Lymphocyte recruitment and protective efficacy against pulmonary mycobacterial infection are independent of the route of prior Mycobacterium bovis BCG immunization

Mycobacterium tuberculosis infects humans through the lung, and immunity to this chronic infection is mediated primarily by CD4(+) T lymphocytes. Recently we have demonstrated that the recruitment of lymphocytes to the lung during primary aerosol M. tuberculosis infection in mice occurs predominantly through the interaction of alpha(4)beta(1) integrin on CD4(+) T cells and vascular cell adhesion molecule-1 on the pulmonary endothelium. To investigate the effect of route of immunization with Mycobacterium bovis BCG on the pattern of T-cell recruitment to the lung, we have analyzed the differences in expression of integrins on activated memory CD4(+) T cells infiltrating the lung following primary BCG immunization by aerosol, intravenous, and subcutaneous routes and after subsequent aerosol challenge with M. tuberculosis. There were marked differences in the patterns of recruitment of activated CD4(+) T cells to the lung following primary immunization by the three routes. Expansion of CD44(hi) CD62L(low) CD4(+) T cells in the lung occurred following aerosol and intravenous BCG immunizations, and the lymphocyte recruitment was proportional to the pulmonary bacterial load. The majority of infiltrating CD4(+) T cells expressed alpha(4)beta(1) integrin. On subsequent exposure to aerosol BCG rapid expansion of gamma interferon-secreting alpha(4)beta(1)(+) CD4(+) T cells occurred to the same extent in all immunized mice, regardless of the route of immunization. Similar expansion of alpha(4)beta(1)(+) CD4(+) memory T cells occurred following M. tuberculosis challenge. The three routes of BCG immunization resulted in the same level of protection against aerosol M. tuberculosis or BCG challenge in both the lungs and spleen. Therefore, recruitment of effector T lymphocytes and protective efficacy against pulmonary mycobacterial infection are independent of the route of prior BCG immunization.

MHC class I molecules on adenovirus E1A-expressing tumor cells inhibit NK cell killing but not NK cell-mediated tumor rejection

Expression of adenovirus E1A gene products in tumor cells enhances NK cell lysis in vitro and NK-mediated rejection in vivo, despite increasing class I molecules on tumor cells. It is unclear why the increased expression of MHC class I molecules does not appear to confer resistance to killing by NK cells. One possibility is the unique capacity of E1A to sensitize cells to multiple NK cell killing mechanisms including perforin/granzyme, Fas ligand, tumor necrosis factor-alpha and TRAIL. To examine this issue, MCA-102-E1A tumor cells (H-2(b)) that express E1A and are NK sensitive were transfected with H-2D(d), the ligand for the NK inhibitory receptor, Ly49A. Expression of H-2D(d) molecules by MCA-102-E1A cells protected them from lysis by a Ly49A(+) NK cell clone and Ly49A(+) NK cells isolated from C57BL/6 nude mice. In contrast, NK cell-mediated rejection of MCA-102-E1A tumor cells was not inhibited by the expression of H-2D(d) molecules, nor was killing by polyclonal populations of NK cells isolated from C57BL/6-nude mice. H-2D(d) interacts with several inhibitory Ly49 receptors that are non-clonally expressed on NK cells in C57BL/6 mice: Ly49A (20% of NK cells), Ly49G2 (54% of NK cells) and Ly49C/I (47% of NK cells). Our data indicate that while E1A sensitizes cells to NK cell killing, it does not interfere with signal transduction by inhibitory NK receptors. Therefore, a small population of NK cells that do not express Ly49A, Ly49G2 or Ly49C/I inhibitory receptors are likely responsible for the rejection of MCA-102-E1A-D(d) tumor cells in vivo.

Relative resistance to nasally induced tolerance in non-obese diabetic mice but not other I-A(g7)-expressing mouse strains

