Antigen presentation in brain: MHC induction on brain endothelium and astrocytes compared

Primary cultures of rat brain endothelium and astrocytes were cultured in vitro, stimulated with interferon-gamma (IFN gamma), and the levels of MHC expression were then measured by an enzyme immunoassay (EIA). Class I expression is enhanced on brain endothelium by Day 1 following stimulation, and attains a plateau level of expression. Class II is normally absent, but starts to appear at Day 2, and continues to increase until Day 5. Class II rat I-A homologue is induced much more strongly than I-E, and the dose-response curves show that I-A expression is dependent on interferon dose within the range 2-500 units/ml, whereas class I enhancement is uniform over this range. The endothelium was compared with astrocytes, in regard to MHC induction. The surface density of class I and class II molecules was lower on the astrocytes in all conditions, and both class I enhancement and class II induction were in some cases slower to appear than on endothelium treated similarly. We also describe a pre-astrocytic cell line, C9, which shows strong I-E expression when stimulated with IFN gamma, but is apparently unable to express I-A. The implications of these findings for the development of immune reactions in the brain are discussed.