Human Immunodeficiency Virus (HIV)-Positive Sera Obtained Shortly after Seroconversion Neutralize Autologous HIV Type 1 Isolates on Primary Macrophages but Not on Lymphocytes

Abstract

The aim of this study was to analyze the role of humoral immunity in early human immunodeficiency virus (HIV) infection. As neutralizing activities in HIV-positive sera are rarely detectable earlier than 9 to 12 months after infection using primary lymphocytes as target cells in neutralization assays, humoral immunity is generally thought not to contribute significantly to early virus control in the patients. Besides lymphocytes, cells of the monocyte/macrophage lineage are known to be important target cells for HIV in vivo during the establishment of the infection. Therefore, we studied the neutralization of early primary HIV isolates by autologous serum samples using primary macrophages as target cells in the neutralization assays. We analyzed neutralizing activities against the autologous HIV-1 isolates in 10 patients' sera taken shortly after seroconversion, both on primary macrophages and, for comparison, on lymphocytes. Viruses were isolated and expanded in primary mixed cultures containing macrophages and lymphocytes in order to avoid selection for one particular cell type. All viruses replicated to different degrees in macrophages and lymphocytes; nine had a nonsyncytiuminducing phenotype, and one was syncytium inducing. The detection of neutralizing antibodies in acute primary HIV infection depended on the target cells used. Confirming previous studies, we did not find neutralizing activities on lymphocytes at this early time point. In contrast, neutralizing activities were detectable in the same sera if primary macrophages were used as target cells. Differences in neutralizing activities on macrophages and lymphocytes were not due to different virus variants being present in the different cell systems, as gp120 sequences derived from both cell types were homogeneous. Neutralization activities on macrophages did not correlate with the amount of ␤-chemokines in the sera. As affinity-purified immunoglobulin G preparations from an early patient serum also exhibited neutralization of the autologous virus isolate on primary macrophages, but not on lymphocytes, neutralization is very likely due to antibodies against viral epitopes necessary for infection of macrophages but not for infection of lymphocytes. Our data suggest that, along with cellmediated immunity, humoral immunity may contribute to the reduction of primary viremia in the patient. This was further supported by a certain association between neutralizing antibody titers on macrophages and viral load in the patients.

Involvement of FcγR I (CD64) in the Mechanism of HIV-1 Inhibition by Polyclonal IgG Purified from Infected Patients in Cultured Monocyte-Derived Macrophages

“…The two previous reports analyzing neutralization of macrophage infection have found that Fab have similar inhibitory activity than their corresponding whole IgG (15)(16). Such discrepancies between these previous results and our findings could not be attributed to degradation, dilution, or loss of material resulting from enzymatic treatment of our Fab or F(abЈ) 2 preparations as these fragments conserved their neutralizing potency when PBMC were used as HIV-target cells.…”

“…Contrary to previous reports (15)(16), when MDM are used as target cells, the neutralizing activity of the Fab or F(abЈ) 2 of polyclonal IgG was reduced to the inhibitory activity detected when PBMC are the HIV-target cells in the neutralization assay.…”

“…The discrepancy could neither be related to the type of assay used, as we have also detected a great difference in the inhibitory activity between whole IgG and Fab or F(abЈ) 2 in the multiple round neutralization assay, similar to the assay used by Zhuge et al (15) (15) used sera and two purified IgG samples obtained from macaques, 6 mo after SIV inoculation while our polyclonal IgG samples were obtained from asymptomatic individuals collected after a mean duration of 7 years of infection (15). It is noteworthy that Ruppach et al (16) have adjusted the amounts of IgG and Fab to the amount of IgG corresponding to 10% patient serum estimated by SDS-PAGE. In our neutralizing experimental conditions, our Fab or F(abЈ) 2 are also capable of completely inhibiting HIV replication in MDM when used at such high concentrations (corresponding to 10% IgG in the serum).…”

“…Previous studies have shown that, when macrophages are used as target cells instead of the autologous blood lymphocytes, an increased efficiency, at least 100-fold, of the neutralizing titer was observed for plasma or sera from SIV-infected macaques or HIVinfected patients (15)(16). Ruppach et al (16) have observed autologous neutralizing activities on primary human macrophages but not on lymphocytes when analyzing sera from early infected individuals (Ͻ12 mo after seroconversion).…”

Human Immunodeficiency Virus Type 1envClones from Acute and Early Subtype B Infections for Standardized Assessments of Vaccine-Elicited Neutralizing Antibodies

“…These concerns are diminished when one considers that very little neutralizing activity was detected against Env-pseudotyped viruses when assayed with serum samples from recipients of a prototypic monomeric gp120 immunogen (Table 6). Differences in neutralization sensitivity between viruses made in 293T cells and PBMC might be explained by one or more factors: (i) the relative ease of neutralizing a single clone compared to a viral quasispecies, (ii) differences in the composition of proteins on the surface of the target cells used for infection (93), (iii) glycan composition and number of Env glycoprotein spikes on the virus surface, and/or (iv) factors associated with different adhesion molecules and other cellular proteins that become embedded on the virus surface after assembly and release from various cell types (32,41,90,112). Results of a multicenter comparative assay study indicated that differences in neutralization sensitivity are unrelated to the use of JC53-BL cells compared to PBMC as targets for infection, since similar results were obtained in both cases (Montefiori et al, unpublished data).…”