I-A(g7) is a unique class II MHC molecule that is clearly associated with autoimmune diabetes in non-obese diabetic (NOD) mice. To determine if I-A(g7) is defective in its ability to deliver tolerogenic signals in vivo, H-2(g7) mice were nasally pretreated with antigen, prior to immunization, to induce antigen-specific regulation. Nasally pretreated NOR (H-2(g7)) and (NON).NOD (H-2(g7)) congenic mice showed responses similar to those of NON (H-2(nb1)), BALB/c (H-2(d)) and B10.PL (H-2(u)) mice-a reduced recall response and a deviated T(h) cytokine profile. However, we found that NOD (H-2(g7)) mice are comparatively resistant to immunological tolerance induced by nasal pretreatment, such that at the usually effective dose no significant reduction was seen in the proliferative recall responses to nominal antigen after immunization. (NOD x BALB/c)F(1) (H-2(g7/d)) and (NOD x NOR)F(1) (H-2(g7)) mice were similarly resistant to nasal-induced tolerance, although significantly higher nasal doses of antigen were able to overcome the resistance in NOD and F(1) mice. Interestingly, activated NOD T cells were resistant to cell death induced by re-stimulation with plate-bound anti-CD3. These results demonstrate that activated T cells in NOD mice are defective in their ability to respond to regulatory signals delivered in vivo or in vitro. Furthermore, NOD T cells have an increased resistance to tolerance induced by I-A(g7)-dependent (antigen) or I-A(g7)-independent (anti-CD3) mechanisms. Thus, while I-A(g7) may contribute to insulin-dependent diabetes mellitus by selecting a particular repertoire of self-reactive T cell clones, additional defects in the peripheral T cells themselves are required to allow the expansion of diabetogenic clones and the development of autoimmune disease.

Cutting edge: culture with high doses of viral peptide induces previously unprimed CD8(+) T cells to produce cytokine

Culturing naive T cells with 50 microM selected HIV-1 envelope peptides for 6 days in the presence of IL-2 drives the emergence of a substantial CD8(+) population that secretes IFN-gamma following short-term stimulation with 1 microM peptide. This response is H-2K(b) restricted, epitope specific, and requires the continuing presence of peptide. The same effect was found for known H-2D(b)-restricted peptides from two influenza virus proteins. The great majority of these influenza-specific CD8(+)IFN-gamma(+) T cells neither stained with the cognate tetramer nor expressed the TCR Vbeta bias that is characteristic of the CD8(+) set expanded in vivo during an infection. Thus, multipoint binding of low affinity TCRs on naive CD8(+) T cells can drive peptide-specific cytokine production. However, at least for two influenza-derived epitopes, the avidity of the TCR-MHC peptide interaction appears to be insufficient to stabilize a tetrameric complex of MHC class I glycoprotein plus peptide on the lymphocyte surface.

Ly49A allelic variation and MHC class I specificity

The Ly49 family of natural killer (NK) cell receptors is encoded by a polygenic genetic locus. Allelic forms have been described and their expression appears to be regulated. The best-characterized Ly49 molecule, the C57BL/6 form of Ly49A, is an NK cell inhibitory receptor that binds H2Dd. To determine whether differences between Ly49a alleles may have functional consequences, allelic variants of Ly49a were cloned from several inbred mouse strains. Stable transfectants expressing each Ly49a allelic variant were generated and tested for reactivity with a panel of monoclonal antibodies (mAbs A1, JR9.318, YE1/32, and YE1/48) that recognize the C57BL/6 form of Ly49A. Binding to H2Dd was also assessed using fluorescently labeled H2Dd tetramers. Furthermore, cytotoxicity assays were performed using anti-Ly49A mAb-separated interleukin-2-activated NK cells. We show that despite binding to fluorescently labeled H2Dd tetramers, the Ly49A+ NK cells from representative mouse strains displayed significantly different degrees of inhibition with H2Dd targets. These results can be interpreted in the light of recent structural data on the Ly49A-H2Dd complex. Thus, the Ly49 family displays functionally significant allelic polymorphism which adds to the repertoire of NK cell receptors.

Immunostimulatory DNA-based vaccines elicit multifaceted immune responses against HIV at systemic and mucosal sites

Immunostimulatory DNA sequences (ISS, also known as CpG motifs) are pathogen-associated molecular patterns that are potent stimulators of innate immunity. We tested the ability of ISS to act as an immunostimulatory pathogen-associated molecular pattern in a model HIV vaccine using gp120 envelope protein as the Ag. Mice immunized with gp120 and ISS, or a gp120:ISS conjugate, developed gp120-specific immune responses which included: 1) Ab production; 2) a Th1-biased cytokine response; 3) the secretion of beta-chemokines, which are known to inhibit the use of the CCR5 coreceptor by HIV; 4) CTL activity; 5) mucosal immune responses; and 6) CD8 T cell responses that were independent of CD4 T cell help. Based on these results, ISS-based immunization holds promise for the development of an effective preventive and therapeutic HIV vaccine.

