Showing papers by "Andrea J. Tenner published in 1987"

Modulation of FcR function by complement: subcomponent C1q enhances the phagocytosis of IgG-opsonized targets by human monocytes and culture-derived macrophages.

Abstract: We have investigated the interaction of C1q, a subunit of the first component of complement, with human monocytes and culture-derived macrophages. Adherence of these mononuclear phagocytes to surfaces coated with C1q induced a marked enhancement of the phagocytosis of sheep erythrocytes opsonized with IgG anti-Forssman antibody (EA-IgG). This C1q-mediated enhancement of phagocytosis was dose dependent, and was specifically blocked by pretreatment of the C1q-coated surfaces with F(ab')2 anti-C1q. The augmentation of FcR-mediated phagocytosis by C1q was determined to be a result of the interaction between the C1q and the phagocytic effector cell, and was not due to interaction between the surface-bound C1q and the EA-IgG. Neither resting nor N-formyl-methionyl-leucyl-phenylalanine-stimulated polymorphonuclear leukocytes were induced by C1q to increase FcR-mediated phagocytosis. Experiments conducted with purified fragments of C1q suggest that the C1q phagocytosis enhancement signal resides in the collagen-like tail domain of the molecule. This region is the same portion of the molecule previously shown to interact with the cell surface C1q receptor. Native type I collagen was unable to enhance FcR-mediated phagocytosis by mononuclear phagocytes. It has been demonstrated that C1q can be localized to areas of inflammation, and additionally C1q can be secreted by macrophages in culture. In view of these findings and the results of our present study, we hypothesize that C1q could provide local, direct, and non-opsonic enhancement of phagocytosis by mononuclear phagocytes in areas of infection and inflammation.

A sensitive specific hemolytic assay for proenzyme C1.

Abstract: The traditional hemolytic assay of the functional activity of C1, the first component of the classical complement pathway, was modified to permit differentiation between proenzyme (unactivated) C1 and the activated state of the enzyme (C1). A two-step assay was developed to quantitate proenzyme C1. The C1 sample to be assayed was first preincubated with C1 inhibitor, a process that specifically inhibits the enzymatic activity of C1 without affecting the subsequent activation of proenzyme C1 by EAC4, a model immune complex. Since the rate of reaction between C1 inhibitor, a serum regulatory protein, and C1 is concentration-dependent, this step is performed at high C1 and C1 inhibitor concentrations. Subsequent dilutions of the sample prevents C1 inhibitor-mediated inactivation of the C1 that is activated during the C1 hemolytic assay. Thus, in the presence of C1 inhibitor, the level of C1 hemolytic activity specifically reflects the activity of proenzyme C1, while in the absence of C1 inhibitor, the hemolytic activity reflects the total activity of C1. Both the absolute and the relative amounts of the proenzyme (unactivated) and activated C1 can thereby be quantitated in most samples. Furthermore, a partially purified C1 inhibitor reagent, easily prepared from serum, was shown to function identically to the purified C1 inhibitor, obviating the need for a multistep isolation procedure for this protein. Using this simple yet sensitive assay to investigate the efficiency of reconstitution of C1 activity from the purified components C1q, C1r, and C1s, we also find evidence for temperature- and concentration-dependent reaction steps in the formation of functional C1.