PREVENTION OF SYSTEMIC LUPUS-ERYTHEMATOSUS IN AUTOIMMUNE BXSB MICE BYA TRANSGENE ENCODING I-E-ALPHA-CHAIN

Males from the BXSB murine strain (H-2b) spontaneously develop an auto immune syndrome with features of systemic lupus erythematosus (SLE), w hich results in part from the action of a mutant gene (Yaa) located on the Y chromosome. Like other H-2b mice, the BXSB strain does not expr ess the class II major histocompatibility complex antigen, I-E. Here w e report that the expression of I-E (Ealpha(d)Ebeta(b)) in BXSB males bearing an Ealpha(d) transgene prevents hypergammaglobulinemia, autoan tibody production, and subsequent autoimmune glomerulonephritis. These transgenic mice bear on the majority of their B cells not only I-E mo lecules, but also an I-E alpha chain-derived peptide presented by a hi gher number of I-A(b) molecules, as recognized by the Y-Ae monoclonal antibody. The I-E+ B cells appear less activated in vivo than the I-E- B cells, a minor population. This limited activation of the I-E+ B ce lls does not reflect a functional deficiency of this cell population, since it can be stimulated to IgM production in vitro by lipopolysacch arides at an even higher level than the I-E- B cell population. The de velopment of the autoimmune syndrome in the transgenic and nontransgen ic bone marrow chimeric mice argues against the possibility that the i nduction of regulatory T cells or clonal deletion of potential autorea ctive T cells as a result of I-E expression is a mechanism of the prot ection conferred by the Ealpha(d) transgene. We propose a novel mechan ism by which the Ealpha(d) transgene protects BXSB mice against SLE: o verexpression of I-E alpha chains results in the generation of excessi ve amounts of a peptide displaying a high affinity to the I-A(b) molec ule, thereby competing with pathogenic autoantigen-derived peptides fo r presentation by B lymphocytes and preventing their excessive stimula tion.