Genetic control of collagen-induced arthritis in a cross with NOD and C57BL/10 mice is dependent on gene regions encoding complement factor 5 and FcgammaRIIb and is not associated with loci controlling diabetes

The nonobese diabetic (NOD) mouse spontaneously develops autoimmune-mediated diseases such as diabetes and Sjögren's syndrome. To investigate whether NOD genes also promote autoimmune-mediated arthritis we established a NOD strain with an MHC class II fragment containing the A(q) class II gene predisposing for collagen induced arthritis (NOD.Q). However, this mouse was resistant to arthritis in contrast to other A(q) expressing strains such as B10.Q and DBA/1. To determine the major resistance factor/s, a genetic analysis was performed. (NOD.Q x B10.Q)F1 mice were resistant, whereas 27% of the (NOD.Q x B10.Q)F2 mice developed severe arthritis. Genetic mapping of 353 F2 mice revealed two loci associated with arthritis. One locus was found on chromosome 2 (LOD score 9.8), at the location of the complement factor 5 (C5) gene. The susceptibility allele was from B10.Q, which contains a productive C5 encoding gene in contrast to NOD.Q. The other significant locus was found on chromosome 1 (LOD score 5.6) close to the Fc-gamma receptor IIb gene, where NOD carried the susceptible allele. An interaction between the two loci was observed, indicating that they operate on the same or on interacting pathways. The genetic control of arthritis is unique in comparison to diabetes, since none of these loci have been identified in analysis of diabetes susceptibility.

Phenotype, immunological reactivity and cytokine production profile of Peyer's patch cells from mice immunized orally with allogeneic cells

Mice of inbred strain BALB/c were immunized orally for 10 consecutive days with fresh spleen cells from allogeneic C57BL/10 (B10) donors. The immunized mice displayed significant allotransplantation immunity in vivo as demonstrated by resistance to the growth of allogeneic tumours induced by high doses of tumour cells. No significant changes in the proportion of the major T cell subsets in PP of immunized mice were found 1 or 7 days after the last immunization dose. However, PP cells from orally immunized mice displayed stronger proliferative response after stimulation with cells used for oral immunization than the cells from control animals. Similarly, after stimulation in vitro with specific alloantigens, PP cells from orally immunized mice produced more IFN-gamma than the cells from control recipients. On the contrary, the production of IL-4 was significantly decreased in the immunized mice. The production of IL-2 by PP cells after oral immunization was not significantly changed and IL-10 was only slightly increased. The results thus show that oral immunization with allogeneic cells induces systemic transplantation immunity which can be demonstrated already in Peyer's patches by increased cell proliferation after immunization with specific alloantigens and by changes in cytokine production.

Role of lymphoid cells in age-related change of susceptibility to Friend leukemia virus-induced leukemia

Susceptibility for Friend leukemia virus (FLV)-induced leukemogenesis was examined in the C3H/He (C3H)-->C57BL/6 (B6) radiation bone marrow chimeras of various age groups, and the effect of aging of host mice on the susceptibility was determined. The bone marrow chimera system provided the various age of FLV-resistant host mice (B6) possessing the same age of FLV-susceptible target cells from C3H mice. Using this system, we could determine the aging effect on the host resistancy against FLV without an influence of the aging effect on target cells. First, the young C3H-->young B6 chimeras and young C3H-->old B6 chimeras were compared. The young-->old chimeras were more susceptible to FLV-induced acute disease than the young-->young chimeras. The spleen CD4+ as well as CD8+ T cells were reduced in young-->old chimeras compared with young-->young chimeras. Similarly, the old C3H-->old B6 chimeras were more susceptible than old-->young chimeras and revealed the lower CD4+ T cell ratio in the spleen. Discussion was made on the possible implication of these findings on the role of T cells in age-related change of resistance to FLV-induced leukemogenesis.

Inducing protective antibodies against ring-infected erythrocyte surface peptide antigen of Plasmodium falciparum using immunostimulating complex (ISCOMs) delivery

In the present study, synthetic peptides (EENVEHDA)2 [(oc)2] and (DDEHVEEPTVA)2 [(un)2] of ring-infected erythrocyte surface antigen (RESA) of Plasmodlium filciparum were linked with palmitic acid and entrapped in immunostimulating complexes (ISCOMs). The immunogenicity of the peptide(s) and mixture of peptides were studied in mice with different genetic background. Peptide(s) entrapped in ISCOMs using a low-dose immunization strategy generated high-titer as well as high-affinity antibodies. Interestingly, no genetic restriction of the immune response was observed in any of the strains studied. The IgG subclass pattern with the peptide(s) showed predominately IgG2a/2b isotypes, while with the mixed peptide formulation, (un)2-specific IgG isotype pattern showed induction of both IgG1 and IgG2a/2b isotypes. These cytophilic antibodies inhibited the ring as well as schizont stage and total parasite growth during in vitro merozoite reinvasion inhibition study. In the mixed peptide preparation, the same pattern of immune response was achieved as that of individual peptide(s) using ISCOMs delivery. Therefore, the entrapment of otherwise poorly immunogenic synthetic peptides in ISCOMs resulted in increased immunogenicity followed by strong secondary response and can be adopted for developing subunit immunogen formulation against malarial parasite.

