-m (+/+) T cells or macrophages present in the pneumonic lung. Furthermore, the CD8⁺ CTL that are being exposed to β2-m (+/+) stimulators in the BAL population cannot operate in some bystander mode to clear virus from respiratory epithelium.     

TAP1-deficient mice select a CD8+ T cell repertoire that displays both diversity and peptide specificity

Mice deficient in the gene encoding the transporter associated with antigen processing 1 (TAP1) are defective in providing major histocompatibility complex (MHC) class I molecules with cytosolic peptides. Consequently, these mice express reduced levels of MHC class I glycoproteins on the cell surface, and have reduced numbers of CD8⁺ T cells in the periphery. In the present study, we have addressed the diversity and specificity of the peripheral CD8⁺ T cell population in TAP1 -/- mice. CD8⁺ T cells were polyclonal with regard to T cell receptor (TCR) Vβ expression. Overall, Vβ usage in TAP1 -/- mice appeared to be very similar to that in wild-type mice, with significantly reduced levels of Vβ5.1/5.2-expressing CD8⁺ T cells as the only clear exception. This polyclonal population of CD8⁺ T cells readily mounted epitope-specific CTL responses against four out of five well-defined MHC class I-restricted peptides. In contrast to allospecific CTL, peptide-specific CTL from TAP1 -/- mice did not cross-react on cells expressing normal levels of H-2^b class I. The present results demonstrate that a polyclonal CD8⁺ T cell repertoire, displaying both diversity and peptide specificity, is positively selected in mice devoid of a functional peptide transporter. These observations imply that TAP-dependent peptides are not absolutely required for positive selection of a functionally diverse repertoire of CD8⁺ T cells.     

Spontaneous breakdown of T cell tolerance in the mouse lgG2ab-suppression model despite long-term tolerogenesis since the perinatal period

T celt-induced fgG2a^b allotype suppression provides a physiologicalmodel for the study of T cell responsiveness or tolerance tothis Ig allotype. Normal, untreated mice of the lgh^a haplotypepossess a basic and easily amplifiable T cell reactivity againstthe expression of lgG2a^b, while their lgh^b congenic mice producesubstantial levels of this Ig and thereby are tolerant to thisself-protein antigen. Therefore, the involved TCR repertoirein lgha and lgh^b congenic mice is different. We have previouslyshown, in lgh^b and Igh^a/b mice perinatally deprived of lgG2a^bexpression, that T lymphocytes bearing anti-lgG2a^b TCR can emergeand induce an autoimmune suppression of lgG2ab. Correlatively,full and lgG2a^b-specific T cell tolerance can be induced inlgh^a mice by their perinatal exposure to this Ig allotype. Inthis physiological model, which involves neither superantigensnor TCR-transgenic T cells, the responsive or tolerant statein lgh^a mice is assessed in vivo by the capacity to induce ornot a T CD8⁺-dependent suppression of lgG2a^b allotype productionin Igh^a/b recipients of these cells. Taking advantage of thissystem, we were able to demonstrate here that, over the longterm, this perinatally induced, lgG2a^b-specific T cell tolerancewas not definitively acquired, and that a spontaneous and totaltolerance breakdown was observed by the age of 6 months. Furthermore,we showed that perinatal followed by prolonged tolerogen treatmentsup to 3, 6 and even 9 months of age were no longer sufficientto assure definitive T cell tolerance acquisition to lgG2a^b,as the T cell suppression-induction capacity of lgha mice waspartially and then entirely restored 3–6 months afterthe end of the tolerogen administration.     

