Calcium signalling initiated by CR1 (CD35) crosslinking is mediated by phagocyte Fc gamma receptors in cis.

We have examined the role of complement receptor type 1 (CR1; CD35) in generating intracellular signals in phagocytic cells, particularly human neutrophils. We find that crosslinking of CR1 alone fails to result in an increase in intracellular ionized calcium [Ca2+]i. However, IgG bound to CR1 is able to interact with Fc gamma receptors to stimulate increases in [Ca2+]i. By examining signals generated in mixed populations of cells, we determined that calcium increases are observed only when CR1 and Fc gamma receptors are engaged on the same cell. Functional interactions between complement receptors and receptors for immunoglobulin G may promote clearance of pathogenic bacteria and fungi that bind limited quantities of complement and IgG.