Antibody from patients with acute human immunodeficiency virus (HIV) infection inhibits primary strains of HIV type 1 in the presence of natural-killer effector cells

Abstract

The partial control of viremia during acute human immunodeficiency virus type 1 (HIV-1) infection is accompanied by an HIV-1-specific cytotoxic T-lymphocyte (CTL) response and an absent or infrequent neutralizing antibody response. The control of HIV-1 viremia has thus been attributed primarily, if not exclusively, to CTL activity. In this study, the role of antibody in controlling viremia was investigated by measuring the ability of plasma or immunoglobulin G from acutely infected patients to inhibit primary strains of HIV-1 in the presence of natural-killer (NK) effector cells. Antibody that inhibits virus when combined with effector cells was present in the majority of patients within days or weeks after onset of symptoms of acute infection. Furthermore, the magnitude of this effector cell-mediated antiviral antibody response was inversely associated with plasma viremia level, and both autologous and heterologous HIV-1 strains were inhibited. Finally, antibody from acutely infected patients likely reduced HIV-1 yield in vitro both by mediating effector cell lysis of target cells expressing HIV-1 glycoproteins and by augmenting the release of beta-chemokines from NK cells. HIV-1-specific antibody may be an important contributor to the early control of HIV viremia.

FIG. 1

Inhibition of HIV-1 due to 10% plasma from acutely infected patients (Pt.) with (solid lines) or without (broken lines) NK effector cells (E:T = 10:1). CD4⁺ lymphocytes were infected for 48 h prior to the addition of plasma and effector cells, and p24 antigen was determined subsequently in supernatant fluids on the days indicated. Percent inhibition = {1 − ([p24_i]/[p24_u])} × 100, where [p24_i] and [p24_u] are the concentrations of supernatant fluid p24 produced by HIV-1-infected CD4⁺ lymphocytes in the presence of plasma from acutely infected patients or from uninfected controls, respectively. This formula was applied to the calculation of virus inhibition due to antibody alone and due to antibody combined with effector cells. Each error bars represents the standard error of two to five experiments.

FIG. 2

(a) IgG from acutely infected patients inhibits HIV-1 in the presence of NK effector cells. IgG from two acutely infected patients or HIV-seronegative controls without or with NK effector cells was added to CD4⁺ lymphocytes infected with HIV-1 for 48 h. Supernatant fluid p24 was sampled 7 days later; similar results were obtained when p24 was sampled at 5 days. Data shown are representative of two separate experiments. (b) The antiviral activity of antibody was removed by adsorbing with cells expressing HIV-1 surface glycoproteins (CEM₂₁₃ cells). Prior to measurement of antiviral activity in the presence of NK effector cells, plasma pooled from HIV-seronegative controls or from acutely infected patients (pool A, consisting of plasma from patients 5 and 9; pool B, consisting of plasma from patients 6 and 10) was left unadsorbed or (for patient plasma) was adsorbed with either untransfected CEM cells or CEM₂₁₃ cells. p24 was sampled from supernatant fluid 10 days after the addition of plasma and effector cells; similar results were obtained when p24 was sampled at 6 days. Data shown are representative of two separate experiments.

FIG. 3

Evolution of antiviral antibody response and plasma HIV RNA during acute infection. Solid lines, percent inhibition (calculated as described for Fig. 1 and in the text) for 10% plasma in the presence of NK effector cells; broken lines, HIV RNA level. Multiple samples from individual patients were assayed for virus inhibition in parallel (in three separate assays), using single effector cell and target cell donors in each assay (effector cells and target cells were from different donors, and the E:T ratio was 10:1). Parallel assays were run once for each sample; however, the first time points from patients (Pt.) 1, 6, and 7 represent the mean values from an additional one to four assays.

FIG. 4

Antiviral antibody activity in plasma from acutely infected patients is inversely associated with plasma HIV-1 RNA level. Percent inhibition of viral yield by 10% patient plasma (from the earliest time point tested) and NK effector cells from uninfected donors is shown as a continuous variable with linear regression line.

FIG. 5

Plasma samples from acutely infected patients mediate cytotoxicity of HIV-1 env-transfected CEM cells in the presence of PBMC effector cells. ⁵¹Cr-labeled CEM₂₁₃ target cells were incubated in triplicate with serial dilutions of patient plasma and with PBMCs from a healthy donor in a 4-h ⁵¹Cr release assay; mean counts were used to calculate percent cytotoxicity as described in the text. Plasma samples were obtained at different days (d. 2, d. 12, etc.) following the onset of symptoms of acute HIV infection or, in the case of patients (Pt.) 5 and 8, following a known exposure to HIV. Also shown (insets) are the HIV RNA levels from plasma obtained on each day.

FIG. 6

(a) Medium conditioned by an interaction between antibody, NK cells, and HIV envelope-expressing target cells inhibits a primary, R5 strain of HIV-1. Conditioned medium was obtained from flasks containing CEM₂₁₃ target cells and either NK effector cells from a healthy donor plus IgG from a pool of acutely infected patients (Pt.), IgG from acutely infected patients without NK effector cells, or NK effector cells plus IgG from HIV-seronegative donors. Percent inhibition was calculated by the formula 100 × {1 − ([p24_cm]/[p24_vc])}, where [p24_cm] is the concentration of p24 obtained from supernatant fluid of freshly infected CD4⁺ lymphocytes after 5 days incubation with conditioned medium, and [p24_vc] is the concentration of p24 obtained with supernatant fluid of freshly infected CD4⁺ lymphocytes after 5 days incubation with medium alone (i.e., virus control). Data represent means ± standard errors of 10 experiments in the case of effector cells and patient IgG; effector cells plus HIV-seronegative IgG and patient IgG without effector cells were included in four and five of these experiments, respectively. (b) Antibodies against β-chemokines inhibit the antiviral effect of conditioned medium. Medium conditioned with CEM₂₁₃ target cells, IgG from acutely infected patients, and NK effector cells was incubated with HIV-infected CD4⁺ lymphocytes. The conditioned medium was used without adsorption or after adsorption with normal goat serum, goat anti-RANTES antibody, goat anti-MIP-1α antibody, or goat anti-MIP-1β antibody. Data represent means ± standard errors of three experiments.