Th1 clones that suppress IgG2ab specifically recognize an allopeptide determinant comprising residues 435–451 of γ2ab

We have previously reported that γ2a^b/I-A^d-specific Th1 clones from BALB/c mice (γ2a^a, H-2^d) mediated a long-lasting, selective suppression of serum IgG2a^b levels when transferred to newborn (BALB/c X B10.D2)F₁ (γ2^a/b, H-2^d) mice (Bartnes, K. and Hannestad, K. Eur. J. Immunol. 1991. 21: 2365). We here analyze the peptide specificity of hybridomas derived from two suppressive T cell clones. The shortest synthetic peptide with optimal antigenicity comprises γ2a^b residues 435–451 (Kabat numbering). The determinant core encompasses the γ2a^b 440–446 (KLRVQKS) sequence which contains an I-A^d allele-specific motif. Challenge with single amino acid-substituted γ2a^b 435–447 analogs revealed that residues K⁴⁴⁰, R⁴⁴² and K⁴⁴⁵ which are shared by the autologous and allogeneic γ2a, as well as residues Q⁴⁴⁴ and S⁴⁴⁶ which represent allogeneic differences, are critical for recognition. We obtained evidence that K⁴⁴⁰, R⁴⁴² and Q⁴⁴⁴ are epitope residues, while K⁴⁴⁵ and S⁴⁴⁶ contribute to anchoring of the peptide to I-A^d. Amino acids located outside of the core also influence antigenicity, the most striking effect being a 340–870-fold augmentation of potency when γ2a^b 437–451 is extended by F⁴³⁶. IgG2a^b required processing in order to stimulate the hybridomas. The data support the contention that the Th1 clones specific for Fc of γ2a^b mediated IgG2a^b suppression by cognate interaction with sIgG2a^b+ B cells that presented a Cγ2a^b peptide(s) derived from their endogenous Ig on major histocompatibility complex class II. The T cells cross-reacted weakly with peptide 435–451 of the autologous γ2a^a allotype. This opens the possibility that self-peptides from Ig C regions can target B cells for regulatory interactions with autologous Th cells.     

Expression of class II,but not class I,major histocompatibility complex molecules is required for granuloma formation in infection with Schistosoma mansoni

Previous studies have suggested that granulomatous inflammation in schistosomiasis is mediated by CD4⁺ T helper lymphocytes sensitized to parasite egg antigens. However, CD8⁺ T cells have also frequently been associated with the immune response to schistosome eggs. To examine more precisely the role of CD4⁺ and CD8⁺ T cells in the pathology of the schistosomal infection, we used mice with targeted mutations in major histocompatibility complex (MHC) class II or class I molecules. These mutations lead, respectively, to the virtual absence of CD4⁺ and CD8⁺ T cells. The results clearly show that schistosome-infected MHC class II mutant mice failed to form granulomas around parasite eggs. In contrast, infected MHC class I mutant mice displayed characteristic granulomatous lesions that were comparable to those in wild-type control mice. Moreover, lymphoid cells from MHC class II mutant mice were unable to react to egg antigens with either proliferative or cytokine [interferon-gamma, interleukin (IL)-4, IL-10] responses; nor were they able to present egg antigens to specifically sensitized CD4⁺ T helper cells from infected syngeneic control mice. By comparison, cells from MHC class I mutant mice exercised all these functions in a manner comparable with those from wild-type controls. These observations clearly demonstrate that schistosomal egg granulomas are mediated by MHC class II-restricted CD4⁺ T helper cells. They also suggest that CD8⁺ T cells do not become sensitized to egg antigens and play little role, if any, in the pathogenesis of schistosomiasis.     

Analysis of graft-versus-host disease (GVHD) and graft rejection using MHC class I-deficient mice

GVHD is a major complication in allogeneic bone marrow transplantation (BMT). MHC class I mismatching increases GVHD, but in MHC-matched BMT minor histocompatibility antigens (mH) presented by MHC class I result in significant GVHD. To examine the modification of GVHD in the absence of cell surface MHC class I molecules, β₂-microglobulin-deficient mice (β₂m-/-) were used as allogeneic BMT recipients in MHC- and mH-mismatched transplants. β₂m-/- mice accepted MHC class I-expressing BM grafts and developed significant GVHD. MHC (H-2)-mismatched recipients developed acute lethal GVHD. In contrast, animals transplanted across mH barriers developed indolent chronic disease that was eventually fatal. Engrafted splenic T cells in all β₂m-/- recipients were predominantly CD3⁺ αβ TCR⁺ CD4⁺ cells (15–20% of all splenocytes). In contrast, CD8⁺ cells engrafted in very small numbers (1–5%) irrespective of the degree of MHC mismatching. T cells proliferated against recipient strain antigens and recognized recipient strain targets in cytolytic assays. Cytolysis was blocked by anti-MHC class II but not anti-CD8 or anti-MHC class I monoclonal antibodies (MoAbs). Cytolytic CD4⁺ T cells induced and maintained GVHD in mH-mismatched β₂m-/- mice, supporting endogenous mH presentation solely by MHC class II. Conversely, haematopoietic β₂m-/- cells were unable to engraft in normal MHC-matched recipients, presumably due to natural killer (NK)-mediated rejection of class I-negative cells. Donor-derived lymphokine-activated killer cells (LAK) were unable to overcome graft rejection (GR) and support engraftment.     

