Experimental allergic encephalomyelitis: clinical disease and enhanced cellular transfer in the absence of lymphocyte proliferative responses against syngeneic MBP

Contrasting immunopathogenic properties of highly homologous peptides from rat and human thyroglobulin

The current lack of amino acid sequence data for mouse thyroglobulin (Tg) necessitates mapping of pathogenic T-cell epitopes on heterologous Tg in mouse experimental autoimmune thyroiditis (EAT). A prevailing assumption has been that epitopes sharing a high degree of amino acid homology among heterologous Tg are likely to exhibit the same immunopathogenic properties in the same host. In this report, we have examined this concept while working with the 18-mer rat(r)Tg(2695-13) peptide that was previously shown to elicit 'A'-restricted T cells and EAT in SJL mice. A major immunopathogenic T-cell epitope was localized within the 12-mer rTg(2695-06). It was found that the human 12-mer homologue that carries two Ser substitutions at Glu2703 and Thr2704 exhibited contrasting properties: it failed to activate Th1 cells in lymphokine and proliferation assays; it did not cross-react with rTg(2695-06) at the T-cell level; and it induced only focal thyroiditis following adoptive transfer of specific lymph node cells. These data highlight the caveat involved in extrapolating results of pathogenic T-cell epitope mapping across heterologous Tgs, even when such epitopes share a high degree of amino acid homology.

Mapping of thyroglobulin epitopes: presentation of a 9mer pathogenic peptide by different mouse MHC class II isotypes

We have previously reported that the 17mer thyroglobulin (Tg) peptide TgP1 (a.a. 2495-2511) induces experimental autoimmune thyroiditis (EAT) in H-2k mice, a process requiring expression of Ek genes, and in H-2s mice that lack functional E molecules. To test whether this apparent discrepancy was due to recognition of distinct TgP1 determinants in each strain, we mapped in this study minimal T-cell epitopes within TgP1 and examined their pathogenicity in C3H (H-2k) or SJL (H-2s) mice. Truncation analysis using TgP1-specific, CD4+ hybridomas from C3H mice identified two overlapping determinants, (2496-2504) and (2499-2507), that were restricted by the Ek and Ak molecules, respectively. Subsequent challenge of C3H and SJL mice with these 9mer peptides revealed that the Ek-restricted (2496-2504) determinant elicited EAT and specific proliferative LNC responses in both strains, suggesting recognition in the context of As, since this is the only class II molecule expressed in SJL mice. This was further confirmed by blocking of the proliferative LNC response by an As-specific monoclonal antibody. In contrast, the Ak-restricted (2499-2507) determinant induced weak EAT and no proliferative LNC responses in either strain. These data 1) delineate the 9mer (2496-2504) peptide as a minimal Tg T-cell epitope with direct pathogenic potential in mice and 2) highlight the use of nonisotypic MHC class II molecules for the presentation of this peptide in mice of different H-2 haplotypes. T-cell level. Despite its nondominant nature, TgP1 induces experimental autoimmune thyroiditis (EAT) with a genetic pattern similar to that obtained with intact Tg, and elicits strong specific T-cell responses as well as IgG responses that cross-react with Tgs from different species (Chronopoulou et al. 1992). For these reasons, TgP1-mediated EAT provides an excellent model for studying the immunoregulatory mechanisms leading to mononuclear infiltration of the thyroid and hypothyroidism--the main symptoms of Hashimoto's disease in humans (Weetman 1992). Earlier work (Chronopoulou et al. 1993) has demonstrated that Ek expression is a necessary but not sufficient requirement for EAT induction with TgP1 and suggested involvement of the Kk and/or Ak loci in the disease process. In apparent contrast to these findings, however, SJL mice that lack H-2E molecules were found to be EAT-susceptible after TgP1 challenge (Chronopoulou et al. 1992).(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of the uveitogenic determinant in repeat structure of retinal interphotoreceptor retinoid-binding protein (IRBP)

