EXPRESSION AND CHARACTERIZATION OF RECOMBINANT SOLUBLE PEPTIDE - I-A COMPLEXES ASSOCIATED WITH MURINE EXPERIMENTAL AUTOIMMUNE-DISEASES

Structural and functional studies of murine MHC class II I-A molecules have been limited by the low yield and instability of soluble, recomb inant heterodimers. In the murine autoimmune diseases experimental aut oimmune encephalomyelitis and collagen-induced arthritis, MHC class II molecules I-A(u) and I-A(q) present peptides derived from myelin basi c protein and type II collagen, respectively, to autoreactive T cells. To date, systems for the expression of these two I-A molecules in sol uble form for use in structure-function relationship studies have not been reported. In the present study, we have expressed functional I-A( u) and I-A(q) molecules using a baculovirus insect cell system, The ch ain pairing and stability of the molecules were increased by covalentl y linking the antigenic peptides to beta-chains and adding carboxyl-te rminal leucine zippers. Peptide:I-Ag complex quantitatively formed an SDS-stable dimer, whereas peptide:I-A(u) formed undetectable amounts. However, the two complexes did not show any significant difference in their response to thermal denaturation as assessed by circular dichroi sm analyses, The autoantigen peptide:I-A complexes were highly active in stimulating cognate T cells to secrete IL-2 and inducing Ag-specifi c apoptosis of the T cells. Interestingly, the T cells were stimulated by these soluble molecules in the apparent absence of experimentally induced cross-linking of TCRs, indicating that they may have therapeut ic potential in autoimmune disease models.