Non-tolerant B cells cause autoimmunity in anti-CD8 IgG2a-transgenic mice

Using a pair of γ2a/x immunoglobulin genes, transgenic mice were generated to study tolerance induction in B cells that express IgG2a autoantibodies. The transgenic IgG2a specifically binds CD8 α chains of the CD8.2 allotype expressed on the surface of CD8⁺ T cells, but not CD8 molecules expressed by the CD8.1 allele. Thus, IgG2a transgenic mice expressing the CD8.1 allele were used as controls to monitor B cell development and mice expressing CD8.2 were used to study B cell tolerance. Both types of mice showed transgenic γ2a expression on the surface of B cells. Expression of endogenous heavy chain alleles was strongly inhibited in immature B cell subsets, whereas mature B cells co-expressed transgenic γ2a and endogenous IgM/D. The transgenic x chain expression leads only to partial allelic exclusion of endogenous light chains. B cells that express high levels of transgenic CD8.2-specific IgG2a were identified using soluble CD8-Ig. In CD8.1⁺ and in CD8.2⁺ mice, we found no differences in expression and maturation of transgenic anti-CD8.2 IgG2a⁺ B cells. High levels of serum anti-CD8.2 IgG2a antibodies led to the elimination of CD8⁺ T cells, causing a severe defect in cytotoxic immune responses. These results show that tolerance induction is incomplete in the CD8.2⁺ mice, either because IgG2a⁺ B cells are resistant to censoring mechanisms or because the secreted CD8-specific IgG2a antibodies render the CD8 autoantigen inaccessible to the B cells. This contrasts strongly with the efficient induction of B cell tolerance in mice expressing anti-CD8.2 IgM autoantibodies.     

SPECIFICITY OF ANTI-H-2 CLASS I ANTIBODIES INDUCED BY SYNGENEIC IMMUNIZATION WITH SENDAI VIRUS-TREATED CELLS IS REGULATED BY THE MOUSE MHC AND VIRAL ANTIGENS. NO EVIDENCE FOR MHC-RESTRICTED VIRUS- SPECIFIC ANTIBODIES

In a previous study, we searched for Sendai virus (SV)-specific antibodies that were restricted in their binding by self-major histocompatability complex (MHC) antigens. In C57BL/6 (B6; H-2^b) mice, most of the sera obtained after i.p. injections with syngeneic SV-coated (SV⁺) spleen cells contained auto- and alloreactive lymphocytotoxic antibodies directed against H-2 class I molecules, but no viral-specific, MHC-restricted antibodies. Here we report that syngeneic immunization with SV⁺ cells regularly induced H-2-specific antibodies in various mouse strains. From a total of 12 strains tested, only the B10.S (H-2^s) strain appeared to be a low responder. The immune responses are of two types: (i) mice of some strains produce autoreactive antibodies and a broad variety of alloreactive antibodies; and (ii) mice of some strains produce only narrow or widely alloreactive antibodies. Because most of the strains differ only in the H-2 region, the patterns observed are regulated by the MHC. To locate the genes involved in the induction of H-2-specific antibodies more precisely, two B6 mutant strains, bml (K^b mutant) and bm13 (D^b mutant), were immunized with syngeneic SV⁺ cells. The results suggest that the H-2D^b region plays an important role in the induction and specificity of the lymphocytotoxic H-2 class I-specific antibodies present in sera of H-2^b mice after syngeneic immunization with SV⁺ cells.