IRBP is a glycolipoprotein with a four-fold partially homologous repeat structure approximately 300 residues in length, and is one of the retinal antigens capable of inducing experimental autoimmune uveoretinitis (EAU) in susceptible animals by their active immunization. The most immunopathogenic peptide of bovine IRBP for EAU in Lewis rats is reported to be the sequence 1169-1191 (PTARSVGAADGSSWEGVGVVPDV) with two immunogenic motifs common to T cell epitopes (underlined). The uveitogenic site of peptide 1169-1191 was localized at the carboxyl terminus (peptide 1182-1191) and not at the amino acid terminus (peptide 1169-1182). Repeat peptides of sequence 1179-1191 containing the four homologous residues (1182W, 1186G, 1187V and 1189P), that is the peptides 271-283, 579-591 and 880-892, all elicited EAU. Peptide 579-591 could not stimulate proliferation of lymphocytes from rats immunized with IRBP, but had the capacity to adoptively transfer EAU. The role of the homologous residues was examined using analogues of the uveitogenic peptide 1182-1194, in which each homologous residue was substituted by glycine (G) or leucine (L) (1182W-->G, 1186G-->L, 1187V-->G, and 1189P-->G). One analogue (1186G-->L) strongly diminished the ability to induce EAU, while the other three analogues completely abolished the ability, indicating that these homologous residues were essential for the induction of EAU. In addition, the uveitogenic peptides tested in this study were found not to contain the major epitope for antibody production.

Analysis of type II collagen-reactive T cells in the mouse. I. Different regulation of autoreactive vs. non-autoreactive anti-type II collagen T cells in the DBA/1 mouse

The T cell reactivity against type II collagen (CII) was analyzed in the collagen-induced arthritis-susceptible mouse strain DBA/1. It was shown that the proliferative response in lymph node cells from rat CII-immunized mice was mainly directed against a foreign determinant present on all heterologous CII tested but not on autologous CII. A T cell line with this reactivity reacted with high sensitivity with CII and the determinant was mapped to the CB11 fragment of CII. A weak autoreactive response could be detected in the primary cultures using high concentrations of mouse CII and this reactivity remained after several stimulations with high concentrations of rat CII but not with low concentrations of rat CII. A similar response against mouse CII but with only limited cross-reactivity to rat CII was seen when culturing the cells with mouse CII as antigen. The optimal concentration for the autoreactive response was always more than 100-fold higher than for the response of the T cells specific for heterologous CII. An anti-CII T cell response could also be detected in spleen cells from unimmunized mice and the strongest response was obtained using autologous CII. These results suggest that T cells recognizing self CII are normally activated in the DBA/1 mouse and possibly as a consequence exhibit a clonal anergy pattern with a weak proliferative response only at high concentrations of CII.

Uveitopathogenic sites in bovine S-antigen

Experimental autoimmune uveitis (EAU) was observed in Hartley guinea pigs following immunization with high doses (200 micrograms) of four synthetic peptides designated peptide 3, K, N and M which correspond to amino acid positions 221-240, 241-260, 281-302, and 303 to 320 respectively in bovine S-antigen. Histopathologically, a moderate inflammatory response involving the uveal tract and retina was observed using peptide N and peptide M as immunogens, whereas peptide 3 and peptide K caused only a mild inflammatory response with very few inflammatory cells in the retina. In contrast, animals with EAU showed an associated pinealitis (EAP) characterized by an extensive lymphocytic infiltration of the central and subcapsular areas of the pineal gland. Lymph node cells of guinea pigs immunized with peptide 3, peptide K, peptide N or peptide M showed strong in vitro proliferative responses against the respective immunizing peptide as measured by [3H] thymidine uptake. The results suggest that under appropriate experimental conditions S-antigen may contain multiple pathogenic sites. The relevance of these studies in the pathogenesis of EAU is discussed.

