Kinetics of MHC gene expression and mRNA synthesis in brain endothelium

Abstract

Rat brain endothelium was examined in vitro to determine the sequence of events in MHC gene activation following IFN-gamma stimulation. The cell-triggering time, kinetics of mRNA synthesis, rate of MHC induction and rate of decay were measured by quantifying cell-surface MHC expression in the presence or absence of alpha-amanitin. Enhanced class I expression is triggered immediately after IFN-gamma stimulation, and is maximally induced by 4 hr of stimulation. New class I mRNA synthesis starts immediately and proceeds over the next 24 hr. This is followed by increased expression of class I molecules, which reaches plateau levels by 24 hr. While IFN-gamma is present, enhanced class I expression is maintained at 140-200% of that seen on resting cells. On removal of IFN-gamma, class I expression decays towards the levels seen on resting cells, with a half-life of approximately 40 hr. Class II molecules can be induced on these cells as well, but it requires the continuous presence of higher levels of IFN-gamma for more than 48 hr to trigger the cells. Induced class II molecules start to appear 2 days after pulsing and continue to increase until Day 4. If the IFN-gamma is removed from the cultures, class II expression declines rapidly towards zero, with a half-life of approximately 30 hr.