CD4 T cell-mediated cardiac allograft rejection requires donor but not host MHC class II

Numerous studies indicate that CD4 T cells are required for acute cardiac allograft rejection. However, the precise role for CD4 T cells in this response has remained ambiguous owing to the multipotential properties of this T-cell subpopulation. In the current study, we demonstrate the capacity of CD4 T cells to serve as direct effector cells of cardiac allograft rejection. We show that CD4 T cells are both necessary and sufficient for acute graft rejection, as indicated by adoptive transfer experiments in immune-deficient SCID and rag1(-/-) recipients. We have analyzed the contribution of direct (donor MHC class II restricted) and indirect (host MHC class II restricted) antigen recognition in CD4-mediated rejection. Acute CD4 T cell-mediated rejection required MHC class II expression by the allograft, indicating the importance of direct graft recognition. In contrast, reciprocal experiments indicate that CD4 T cells can acutely reject allogeneic cardiac allografts established in rag1(-/-) hosts that were also MHC class II deficient. This latter result indicates that indirect presentation of donor antigens by host MHC class II is not required for acute CD4-mediated rejection. Taken together, these results indicate that CD4 T cells can serve as effector cells for primary acute cardiac allograft rejection, predominantly via direct donor antigen recognition and independent of indirect reactivity.

T- and B-cell nonresponsiveness to self-alphaB-crystallin in SJL mice prevents the induction of experimental allergic encephalomyelitis

The myelin-associated stress protein alphaB-crystallin triggers strong proliferative responses and IFN-gamma production by human T cells and it is considered a candidate autoantigen in multiple sclerosis. In this study we examined the capacity of alphaB-crystallin or peptides derived thereof to induce experimental autoimmune encephalomyelitis (EAE) in SJL mice. Despite extensive efforts to induce EAE using active immunization with whole alphaB-crystallin, using adoptive transfer of lymphocytes or using peptide immunizations, no clinical or histological signs of EAE could be induced. SJL mice were unable to mount proliferative T-cell responses in vitro or delayed-type hypersensitivity responses in vivo to self-alphaB-crystallin. Also, immunization with self-alphaB-crystallin did not lead to any antibody response in SJL mice while bovine alphaB-crystallin triggered clear antibody responses within 1 week. Immunizations with alphaB-crystallin-derived peptides led to the activation of IL-4-producing Th2 cells and only a few IFN-gamma-producing Th1 cells. Peptide-specific T cells showed no cross-reactivity against whole alphaB-crystallin. The inability of SJL mice to mount proinflammatory T-cell responses against self-alphaB-crystallin readily explains the lack of EAE induction by immunization with whole protein or peptides derived from it. T- and B-cell nonresponsiveness is associated with constitutive expression of full-length alphaB-crystallin in both primary and secondary lymphoid organs in SJL mice, which is seen in other mammals as well, but not in humans.

Affinity of thymic self-peptides for the TCR determines the selection of CD8(+) T lymphocytes in the thymus

Experiments with synthetic antigen peptides have suggested that a critical parameter that determines the developmental fate of an immature thymocyte is the affinity of interaction between TCR and self-peptide/MHC expressed on thymic stromal cells. To test the physiological relevance of this model for thymocyte development, we determined the affinity of the anti-HY TCR (B6.2.16) expressed on CD8(+) cells for thymic self-peptide/H-2D(b) tetramers, then examined the ability of these self-peptides to determine the outcome of B6.2.16 CD8 cell selection in the thymus. The B6.2.16 TCR bound the male HY self-antigen with high affinity. Thymic self-peptides, which are highly abundant on the surface of thymic epithelial cells, bound the B6.2.16 TCR with low affinity. The ability of self-peptides to trigger positive or negative selection of B6.2.16 CD8 cells in cultured fetal thymi was determined by the relative affinity of self-peptide/H-2D(b) for the B6.2.16 TCR. High-affinity binding of the HY self-peptide resulted in B6.2.16 TCR complex zeta chain phosphorylation and the negative selection of B6.2.16 CD8 cells. Low-affinity binding of thymic self-peptides to B6.2.16 TCR resulted in the positive selection of B6.2.16 CD8 cells. Differences between the binding affinities of self-peptides to B6.2.16 TCR accounted for the self-peptide specificity of B6.2.16 CD8 cell positive selection. We conclude that the relative affinity of TCR for thymic self-peptide/class I MHC is a critical parameter in determining fate of CD8(+) cells during thymic selection.

