Expression and function of lymphocyte function associated antigen-3 (LFA-3) at the blood-brain barrier

Lymphocyte function associated antigen-3 (LFA-3) is a cell surface glycopro tein involved in antigen independent T-cell activation and proliferation. T he expression and function of LFA-3 at the blood-brain barrier were studied in an in vit ro model consisting of primary cultures of human brain microv essel endothelial cells (HBMEC). Surface expression of LFA-3 was detected b y immunogold silver staining and the presence of RNA by reverse transcripta se-polymerase chain reaction (RT-PCR). Unstimulated HBMEC in primary cultur e constitutively express LFA-3 on their surface. Expression is only margina lly upregulated following stimulation with tumor necrosis factor-alpha (TNF -alpha) or interferon-gamma (IFN-gamma). Similarly, LFA-3 RNA is present co nstitutively in unstimulated HBMEC with minimal increase after co-incubatio n with TNF-alpha and IFN-gamma. The function of LFA-3 as a costimulatory mo lecule on HBMEC was investigated by incubating purified CD4+ T-lymphocytes with resting or IFN-gamma treated HBMEC monolayers. Proliferation of alpha- CD3 activated CD4+ T-cells was significantly increased upon incubation with resting or activated endothelial cells. Monoclonal antibodies to LFA-3 con sistently blocked the proliferative response by 64-76%. The ability of the cerebral endothelium to express LFA-3 and provide secondary signals for T-c ell proliferation suggests that cerebral EC may be important in the initiat ion of inflammatory responses in the human central nervous system.