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OBJECTIVE To analyse the ability of different HIV-1 and HIV-2 isolates to activate the complement system. DESIGN H9 cells chronically infected with various HIV isolates and the corresponding purified viruses were tested for complement activation. To identify the molecules responsible for complement activation on the surface of infected cells, the expression of complement inhibitors/regulators and viral proteins on the cell surface was analysed. METHODS C3 deposition on the cell surface and the expression of viral and cellular antigens were determined by flow cytometry analysis. Complement activation by purified viruses was measured using a complement consumption assay and a C1 activation assay. RESULTS H9 cells infected with different HIV-1 and HIV-2 isolates showed varying degrees of complement activation on the cell surface, ranging from strong activation and deposition of large amounts of C3 to no increased C3 deposition compared to uninfected cells. The C3 deposition was eliminated by EDTA and reduced in the presence of EGTA. In contrast, all purified viral isolates tested activated the complement system in a comparable manner. While the expression of MCP, DAF and CD59 was not modified after infection with different viral isolates, the reaction of the infected cells with a monoclonal antibody (3D6) directed against a gp41 epitope (amino acids 601-620) was found to correlate with the complement activation on the cell surface. CONCLUSIONS Some HIV-1 as well as HIV-2 isolates activate the complement system on the surface of infected cells independent of anti-HIV antibodies, while other isolates fail to do so. Complement activation on the cell surface is mediated by the alternative and, to a lesser extent, the classical pathway. The differences in complement activation on the cell surface are not caused by a modified expression of membrane-bound complement inhibitors/regulators. C3 deposition on the cell surface correlates with the expression of an epitope lying within the major complement activating domain of gp41 (amino acids 591-620). These results suggest a role of gp41 for complement activation on HIV-infected cells as has been described previously for purified HIV.

OBJECTIVE To evaluate changes in serum HIV p24-antigen levels in a subset of patients who participated in a European/Australian double-blind, placebo-controlled trial evaluating the efficacy of zidovudine (250 mg every 6 h) alone or in combination with acyclovir (800 mg every 6 h) in patients with AIDS, AIDS-related complex (ARC) or Kaposi's sarcoma (KS). DESIGN Double-blind, placebo-controlled randomized clinical trial of less than or equal to 6 months' therapy. SETTING Samples were obtained from patients attending teaching hospital outpatient clinics in seven European countries and Australia. SUBJECTS One hundred and ninety-seven HIV-infected patients (60 with AIDS and 137 with ARC or KS). MAIN OUTCOME MEASURES Serum HIV p24-antigen levels measured using the Abbott HIV solid-phase enzyme immunoassay. RESULTS Of 76 ARC/KS patients who were initially HIV p24-antigen-positive, one out of 25 randomized to placebo, eight out of 23 to zidovudine and 11 out of 28 to the zidovudine/acyclovir combination became antigen-negative. The proportion of patients who became antigen-negative was significantly higher in both the zidovudine group (P = 0.016) and the zidovudine/acyclovir group (P = 0.004), compared with the placebo group. There were no statistical differences between the zidovudine and the zidovudine/acyclovir groups. During the trial p24-antigen levels in the zidovudine-treated patients reached their minimum after 4-8 weeks of therapy, and tended to increase gradually thereafter. Disease progression occurred irrespective of whether p24-antigen levels declined during therapy. No association between p24-antigen responses to therapy and baseline disease stage, Karnofsky score or baseline CD4 cell count was detectable. CONCLUSION Acyclovir does not potentiate the effect of zidovudine on p24-antigen levels. Change in antigen level in response to antiviral therapy needs further investigation before it is used as a surrogate marker for clinical efficacy of antiviral therapy.

In a multicenter collaborative study a new second-generation HIV-1 antibody enzyme immunoassay (Abbott recombinant HIV-1 EIA) using Escherichia coli-expressed recombinant p24 and p41 proteins as solid-phase antigens was compared with the first-generation H9 cell-line-based Abbott HIV-1 EIA. The results of the confirmatory assays (Western blot, immunofluorescence), combined with clinical information, were used as the reference standard for the detection of HIV-1 antibodies in 10,676 random blood donor serum specimens, in a panel of 840 specimens from symptomatic and asymptomatic patients and a total of 63 serial blood specimens from 23 people at risk. With fresh blood donor sera, the specificity of the first-generation assay ranged between 99.54 and 99.76% (95% confidence limits, CL) compared with 99.81-99.95% (95% CL) for the second-generation EIA. With panel specimens the recombinant HIV-1 EIA achieved an overall sensitivity of 100% and a specificity range of 98.3-99.7% (95% CL); the corresponding sensitivity and specificity ranges observed for the first-generation EIA were 98.0-99.5% (95% CL) and 94.3-96.8% (95% CL), respectively. The improved sensitivity for the second-generation assay was confirmed by testing serial samples from seroconverting patients. The use of recombinant proteins eliminated non-specific reactions due to class II human leukocyte antigen (HLA)-directed antibodies.