Brain microvascular smooth muscle expresses class II antigens

Mouse (BALB/c) splenic lymphocytes co-cultured in vitro with syngeneic brain-derived microvascular smooth muscle (SM) proliferate and become activated. After subsequent transfer of the activated lymphocytes to a syngeneic host, a vasculitis develops in the host. Investigation of the possible antigen-presenting properties of the cultured SM has resulted in the demonstration of class II (Ia) antigens on the SM. Fluorescence-activated cell sorter analysis has shown that an average of 31% of unstimulated SM cells in culture were positive when stained with an anti-IE of the appropriate haplotype (H2d), and an average of 20% were positive with an anti-IA of the H2d haplotype. Controls consisting of irrelevant antibodies of the same isotype, as well as an anti-IA of the H2s haplotype, were negative. In contrast, BALB/c-derived brain microvascular endothelial cells showed considerably less class II antigen expression (7% for both IA and IE).