Induction of cytotoxic T cell responses and tumor immunity against unrelated tumors using telomerase reverse transcriptase RNA transfected dendritic cells

The polypeptide component of telomerase (TERT) is an attractive candidate for a broadly expressed tumor rejection antigen because telomerase is silent in normal tissues but is reactivated in more than 85% of cancers. Here we show that immunization against TERT induces immunity against tumors of unrelated origin. Immunization of mice with TERT RNA-transfected dendritic cells (DC) stimulated cytotoxic T lymphocytes (CTL), which lysed melanoma and thymoma tumor cells and inhibited the growth of three unrelated tumors in mice of distinct genetic backgrounds. TERT RNA-transfected human DC stimulated TERT-specific CTL in vitro that lysed human tumor cells, including Epstein Barr virus (EBV)-transformed B cells as well as autologous tumor targets from patients with renal and prostate cancer. Tumor RNA-transfected DC were used as surrogate targets in the CTL assays, obviating the difficulties in obtaining tumor cells from cancer patients. In one instance, where a tumor cell line was successfully established in culture from a patient with renal cancer, the patient's tumor cells were efficiently lysed by the CTL. Immunization with tumor RNA was generally more effective than immunization with TERT RNA, suggesting that an optimal immunization protocol may have to include TERT as well as additional tumor antigens.

Th1 and Th2 mediate acute graft-versus-host disease, each with distinct end-organ targets

STAT4 and STAT6 are transcription factors that play crucial roles in responding to IL-12 and IL-4, respectively. STAT4 gene knockout (STAT4(-/-)) mice have markedly reduced Th1 responses and enhanced Th2 responses. STAT6(-/-) mice show the inverse phenotype. We compared the ability of bone marrow transplantation (BMT) with the inclusion of spleen cells from STAT6(-/-), STAT4(-/-), and wild-type (WT) mice to produce graft-versus-host disease (GVHD) in lethally irradiated MHC-mismatched recipients. Acute GVHD mortality was more rapid when induced by cells from STAT6(-/-) mice than when induced by STAT4(-/-) cells. However, cells from STAT4(-/-) and STAT6(-/-) donors both induced delayed GVHD mortality compared with WT controls, or compared with combined STAT4(-/-) and STAT6(-/-) cells, indicating a contribution of both Th1 cells and Th2 cells to acute GVHD. Recipients of STAT6(-/-) BMT showed evidence of acute GVHD with severe diarrhea and marked weight loss. Recipients of STAT4(-/-) BMT showed signs of GVHD with only initial transient weight loss and later development of severe skin GVHD. Histopathology showed that Th2 responses were required for the induction of both hepatic and severe skin GVHD. In contrast, both Th1 cells and Th2 cells were capable of causing intestinal pathology of GVHD. Our studies demonstrate an additive role for Th1 and Th2 cells in producing acute GVHD, and suggest a cytokine-directed approach to treating end-organ manifestations of GVHD.

Definition of MHC-restricted CTL epitopes from non-variable number of tandem repeat sequence of MUC1

Mucin1 (MUC1) is expressed ubiquitously on breast cancer cells and is a potential target for the generation of cytotoxic T cells for vaccination against breast cancer. Thus far studies of the immunogenicity of MUC1 have used peptides from the variable number of tandem repeat (VNTR); mice so immunised can generate strong cellular and antibody responses to the VNTR of human MUC1. We now demonstrate that significant CTL and CTLp can be induced to other regions of MUC1. Using the whole native MUC1 molecule, the human milk fat globule membrane antigen (HMFG) linked to mannan, cytotoxic T cell precursors (CTLp) can be generated in BALB/c, C57BL/6, transgenic HLA-A*0201/K(b) and double transgenic HLA-A*0201/K(b)xhuman MUC1 (A2 K(b)MUC1) mice. By immunising with HMFG and testing selectively on (a) extracellular (non-VNTR); (b) VNTR and (c) intracellular peptides, it was shown that all three regions generated effective CTL. Further, the CTL responses to non-VNTR peptides were as strong as those generated to the VNTR. Epitope prediction algorithms were not particularly helpful to describe CTL epitopes: overlapping peptides had to be synthesised and tested to find the epitopes. Thus, for CTL generation, the whole HMFG molecule is a powerful immunogen when linked to mannan, especially as multiple peptide epitopes for presentation by many Class I molecules are contained within the one molecule. Furthermore, Class I restricted MUC1 CTL were generated in double transgenic A2 K(b)MUC1 mice by immunising with mannan-native mucin (HMFG), suggesting that tolerance to MUC1 can be overcome with mannan-HMFG.

