DIFFERENTIAL EXPRESSION OF BOVINE MHC CLASS-II ANTIGENS IDENTIFIED BYMONOCLONAL-ANTIBODIES

Four monoclonal antibodies (mAbs), UC-A4, UC-D3, UC-H9, and IL-A21, sp ecific for bovine major histocompatibility complex class II proteins a re described. Sequential immunoprecipitation experiments using biotin- labeled peripheral blood mononuclear cells suggested, but did not conc lusively establish, that each of these antibodies recognized a differe nt epitope. The epitope identified by IL-A21 appeared to be common to all of the class II proteins precipitated by the four mAbs, and UC-D3 and UC-H9 each appeared to react with distinct epitopes on separate su bsets of these class II proteins. Monoclonal antibody UC-A4 appeared t o identify an epitope on a subset of the class II molecules identified by UC-H9. Differences found in the expression by lymphoid cells of cl ass II proteins identified by the four mAbs were indicative of each mA b recognizing a different epitope. UC-H9 and IL-A21 class II proteins were detected on all surface immunoglobulin (S'Ig) positive cells in p eripheral blood, but UC-A4 and UC-D3 class II proteins were not. Expre ssion of UC-A4 class II proteins, detected at low density on a strikin gly reduced number of S'Ig+ cells from the blood of some bovine leukos is virus-infected cattle, could be increased by culturing these B cell s with lipopolysaccharide. All peripheral blood monocytes expressed UC -H9 and IL-A21 class II proteins, but only a proportion of monocytes e xpressed detectable UC-A4 and UC-D3 class II proteins. Almost all mito gen-stimulated BoCD4+ and BoCD8+ T cells expressed UC-H9 and IL-A21 cl ass II proteins, whereas fewer stimulated T cells of both subsets expr essed UC-A4 and UC-D3 class II proteins. All gamma/delta receptor (gam ma/delta R) T cells expressed UC-D3, UC-H9, and IL-A21 class II protei ns, but no cells (of gamma/delta R+ or CD4+/CD2+ phenotype) from gamma /delta R+ T cell-enriched cultures expressed UC-A4 class II proteins.