Differential effects of cyclosporins A and G on functional activation of a T-helper-lymphocyte line mediating experimental autoimmune uveoretinitis

The effect and relative efficiency of cyclosporin A (CsA) and cyclosporin G (CsG) on suppressing the activation of primed autoimmune rat T-helper lymphocytes were assayed. The autoimmune T-helper cells (ThS) are a long-term line specific to the retinal soluble antigen (SAg) and can adoptively transfer experimental autoimmune uveoretinitis (EAU), after in vitro reactivation with antigen or mitogen, to naive syngeneic hosts. Antigen-driven production of interleukin-2 (IL-2) and antigen-driven proliferation were inhibited in a dose-dependent manner and to a similar extent at each of the respective cyclosporin concentrations. CsA was 8-10 times more potent than CsG, with ID50-CsA occurring at 0.5 to 2 ng/ml, and ID50-CsG at 5 to 20 ng/ml, depending on the experiment and the cyclosporin batch. Addition of exogenous lymphokines in the form of rat spleen concanavalin A (Con A)-conditioned medium (SCM) or recombinant IL-2 (but not recombinant IL-1) was able to reverse only about half of the inhibition, as measured along the linear part of the dose-response curve. Inhibition of IL-2 production was lost if a maximally inhibitory dose of cyclosporin was added to the cultures later than 8 hr after antigen stimulation, while proliferation was still suppressed to 50% by cyclosporin added as late as 12 hr and could not be restored by addition of SCM. Both cyclosporins at concentrations that blocked proliferation and IL-2 production significantly suppressed the generation of high-affinity and low-affinity IL-2 receptors by ThS in response to antigen (as assayed by direct binding of 125I-IL-2). These results suggest that CsA and CsG inhibit antigen-induced expansion of ThS by interfering with more than one activation step. In contrast, the in vitro activation of the uveitogenic potential of ThS cells, incubated with antigen in the presence of CsA or CsG and adoptively transferred into untreated recipients, was not affected by the cyclosporins. Thus, triggering of the pathogenic potential of primed autoimmune T-helper lymphocytes can take place in the presence of cyclosporin and in the absence of cellular proliferation.

Uveitis induced in primates by IRBP: humoral and cellular immune responses

In a previous publication, we have reported that immunization with bovine interphotoreceptor retinoid-binding protein (IRBP) produces severe uveitis in monkeys. The present study further examined the uveitogenicity of IRBP and analysed the immune responses in the immunized monkeys. Uveitis developed in monkeys immunized with bovine IRBP at doses as low as 10 micrograms Kg-1 body wt. In contrast, no disease was detected in monkeys immunized with monkey IRBP at the total dose of 100 micrograms Kg-1. Serum antibodies were measured in the immunized monkeys by the enzyme-linked immunosorbent assay, while cellular immunity was determined by skin hypersensitivity and the lymphocyte mitotic reaction in culture. No humoral or cellular immune responses were detected in monkeys immunized with monkey IRBP. Monkeys immunized with bovine IRBP produced antibodies which cross-reacted well with monkey IRBP. On the other hand, these monkeys did not react with monkey IRBP by skin hypersensitivity and their lymphocytes responded in culture to this protein only when tested by a highly sensitive procedure. In contrast, significant responses of the same cells to bovine IRBP were obtained at all tested conditions. These data are interpreted to suggest that the pathogenic cellular immune responses in vivo detect cross-reactivity with this autologous ocular antigen more efficiently than most conventional laboratory tests.

Experimental allergic encephalomyelitis in the Lewis rat. A model of predictable relapse by cyclophosphamide

Relapse of experimental allergic encephalomyelitis (EAE) was achieved in Lewis rats by cyclophosphamide (CY). All rats, immunized with an emulsion of guinea pig spinal cord homogenate in complete Freund's adjuvant and treated with 100 mg/kg of CY 21 days postimmunization (pi), developed moderate to severe paralysis 9-14 days following CY injection. A second relapse was observed in 4 of 11 rats reinjected with CY 49 days pi. Histologically, focal mononuclear cell infiltration with or without demyelination of the white matter of the central nervous system was observed. Cyclophosphamide administration caused transient leukopenia and T-cell defect, the resolution of which coincided with relapse of clinical EAE. Lymphocyte proliferative responses to myelin basic protein (BP) and concanavalin A (Con A) and antibody titers to BP were preserved in CY-treated rats. Adoptive transfer of EAE to naive recipients with Con A-activated spleen cells from donors with CY-induced relapse was unsuccessful.