Linkage of exogenous T-cell epitopes to the 19-kilodalton region of Plasmodium yoelii merozoite surface protein 1 (MSP1(19)) can enhance protective immunity against malaria and modulate the immunoglobulin subclass response to MSP1(19)

The degree of protection against Plasmodium yoelii asexual blood stages induced by immunization of mice with the 19-kDa region of merozoite surface protein 1 (MSP1(19)) is H-2 dependent. As a strategy to improve the protection, mouse strains with disparate H-2 haplotypes were immunized with glutathione S-transferase (GST)-MSP1(19) proteins including either a universal T-cell epitope from tetanus toxin (P2) or an I-A(k)-restricted T-cell epitope (P8) from Plasmodium falciparum Pf332. In H-2(k) mice which are poorly protected following immunization with GST-MSP1(19), GST-P2-MSP1(19) significantly improved the protection. In mice partially (H-2(k/b)) or well protected by GST-MSP1(19) (H-2(d) and H-2(b)), P2 did not further increase the protection. However, the protection of H-2(k/b) mice and to some extent H-2(k) mice was improved by immunization with GST-P8-MSP1(19). The magnitudes of immunoglobulin G1 (IgG1) and IgG2a responses in mice immunized with the GST-MSP1(19) variants correlated with low peak parasitemia, indicating a protective capacity of these IgG subclasses. In H-2(k) mice immunized with GST-P2-MSP1(19), both IgG1 and IgG2a responses were significantly enhanced. The epitope P2 appeared to have a general ability to modulate the IgG subclass response since all four mouse strains displayed elevated IgG2a and/or IgG2b levels after immunization with GST-P2-MSP1(19). In contrast, GST-P8-MSP1(19) induced a slight enhancement of IgG responses in H-2(k/b) and H-2(k) mice without any major shift in IgG subclass patterns. The ability to improve the protective immunity elicited by P. yoelii MSP1(19) may have implications for improvement of human vaccines based on P. falciparum MSP1(19).

High frequency of autoreactive myelin proteolipid protein-specific T cells in the periphery of naive mice: mechanisms of selection of the self-reactive repertoire

The autoreactive T cells that escape central tolerance and form the peripheral self-reactive repertoire determine both susceptibility to autoimmune disease and the epitope dominance of a specific autoantigen. SJL (H-2(s)) mice are highly susceptible to the induction of experimental autoimmune encephalomyelitis (EAE) with myelin proteolipid protein (PLP). The two major encephalitogenic epitopes of PLP (PLP 139-151 and PLP 178-191) bind to IA(s) with similar affinity; however, the immune response to the PLP 139-151 epitope is always dominant. The immunodominance of the PLP 139-151 epitope in SJL mice appears to be due to the presence of expanded numbers of T cells (frequency of 1/20,000 CD4(+) cells) reactive to PLP 139-151 in the peripheral repertoire of naive mice. Neither the PLP autoantigen nor infectious environmental agents appear to be responsible for this expanded repertoire, as endogenous PLP 139-151 reactivity is found in both PLP-deficient and germ-free mice. The high frequency of PLP 139-151-reactive T cells in SJL mice is partly due to lack of thymic deletion to PLP 139-151, as the DM20 isoform of PLP (which lacks residues 116-150) is more abundantly expressed in the thymus than full-length PLP. Reexpression of PLP 139-151 in the embryonic thymus results in a significant reduction of PLP 139-151-reactive precursors in naive mice. Thus, escape from central tolerance, combined with peripheral expansion by cross-reactive antigen(s), appears to be responsible for the high frequency of PLP 139-151-reactive T cells.

BALB/c mice produce blister-causing antibodies upon immunization with a recombinant human desmoglein 3

Pemphigus vulgaris (PV) is an Ab-mediated autoimmune blistering disease of mucotaneous surfaces. Over 95% of the patients with PV express DR4 or DRw6, and the disease is characterized by the presence of autoantibodies directed against desmoglein 3 (Dsg 3), a protein expressed on keratinocytes. An appropriate animal model is required to understand immunoregulation and to address the role of immunogenetic components in the production of pathogenic Abs that are characteristic of PV. Therefore, we turned to the development of a mouse model. Four strains of female mice (BALB/c, DBA/1, SJL/J, and HRS/J) were screened for their ability to produce pathogenic anti-Dsg 3 Abs. We demonstrated that only BALB/c mice immunized with a full-length Dsg 3 can produce pathogenic Abs capable of causing acantholysis of human foreskin in culture and blistering in neonatal mice. This observation suggested that either H-2d or the BALB background contains the immunogenetic makeup necessary for the production of pathogenic anti-Dsg 3 Abs. No correlation was noted between a given isotype and the pathogenic potential of autoantibodies from different strains of mice. Similarly, the pattern of reactivity of Abs with a panel of 46 synthetic peptides that span the entire Dsg 3 failed to reveal any association between binding specificity and the pathogenic potential, and suggested that pathogenic Abs might recognize conformational epitopes. Moreover, our studies showed that the epitopes recognized by pathogenic Abs are contained within the extracellular Dsg 3.

