0000000000994215
AUTHOR
Marcus Kaul
Disulfide bridge formation between C1q and IgG in vitro.
The globular heads of C1q are known to possess free-SH groups. Here we show that these groups, which are concealed in the native molecule, are exposed by interaction of C1q with dialysis membrane. During iodination, I+ and I2 oxidize these sulfhydryls to produce disulfide-linked C1q aggregates. Approximately 15% of C1q bound to immunoglobulin aggregates is resistant to high conductivity elution and reducing agent is required to release it. These data show that dialysis, adsorption to Ig and iodination of C1q result in structural and functional changes in the molecule, and suggest a mechanism by which these changes occur. Disulfide bridging between C1q and IgG in vitro suggests that this may…
Human macrophages simultaneously express membrane-C1q and Fc-receptors for IgG
Membrane C1q (mC1q) of macrophages (MPhi) is a precursor of the IgG-binding serum protein C1q. Thus, mC1q potentially provides one of several Fcgamma binding sites of mature MPhi and we analyzed whether simultaneous expression occurs of established receptors for IgG, FcgammaRI, II, and III, and mC1q during in vitro differentiation of MPhi. Using flow cytometry, immunoprecipitation combined with Western blotting and Northern blot analysis mC1q was hardly detected in freshly isolated blood monocytes, but increasingly in developing monocyte-derived MPhi. Laser scanning fluorescence microscopy confirmed the membrane localization of mC1q. Two-color-staining flow cytometry experiments indicated t…
Secreted proteophosphoglycan of Leishmania mexicana amastigotes activates complement by triggering the mannan binding lectin pathway.
Cutaneous lesions induced by infection of mice with the protozoan parasite, Leishmania mexicana, contain abundant amounts of a high molecular mass proteophosphoglycan (PPG), which is secreted by the amastigote stage residing in phagolysosomes of macrophages and can then be released into the tissue upon rupture of the infected cells. Amastigote PPG forms sausage-shaped but soluble particles and belongs to a novel class of serine-rich proteins that are extensively O-glycosylated by phosphooligosaccharides capped by mannooligosaccharides. The purified molecule is shown here to efficiently activate complement (C) and deplete hemolytic activity of normal serum and may prevent the opsonization of…
Expression of membrane C1q in human monocyte-derived macrophages is developmentally regulated and enhanced by interferon-γ
The present study investigated when during "in vitro" maturation macrophages (MPhi) express membrane C1q (mC1q), and whether cell activation affects expression and function of mC1q. Although C1q mRNA was repeatedly detected in freshly isolated monocytes using reverse transcriptase-polymerase chain reaction, C1q protein was observed only in developing MPhi from day 1 to 4 on using immunodetection and flow cytometry. However, the quantity of mC1q and other MPhi membrane proteins differed strikingly in cells from different donors. We report here for the first time that CD14(+) and CD14(-) mC1q-bearing MPhi can develop, and that interferon-gamma increases mC1q display at the cell surface, and m…
Dissection of C1q Capability of Interacting with IgG
Abstract C1q-bearing immune complexes have been observed in diseases such as rheumatoid arthritis and human immunodeficiency virus infection-associated neuropathy. For the purpose of understanding better the phenomenon of C1q-bearing immune complexes, we investigated the constancy of the C1q-IgG interaction. An enzyme-linked immunosorbent assay was developed in which wells were coated with IgG to mimic antigen-complexed IgG. Serial dilutions of C1q were applied for distinct time intervals, and bound C1q was detected either directly or after exposure to one of several elution buffers. Our results show that a part of C1q attached to IgG forms a tight association that is not reversible under t…