Human immunodeficiency virus type 1 (HIV-1)-seronegative injection drug users at risk for HIV exposure have antibodies to HLA class I antigens and T cells specific for HIV envelope.

The question of whether persistently seronegative persons at high risk for human immunodeficiency virus type 1 (HIV-1) infection exhibit HIV-1-specific T cell responses and antibodies to HIV-1 envelope epitopes shared with selected HLAs was assessed. These antibodies are not detectable by conventional serologic methods. Envelope-specific helper T (Env-Th) cell responses and antibodies specific for the HIV/HLA epitopes were studied in 21 HIV-1-negative injection drug users (IDUs). HIV/HLA antibodies were detected in 7 (33.3%) of 21 IDUs and 4 (4.3%) of 94 low-risk controls. Env-Th cell responses were detected in 16 (76.2%) of 21 IDUs and in 2 (3.1%) of 65 low-risk controls. All HIV/HLA antibody-positive IDUs also had Env-Th cell responses. These findings confirm the presence of HIV-1-specific immunity in conventionally seronegative individuals. Further characterization of these responses could provide the basis for new preventive strategies.

Human antibodies to immunodominant C5 region of HIV-1 gp120 cross-react with HLA class I on activated cells.

Cross-reactive antibodies to HLA class I and HIV-1 gp120 were detected in the sera of HIV-1-positive individuals, and were found to share the same epitope specificity as a gp120-HLA class I cross-reactive monoclonal antibody (M38). The amino acid residues of HLA recognized by both M38 and the patient antibodies occur as a clustered pair in the HLA-C alpha 1 domain. These sequences (KYKR and RKLR) are shared by almost all HLA-C alleles and are available to antibody binding only on beta 2-microglobulin-dissociated HLA heavy chains expressed on activated cells. Similar to M38, the antibody-binding sites on HIV-1 gp120 were mapped to two noncontiguous stretches of amino acids (KYK and KAKR), which flank a hydrophobic area of the immunodominant C5 region involved in gp41 binding. Serum antibodies immunoaffinity purified on synthetic HLA and gp120 peptides representing the M38-reactive regions were shown to bind to both HLA and gp120 in Western blot, as well as to membrane-bound HLA heavy chains, and to exhibit selective complement-mediated lysis of activated T cells. No serum antibodies could be detected that bind to the gp120 C5 region (peptide IEPLGVAPT) flanked by the two HLA-like sequences.

A comparative study of natural killer cell activity, lymphoproliferation, and cell phenotypes in nonhuman primates.

Three different species of nonhuman primates (baboons [Papio hamadryas], rhesus monkeys [Macaca mulatta], and African green monkeys [Cercopithecus aethiops]) were evaluated for their natural killer cell activity, and for the ability of their peripheral blood mononuclear cells to proliferate in response to known mitogens (concanavalin A, phytohemagglutinin, and pokeweed mitogen) and to react with a panel of mouse monoclonal antibodies directed against human leukocyte surface antigens. Rhesus monkeys displayed the highest natural killer cell cytotoxic activity (185.7 +/- 33 lytic units) compared with those of baboons (83.8 +/- 19 lytic units) and of African green monkeys from West Africa (39.08 +/- 8 lytic units) and from the Caribbean basin (37.9 +/- 9 lytic units). No correlation was observed between the natural killer cell cytotoxic activity and the percentage of CD16+ natural killer cells among the three species studied. High spontaneous proliferative capacity was observed in African green monkeys obtained from West Africa compared with those of the other species studied. Although no significant differences were noted in T and B cell mitogen-induced in vitro proliferation, baboon mononuclear cells were less responsive to concanavalin A (stimulation index of 16 +/- 3 [mean +/- standard error of mean]) than to phytohemagglutinin (stimulation index of 47 +/- 12). However, rhesus and African green monkey cells proliferated more efficiently in response to concanavalin A. Unlike in human beings where the ratio between helper-inducer (CD4+) and cytotoxic-suppressor (CD8+) T-lymphocytes is generally greater than 1, the CD4+/CD8+ ratios in baboons and rhesus and African green monkeys were 0.58, 0.69, and 0.35, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Augmentation of cellular immune function during the early phase of zidovudine treatment of AIDS patients.

Twenty-five patients with AIDS in AIDS Clinical Trials Group Protocol 002 were treated with either low or high dosages of zidovudine. This resulted in moderate, transient increases by 10 and 20 weeks in lymphocyte blastogenesis and interferon-gamma (IFN-gamma) production in vitro in response to phytohemagglutinin with and without recombinant interleukin-2. Immune responses to cytomegalovirus and herpes simplex virus type 1 antigens were augmented less frequently during therapy. Natural killer (NK) cell lysis of uninfected and human immunodeficiency virus-infected cells was also transiently increased by 10 and 20 weeks. IFN-gamma production, the only immune parameter directly associated with increases in numbers of CD4+ T cells, peaked at 10 weeks of treatment. The limited efficacy of zidovudine treatment in AIDS patients is associated with moderate, temporary increases in nonspecific and herpesvirus-specific T lymphocyte responses and NK cell function.

Monoclonal anti-idiotype induces protection against the cytotoxicity of the trichothecene mycotoxin T-2.