Role of inflammatory infiltrate in activation and effector function of cloned islet reactive nonobese diabetic CD8+ T cells: involvement of a nitric oxide-dependent pathway

To investigate how CD8+ T cells interact with beta cells and local inflammatory cells in islets, we have isolated CD8+ T cell clones from nonobese diabetic (NOD) spleen that recognize and destroy both islets and the NOD insulinoma cell line NIT-1. The clones destroyed NOD islets with pre-existing inflammation better than islets without signs of inflammation. Islets from NOD-scid mice were destroyed only poorly, but that could be improved by adding IL-7 to the assay. Anti-IFN-gamma Abs inhibited destruction of infiltrated islets. Single islets were effective stimulators of IFN-gamma production by cloned CD8+ T cells, which varied >50-fold depending on the degree of islet infiltration. This effect of the islet mononuclear infiltrate could be mimicked by adding spleen cells to NIT-1 cells, which augmented IFN-gamma production above the level stimulated by NIT-1 cells alone. The enhancing effect of spleen cells could be attributed to their macrophage subpopulation and was not MHC restricted, although recognition of islet Ag by cloned CD8+ T cells and subsequent islet destruction was restricted to islets expressing H-2Db molecules. An inhibitor of inducible NO synthase inhibited destruction of inflamed islets by cloned CD8+ T cells. We propose that macrophages in inflamed islets provide a form of bystander costimulation of beta cell-specific CD8+ T cells. CD8+ T cells respond to Ag and costimulation by producing IFN-gamma that activates macrophages. Activated macrophages facilitate islet destruction by CD8+ T cells through a NO synthesis-dependent pathway.

Role of Toxoplasma gondii HSP70 and Toxoplasma gondii HSP30/bag1 in antibody formation and prophylactic immunity in mice experimentally infected with Toxoplasma gondii

Production of antibodies against Toxoplasma gondii (T. gondii)-derived stress proteins, T. gondii HSP70 (T.g.HSP70) and T.g.HSP30/bagl, in C57BL/6 and BALB/c mice perorally infected with cysts of the avirulent Fukaya strain of T. gondii was analyzed. Production of anti-T.g.HSP70 IgG antibodies was transient, whereas production of anti-T.g.HSP30/bag1 IgG antibodies persisted after infection in both C57BL/6 and BALB/c mice. C57BL/6 mice, a susceptible strain, predominantly produced IgG antibodies specific for T.g.HSP70, whereas BALB/c mice, a resistant strain, predominantly produced IgG antibodies specific for T.g.HSP30/bag1, after T. gondii infection. Immunization with rT.g.HSP30/bag1 enhanced, whereas immunization with rT.g.HSP70 reduced host protective immunity against T. gondii infection with a cyst-forming avirulent strain, Fukaya, and a virulent strain, RH.

Triggering a second T cell receptor on diabetogenic T cells can prevent induction of diabetes

In this paper, we test the hypothesis that triggering of a second T cell receptor (TCR) expressed on diabetogenic T cells might initiate the onset of diabetes. A cross between two TCR-transgenic strains, the BDC2.5 strain that carries diabetogenic TCRs and the A18 strain that carries receptors specific for C5, was set up to monitor development of diabetes after activation through the C5 TCR. F1 BDC2. 5 x A18 mice developed diabetes spontaneously beyond 3-4 mo of age. Although their T cells express both TCRs constitutively, the A18 receptor is expressed at extremely low levels. In vitro activation of dual TCR T cells followed by adoptive transfer into neonatal or adult F1 mice resulted in diabetes onset and death within 10 d after transfer. In contrast, in vivo immunization of F1 mice with different forms of C5 antigen not only failed to induce diabetes but protected mice from the spontaneous onset of diabetes. We propose that antigenic stimulation of cells with low levels of TCR produces signals inadequate for full activation, resulting instead in anergy.

