Presence of serum modulates expression of complement receptor type 1 (CR1) on human granulocytes after quartz exposure.

We have investigated the interaction between granulocytes and quartz with respect to the expression of complement receptor type 1 (CR1) and the presence of normal human serum (NHS). Quartz down-regulates selectively CR1 on activated granulocytes. This down-regulation is abolished in the presence of both NHS and heat-inactivated NHS (NHS56) but not human albumin. When quartz was preincubated with NHS (quartz-NHS) before exposure to activated granulocytes, a down-regulating effect was observed in contrast to preincubation with NHS56, which did not induce a down-regulation. Preincubation with cytochalasin B reduced the down-regulation of quartz-NHS, indicating a cytoskeleton-dependent internalization of the receptor. The serine protease inhibitor PMSF partly reduced this down-regulation. Our results indicate that the presence of NHS in the alveolar space influences the interaction between quartz and recruited granulocytes with respect to CR1 expression. Since CR1 is an important opsonin receptor and soluble CR1 can modulate the inflammatory response, this may be of importance in the inflammation and fibrosing process induced by quartz in the alveolar space and lung interstitium.