Treatment-resistant Lyme arthritis is associated with immune reactivity to outer surface protein A (OspA) of Borrelia burgdorferi, the agent of Lyme disease, and the major histocompatibility complex class II allele DRB1*0401. The immunodominant epitope of OspA for T helper cells was identified. A homology search revealed a peptide from human leukocyte function-associated antigen-1 (hLFA-1) as a candidate autoantigen. Individuals with treatment-resistant Lyme arthritis, but not other forms of arthritis, generated responses to OspA, hLFA-1, and their highly related peptide epitopes. Identification of the initiating bacterial antigen and a cross-reactive autoantigen may provide a model for development of autoimmune disease.

SummaryTo investigate the development of HLA-DR-associated autoimmune diseases, we generated transgenic (Tg) mice with HLA-DRA-IEcx and HLA-DRBI*0401-IE[3 chimeric genes. The transgene-encoded proteins consisted of antigen-binding domains from HLA-DRA and HLA-DRBI*0401 molecules and the remaining domains from the IEd-ot and IEd-[3 chains. The chimeric molecules showed the same antigen-binding specificity as HLA-DRBI*0401 molecules, and were functional in presenting antigens to T cells. The Tg mice were backcrossed to MHC class II-deficient (IAl3-,IEoe-) mice to eliminate any effect of endogenous MHC class II genes on the development of autoimmune diseases. As expected, IA~x[3 or IEot[3 molecules were not expressed in Tg mice. Moreover, cell-surface expression of endogenous IE[3 associated with HLA-DRA-IEci was not detectable in several Tg mouse lines by flow cytometric analysis. The HLA-DRA-IEo~/HLA-DRBI*0401-IE[3 molecules rescued the development ofCD4 + T cells in MHC class II-deficient mice, but T cells expressing VI35, V1311, and VI312 were specifically deleted.Tg mice were immunized with peptides, myelin basic protein (MBP) 87-106 and proteolipid protein (PLP) [175][176][177][178][179][180][181][182][183][184][185][186][187][188][189][190][191][192], that are considered to be immunodominant epitopes in HLA-DR4 individuals. PLP175-192 provoked a strong proliferative response of lymph node T cells from Tg mice, and caused inflammatory lesions in white matter of the CNS and symptoms of experimental allergic encephalomyelitis (EAE). Immunization with MBP87-106 elicited a very weak proliferative T cell response and caused mild EAE. Non-Tg mice immunized with either PLP175-192 or MBP87-106 did not develop EAE. These results demonstrated that a human MHC class II binding site alone can confer susceptibility to an experimentally induced murine autoimmune disease.

We have examined trafficking of major histocompatibility complex (MHC) class II molecules in human B cells exposed to concanamycin B, a highly specific inhibitor of the vacuolar H(+)‐ATPases required for acidification of the vacuolar system and for early to late endosomal transport. Neutralization of vacuolar compartments prevents breakdown of the invariant chain (Ii) and blocks conversion of MHC class II molecules to peptide‐loaded, SDS‐stable alpha beta dimers. Ii remains associated with alpha beta and this complex accumulates internally, as ascertained biochemically and by morphological methods. In concanamycin B‐treated cells, a slow increase (> 20‐fold) in surface expression of Ii, mostly complexed with alpha beta, is detected. This surface‐disposed fraction of alpha beta Ii is nevertheless a minor population that reaches the cell surface directly, or is routed via early endosomes as intermediary stations. In inhibitor‐treated cells, the bulk of newly synthesized alpha beta Ii is no longer accessible to fluid phase endocytic markers. It is concluded that the majority of alpha beta Ii is targeted directly from the trans‐Golgi network to the compartment for peptide loading, bypassing the cell surface and early endosomes en route to the endocytic pathway.

We have analyzed the structural diversity of the murine y6 T-cell receptor (TCR) heterodimer expressed on CD4-CD8-thymocyte populations and on TCR yOexpressing hybridomas derived from thymocytes of fetal, newborn, and adult mice. We found that CD4-CD8-thymocytes derived from mice of different pre-and postnatal age preferentially express a yv TCR encoded by different subsets of y and 8 gene segments. This age-dependent differential expression of Y8 TCR on thymocytes seems to be accomplished in part by a specific control of rearranged 'y genes operating at the level of transcription and/or RNA stability. We discuss the implications of these findings with respect to the recognition roles ofthe y6 TCR.The specific antigen recognition structure (T-cell receptor; TCR) of major histocompatibility complex (MHC)-restricted T-cells is composed of two polymorphic glycosylated polypeptide chains, TCR a and TCR P, noncovalently associated with an invariant protein complex, termed CD3. More recently, discovery of a third rearranging gene, y, which is expressed specifically in T cells (1, 2), led to the identification of another CD3-associated heterodimer containing polymorphic TCR y and TCR 8 chains on subsets of immature thymocytes (3-6), peripheral T cells (7-9), dendritic epidermal cells (DEC) (10, 11), and gut intraepithelial lymphocytes (IEL) (12,13). The role of the y8 receptor is yet to be established. Analysis of rearrangement and expression of TCR y and 8 genes during fetal ontogeny have suggested a possible coordinate control in the rearrangements and expression of these loci (14-16). In the present study, we have analyzed the structure and diversity of y and 8 polypeptide chains on CD4-CD8-[hereafter referred to as double negative (DN)] thymocytes and on y8-expressing T-cell hybridomas derived from fetal and adult thymocytes.Our observations strongly suggest that different sets of y-chain variable region (V.) and 8-chain variable region (Vs) genes are expressed on fetal, newborn, and adult thymocytes and that some V8 species preferentially pair with specific VY products to form a y5 TCR. In addition, we suggest the possibility of V,-dependent control of y gene transcription. MATERIALS AND METHODSAnimals. C57BL/6 (B6) and BALB/c mice were purchased from The Jackson Laboratory.Preparation of y6 T-Cell Hybridomas. DN thymocytes were obtained after treatment of cells with anti-L3T4 monoclonal antibody (mAb) (RL172.4) and anti-Lyt-2 mAb (3.155.D14) plus rabbit complement (Cederlane Laboratories, Hornby, ON, Canada) as described (8) Northern Blot Analysis. Ten micrograms of formaldehydetreated total RNA was subjected to electrophoresis in a 1% agarose gel containing formaldehyde, transferred to nylon membranes, and hybridized to random-primed probes in the presence of 50%o formamide/1% SDS/1 M NaCI/10% dextran sulfate at 42°C. Filters were then washed in 2x SSC/1% SDS at 60°for 1 hr. RESULTS Distinct y5 TCR on Embryonic and Adult ThymocytePopulations. It has been reported that both the DNA rearrangement and RN...