Antigen presentation in brain: brain endothelial cells are poor stimulators of T-cell proliferation

The capacity of rat brain capillary endothelium to present antigen to primed peripheral lymph node cells or to ovalbumin-specific T-cell lines was examined in vitro. Brain endothelium can present antigen, but it is generally ineffective at stimulating T-cell division. Division is only seen when indomethacin is included in the cultures to suppress eicosanoid production. Even under these conditions an endothelial monolayer is only 1/40 as effective as a thymocyte monolayer in stimulating division. The failure to act as an effective antigen presenting tissue is not due to lack of IL-1 production, nor is it related to the extended time required to induce MHC class II molecules on these cells. In the presence of high levels of antigen-specific T cells, the endothelium appears to be subject to cytotoxic damage, so that T-cell stimulation is lowest with higher numbers of T cells--the opposite of that seen with conventional antigen-presenting cells. These findings support the view that brain endothelial cells are not important in stimulating T-cell division during the development of immune reactions in brain, although these cells may be recognizable by class II-restricted cytotoxic cells.