Identification of human complement factor H as a chemotactic protein for monocytes.

We used chromatographic separation to purify to homogeneity a monomeric monocyte chemotactic protein of 150 kDa contained in mesothelioma pleural effusions. It was identified by N-terminal amino acid sequencing and immunoblotting as complement factor H, an inhibitor of the alternative complement pathway. Specific antibodies against factor H inhibited the monocyte chemotactic activity of the purified protein, which was most active at 10 nM. Factor H is a restrictive factor of alternative complement pathway activation. The new chemotactic function assigned to factor H in recruiting monocytes to the mesothelioma site might contribute to malignant cell phagocytosis via the iC3b/complement receptor type 3 pathway. These functions link the humoral and cellular immune systems.