Assays for membrane complement receptors

Leukocytes express several types of receptors for activated products of the complement (C) system. This unit describes assays for a subset of these receptors: those specific for fixed fragments of C3 (CR1, CR2, CR3, and CR4). Although the assays have been designed for tests of human C receptors, they can often be carried out with rodent (e.g., mouse, rat, or guinea pig) cells by substitution of rodent-specific reagents. Two basic protocols are presented for rosette assay of CR1, CR2, CR3, and CR4 on adherent and nonadherent cells. Isolated leukocytes may be tested for rosette formation in suspension or adherent to a surface. Nonadherent cells such as lymphocytes, NK cells, or cells from an undifferentiated leukocyte cell line must be tested in suspension. The unit also contains three support protocols for formation and quantitation of sheep erythrocyte-C3 complexes for use in the two basic protocols.