Spontaneous autoimmune thyroiditis in NOD.H-2h4 mice

NOD.H-2h4 mice, which express I-Ak on the NOD genetic background, spontaneously develop autoimmune thyroiditis (SAT) and anti-mouse thyroglobulin (MTg) autoantibodies. The incidence of SAT is nearly 100% in mice of both sexes 6-8 weeks after administration of 0.05% NaI in the drinking water. After reaching maximum severity, inflammation is chronic over the next 3-4 months. All mice that develop thyroid lesions also produce MTg-specific IgG1 and IgG2b autoantibodies. Thyroid lesions and anti-MTg autoantibodies did not develop in CBA/J (H-2(k)) or NOD.SWR(H-2(q)) mice after administration of NaI water. Both CD4(+)and CD8(+)T cells are involved in the initial development of SAT. Depletion of CD4(+), but not CD8(+), T cells after thyroid lesions have developed also markedly reduced SAT severity, indicating that CD4(+)T cells are required for both developing and maintaining SAT. Analysis of cytokine gene expression indicated that both Th1 and Th2 cytokines were expressed in thyroids of NOD.H-2h4 mice with SAT. Th1 and proinflammatory cytokines were maximally expressed 4-6 weeks after mice began receiving NaI water, while Th2 cytokine gene expression was greatest at 8-15 weeks, when lesions had reached maximal severity and were in the chronic phase. TGF-beta was highly expressed in NOD.H-2h4 thyroids, irrespective of whether the mice had received NaI water or had thyroid lesions.

Induction of specific T cell tolerance by Fas ligand-expressing antigen-presenting cells

Autocrine interaction of Fas and Fas ligand leads to apoptosis of activated T cells, a process that is critical for the maintenance of peripheral T cell tolerance. Paracrine interactions of Fas ligand with T cells also may play an important role in the maintenance of tolerance, as Fas ligand can create immune-privileged sites and prevent graft rejection by inducing apoptosis in T cells. We surmised that APCs that express Fas ligand might directly induce apoptosis of T cells during presentation of Ag to the T cells, thus inducing Ag-specific, systemic T cell tolerance. Here, we show that profound, specific T cell unresponsiveness to alloantigen was induced by treatment of H-2k mice with H-2b APCs that expressed Fas ligand and that profound T cell unresponsiveness specific for the H-Y Ag was induced by treatment of H-2Db/H-Y TCR transgenic female mice with H-2Db/H-Y APCs that expressed Fas ligand. The induction of this systemic T cell tolerance required the expression of Fas ligand on the APCs as well as the expression of Fas on the T cells. The tolerance was restricted to the Ag presented by the APCs. The rapid and profound clonal deletion of the Ag-specific, peripheral T cells mediated by the Fas ligand-expressing APCs contributed to the induction of tolerance. These findings demonstrate that Ag-specific T cell tolerance can be induced by APCs that express Fas ligand and suggest a novel function for APCs in the induction of T cell apoptosis. Furthermore, they indicate a novel immunointervention strategy for treatment of graft rejection and autoantigen-specific autoimmune diseases.

The murine nonclassical class I major histocompatibility complex-like CD1.1 molecule protects target cells from lymphokine-activated killer cell cytolysis

Classical class I major histocompatibility complex (MHC) molecules, as well as the nonclassical class I histocompatibility leukocyte antigen (HLA)-E molecule, can negatively regulate natural killer (NK) cell cytotoxicity through engagement of NK inhibitory receptors. We show that expression of murine (m)CD1.1, a nonpolymorphic nonclassical MHC class I-like molecule encoded outside the MHC, protects NK-sensitive RMA/S target cells from adherent lymphokine-activated killer cell (A-LAK) cytotoxicity. Passage of effector cells in recombinant interleukin (rIL)-2 enhanced protection by mCD1.1, suggesting an expansion of relevant A-LAK population(s) or modulation of A-LAK receptor expression. Murine CD1. 1 conferred protection from lysis by rIL-2-activated spleen cells of recombination activating gene (Rag)-1(-/-) mice, which lack B and T cells, demonstrating that mCD1.1 can protect RMA/S cells from lysis by NK cells. An antibody specific for mCD1.1 partially restored A-LAK lysis of RMA/S.CD1.1 transfectants, indicating that cell surface mCD1.1 can confer protection from lysis; therefore, mCD1.1 possibly acts through interaction with an NK inhibitory receptor. CD1.1 is by far the most divergent class I molecule capable of regulating NK cell activity. Finally, mCD1.1 expression rendered RMA/S cells resistant to lysis by A-LAK of multiple mouse strains. The conserved structure of mCD1.1 and pattern of mCD1.1 resistance from A-LAK lysis suggest that mCD1.1 may be a ligand for a conserved NK inhibitory receptor.