PubMed · 7383120
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G Camussi, F C Cappio, C Tetta. 1980-07-31. Complement-induced granulocyte aggregation.. https://doi.org/10.1056/nejm198007313030519
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Intravenously applied human IgG has beneficial effects in treating inflammatory diseases, presumably because it has a complement attenuating role. This role of IgG was studied in vitro by following C3 activation and inactivation in sera that were supplemented with exogenous human IgG and incubated with immune aggregates. IgG added at 2 to 10 mg/mL stimulated the physiologic inactivation of C3b-containing complexes twofold to threefold in 20% sera. This, in turn, lowered the overall C3 activation by 28%, as new C3 convertases primarily assembled on C3b-containing complexes. Exogenous IgG (5 mg/mL) also stimulated inactivation of purified C3b2-IgG complexes, whereby their half-life dropped from 3-4 to 1.5 minutes in 20% serum. IgG appeared to act like a modulator of factor H and I because it did not stimulate inactivation of C3b-containing complexes in factor I-deficient serum. Thus, the known partial protection of C3bn-IgG complexes from inactivation by factor H and I was downregulated by high concentrations of IgG. The ability of high doses of IgG to stimulate complement inactivation is a novel regulatory role of IgG. This may be one of the molecular principles for its therapeutic efficacy in treating complement-mediated inflammations.
HIV-1-infected quiescent CD4+ cells harbor the virus in an inactive state until subsequent activation. The possibility that HIV-1 itself and the virus envelope glycoprotein 120 (gp120) might be important agents of this activation was investigated. The present data indicate that binding of heat-inactivated HIV-1 (iHIV-1) to infected resting PBMCs was sufficient to activate NF-kappa B and AP-1, to induce transition from the G0/G1 stage of the cell cycle to the S/G2/M stage, to induce cell surface expression of CD25, to stimulate provirus integration, and to commit cells to produce virus. The cumulative amount of HIV-1 produced by iHIV-1-stimulated cells strictly depended on the concentration of p24gag in the virion preparations used for stimulation. Moreover, virus production was not evidenced in infected resting cells exposed to iHIV-1 previously incubated with soluble CD4 (sCD4), indicating that activation requires a contact between HIV-1 envelope glycoproteins and cell surface CD4. Although soluble gp120 did not stimulate virus production, we found that transition to the S/G2/M stage of the cell cycle, cell surface expression of activation Ags, and virus production were stimulated by cross-linking of CD4 by gp120-anti-gp120 immune complexes. Finally, incubation of gp120-anti-gp120 immune complexes with sCD4 inhibited these effects. These findings suggest that virions and gp120 anti-gp120 immune complexes found in infected patients at all times of infection can stimulate virus production in CD4+ cells harboring HIV-1 in an inducible state.
Our previous results showed that neutrophil secondary granule release, indicated by release of lactoferrin, was a slow process when induced by IgA immune complexes (IC) formed in heat-inactivated serum, but became very fast if IgA IC were formed in normal human serum. This phenomenon did not apply to the IC of other Ab isotypes. In this paper, we demonstrate that the fast lactoferrin release is caused by complement, mainly due to the deposition of C3b and iC3b on IgA IC. Either CR1 or CR3 can mediate the response and both receptors have to be blocked to prevent it. Complement also influences FcalphaR-mediated lactoferrin release, in that this is enhanced by the anaphylatoxin peptides, C5a and C5a(desArg). Divalent cations are required for FcalphaR and CR3- but not for CR1-mediated lactoferrin release. Genistein, a protein tyrosine kinase inhibitor, totally inhibits FcalphaR-mediated response, but has little effect on CR1-mediated response. Therefore, it is clear that different pathways of intracellular signaling are utilized. In addition, stimulation through FcalphaR promotes the receptor up-regulation, which is abolished by the presence of EDTA or genistein.