Membrane-associated complement factor H on lymphoblastoid cell lines Raji expresses a co-factor activity for the factor I-mediated cleavage of C3b.

Evidence of factor H was found on the surface of Raji cells derived from two different lines; a 150,000 MW species identical to 150,000 MW plasma factor H was detected. Rosette experiments performed at physiological ionic strength using EAC3b or EC3b were negative. In contrast, Raji cells expressed a co-factor activity in the factor I-mediated cleavage of fluid-phase C3b. This activity was cell number dependent and was inhibited by anti-factor H but not by anti-CR1. Raji cells did not secrete factor H in the extracellular medium.