ERYTHROCYTE COMPLEMENT RECEPTORS

Primate erythrocytes express complement receptors (E-CR), which can ex trinsically bind C3b and C4b. This interaction allows primate erythroc ytes to bind complement opsonized particles and immune complexes, a ph enomenon historically referred to as immune adherence. The binding of C3b and C4b by E-CR also leads to inhibition of complement activation. The human E-CR is the complement receptor type 1, or CR1, which is co dominantly expressed as four polymorphic allotypes, ranging in size fr om 190,000 to 280,000 M(r). Non-human primate E-CR are similar to CR1 in function and antigenicity and are likely homologous to CR1 in struc ture; however, they are one third to one half the size of CR1. The phy siological role of E-CR, determined from studies in monkeys and humans , is to allow erythrocytes to perform as inert shuttles for circulatin g immune complexes (IC), safely directing IC to the organs of the mono cyte phagocytic system, thus preventing indiscriminate IC deposition i n vulnerable tissue. In IC-mediated diseases, such as systemic lupus e rythematosus (SLE), detectable erythrocyte CR1 levels are reduced, an abnormality that in part is acquired during disease activity. The loss of erythrocyte CR1 may be an important pathogenic factor in the devel opment and severity of SLE.