Factor H-related protein-5: a novel component of human glomerular immune deposits

Factor H-related protein-5 (FHR-5) is a newly described human plasma protein with structural similarities to human factor H and the four other recently described factor H-related proteins. Unlike the other factor H-related proteins, FHR-5 was initially identified at the protein, rather than complementary DNA, level in studies of glomerular immune deposit composition. To determine the incidence and pattern of detection of FHR-5 in human renal biopsy specimens, a prospective study of 100 consecutive biopsies was performed using anti-FHR-5 monoclonal antibody and indirect immunofluorescence. The pattern of FHR-5 deposition is very similar to that of other complement components, C3 and SC5b-9. It is detected in all complement-containing glomerular immune deposits and has a pattern of extraglomerular deposition similar to that of other complement components. This study shows FHR-5 to be strongly associated with glomerular complement deposition and suggests a role in complement activation or regulation. It may be an important mediator of glomerular disease.