PubMed · 6357874
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J H Newman. 1983. Circulating immune complexes: a review.. https://pubmed.ncbi.nlm.nih.gov/6357874/
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We compared the phagocytosis of immune complexes (IC) and iC3b-opsonized derivatives (iC3b-IC) by human neutrophils. The phagocytosis of iC3b-IC via Fc gamma R and CR3 was much greater than that of IC via Fc gamma R alone. Adding ethanol to the cells decreased iC3b-IC phagocytosis to that of IC, which was not affected by these reagents, suggesting that the enhanced phagocytosis is attributable to CR3-mediated phospholipase D activation. The IC phagocytosis was inhibited more effectively by anti-Fc gamma IIIB, whereas the iC3b-IC phagocytosis was partly inhibited only by anti-Fc gamma RII. The main Fc gamma R might differ in IC and iC3b-IC phagocytosis.
To examine the role of complement components as regulators of the expression of endothelial adhesive molecules in response to immune complexes (ICs), we determined whether ICs stimulate both endothelial adhesiveness for leukocytes and expression of E-selectin and intercellular and vascular cell adhesion molecules 1 (ICAM-1 and VCAM-1). We found that ICs [bovine serum albumin (BSA)-anti-BSA] stimulated endothelial cell adhesiveness for added leukocytes in the presence of complement-sufficient normal human serum (NHS) but not in the presence of heat-inactivated serum (HIS) or in tissue culture medium alone. Depletion of complement component C3 or C8 from serum did not prevent enhanced endothelial adhesiveness stimulated by ICs. In contrast, depletion of complement component C1q markedly inhibited IC-stimulated endothelial adhesiveness for leukocytes. When the heat-labile complement component C1q was added to HIS, the capacity of ICs to stimulate endothelial adhesiveness for leukocytes was completely restored. Further evidence for the possible role of C1q in mediating the effect of ICs on endothelial cells was the discovery of the presence of the 100- to 126-kDa C1q-binding protein on the surface of endothelial cells (by cytofluorography) and of message for the 33-kDa C1q receptor in resting endothelial cells (by reverse transcription-PCR). Inhibition of protein synthesis by cycloheximide blocked endothelial adhesiveness for leukocytes stimulated by either interleukin 1 or ICs in the presence of NHS. After stimulation with ICs in the presence of NHS, endothelial cells expressed increased numbers of adhesion molecules (E-selectin, ICAM-1, and VCAM-1). Endothelial expression of adhesion molecules mediated, at least in part, endothelial adhesiveness for leukocytes, since leukocyte adhesion was blocked by monoclonal antibodies directed against E-selectin. These studies show that ICs stimulate endothelial cells to express adhesive proteins for leukocytes in the presence of a heat-labile serum factor. That factor appears to be C1q.
Human mesangial cells (HMC) were analyzed for their expression of 20-kDa homologous restriction factor (CD59), a glycophospholipid-anchored regulatory protein of the complement cascade. Flow cytometric analysis showed that CD59 was expressed on the HMC membrane and, following the activation of the terminal pathway complement components, CD59 expression on the HMC membrane increased. Northern blot analysis showed that CD59 mRNA levels increased by complement activation. Of interest, CD59 mRNA levels increased by soluble complement activation product, zymosan-activated C8-depleted serum, but not zymosan-activated C5-depleted serum. This effect of soluble complement activation product was due to the presence of the action of C5a. Thus, recombinant C5a increased CD59 mRNA levels. The capacity of CD59 to reinsert into rat E and inhibit C-mediated lysis was inhibited by mAb against CD59 (1F5). Metabolic labeling using [35S]cysteine showed that the molecular mass of CD59 in HMC was 20 kDa. In conclusion, CD59 is present on HMC and the expression of CD59 is controlled by at least two steps of complement activation pathway, C5 and C8.