C1q-independent activation of neutrophils by immunoglobulin M-coated surfaces

Neutrophil granulocytes are known to rapidly adhere and undergo frustrated phagocytosis upon contact with immunoglobulin and/or complement protein ops onized artificial surfaces. In this study, we examined the relation between serum protein deposition and human neutrophil activation on hydrophobic gl ass and silicon model surfaces that were coated with immunoglobulin G or M (IgG/IgM), both initiators of the classical complement pathway. Protein ads orption from normal human serum (NHS) was quantified with null-ellipsometry combined with antibody techniques. The neutrophil oxygen radical productio n was registered by luminol-amplified chemiluminescence (CL) and the morpho logy, as well as changes in the content of filamentous actin (F-actin), wer e documented by fluorescence microscopy. Complement factor 3 (C3) bound to both IgG- and IgM-coated surfaces, but surprisingly C1q was found only on I gG-coated surfaces. Both immunoglobulins triggered complement dependent neu trophil activation. However, CL and F-actin accumulation were found sensiti ve to the presence of Clq in the serum only at the IgG-coated surface. We s uggest that spontaneously adsorbed IgM activates the complement system and interacts with neutrophils by C1q-independent mechanisms. (C) 2001 John Wil ey & Sons, Inc.