An IgG1 mAb, designated HD11, specific for the trichothecene mycotoxin T-2 and capable of neutralizing its cytotoxicity was used to generate a syngeneic monoclonal anti-Id antibody. The generated anti-Id mAb, designated DE8, specifically bound to HD11 anti-T-2 mAb, and not to IgG1 mAb of irrelevant specificity or to normal mouse Ig. DE8 inhibited the binding of HD11 anti-T-2 to T-2-BSA-coated plates, whereas a control anti-Id mAb did not, suggesting recognition of an Id determinant associated with the T-2 binding site of HD11. Moreover, the binding of HD11 to DE8 and that of DE8 to HD11 were specifically inhibited by free T-2 mycotoxin. DE8 mAb was efficient in abrogating the protective effect of HD11 in the cytotoxicity of T-2 on the human epidermoid carcinoma cell line Hep-2. In vivo immunization of BALB/c mice with DE8 conjugated to KLH induced an anti-T-2 antibody titer comparable to that obtained with T-2-OVA immunization, whereas immunization with unconjugated DE8 resulted in a lower titered anti-T-2 response. Immunization with DE8-keyhole limpet or with unconjugated DE8 induced anti-T-2 antibody responses characterized by expression of "HD11-like" Id and by protection against T-2 cytotoxicity. However, the T-2-OVA-induced anti-T-2 response lacked the HD11+ Id and was only partially protective against T-2 cytotoxicity. This represents the first demonstration of the use of an anti-Id based vaccine in the in vivo induction of a protective antibody response against the cytotoxicity of a nonproteinaceous, small m.w. biologic toxin, whose very toxic nature precludes its use as the immunogen.

Natural killer cell responses in homosexual men with early HIV infection.

Natural killer (NK) cells may be of significance in host defense against viral infections. In the present study, NK cell function was examined in relation to different phases of human immunodeficiency virus (HIV) infection. Peripheral blood mononuclear cells were tested for NK cell activity using K562 cell targets in a 51Cr-release assay. NK cell responses of 26 HIV-seronegative homosexual men were not significantly different from those of 30 heterosexual controls. NK activity was significantly lower in cells from 32 homosexual men with documented, early-phase HIV infection (average of 14 months; range of 3-27 months) as compared with that of seronegative men. The NK cell response decreased with time, since men within the first year of infection (n = 15; average of 7.8 months; range of 3-12 months) had greater NK cell activity than did those with longer duration of infection (n = 17; average of 18.3 months; range of 13-27 months). The decrease in NK cell activity did not correlate with altered numbers of cells bearing CD16 (NK) markers in these subjects. NK cell-mediated lysis and cell numbers were most severely depressed in a separate group of HIV-seropositive men who had acquired immune deficiency syndrome (AIDS). In vitro treatment with alpha-interferon (alpha-IFN) significantly enhanced NK activity of effector cells obtained from men within the first year of HIV infection but not in those with longer-term infection. Our results indicate that NK cell function decreases over time within the first 2 years of HIV infection in homosexual men, and is lowest in HIV-seropositive men with overt AIDS.(ABSTRACT TRUNCATED AT 250 WORDS)

Association of alpha interferon production with natural killer cell lysis of U937 cells infected with human immunodeficiency virus.

Mononuclear leukocytes from human immunodeficiency virus (HIV)-seronegative and -seropositive homosexual men lysed HIV-infected U937 cells to a significantly greater degree than uninfected U937 cells. Depletion of cell subsets with monoclonal antibodies and complement indicated that the effector cells were primarily of the CD16+ phenotype. Acid-stable alpha interferon (IFN-alpha) production induced by the HIV-infected cells correlated with, although was not an absolute requisite for, preferential lysis of the infected targets. The activity of these CD16+, natural killer (NK) cells decreased in relation to the duration of HIV infection and the presence of acquired immunodeficiency syndrome. Pretreatment of peripheral blood mononuclear cells from HIV-seronegative subjects, but not HIV-seropositive men, with IFN-alpha or recombinant interleukin-2 enhanced lysis of both uninfected and HIV-infected U937 cells. These results suggest that IFN-alpha-associated, NK-like mechanisms are active in the cytotoxic response against HIV-infected cells and that HIV infection results in an early and progressive depression of such responses. Prospective investigations may be useful in determining the role of this NK cell response in the natural history and pathogenesis of HIV infection and the efficacy of therapeutic modalities.

Primary in vitro antibody response in humans: role of adherent cells in the development of haemolytic colonies.

Primary antibody response in vitro by human peripheral blood mononuclear cells (PBMC) against sheep red blood cells (SRBC) was investigated by the method of haemolytic colonies in soft agar. The response was modulated by two antagonistic populations of surface-adherent cells (AC) that could be enriched by physical means using differential adhesion to the plastic. Firmly adherent cells (AC/FA), which remained surface stuck after 18 hr, cocultured with AC-depleted PBMC, significantly inhibited the production of haemolytic colonies; AC/NR cells, which were released after this interval, strongly increased the response. The inhibition by AC/FA cells was mainly due to production of peroxides and the stimulation by AC/NR to the synthesis of arachidonic acid derivatives. When the two subpopulations were present contemporarily at the concentration shown in PBMC suspensions, the suppressive action of AC/FA overwhelmed the enhancing activity of AC/NR cells. Functional, histochemical and immunochemical data suggest that the AC/FA fraction is mainly composed of typical phagocytosing cells, whereas the AC/NR fraction contains cells of uncertain classification that do not exhibit active phagocytic activity.

The interference of antibiotics with antigen-specific antibody responses in man.

The effect of a series of antimicrobial drugs on human antigen-specific primary antibody response in vitro was investigated. Of the five agents tested, only streptomycin and gentamicin induced an appreciable reduction in the antibody response; penicillin G, rifampin and amikacin had a poor or irregular effect. The precise mechanisms of action of these substances on mammalian cells remain to be elucidated since an assessment of their capacity to interfere with the immune system is of particular importance in those patients with induced or acquired immunodeficiencies. In this respect, we provide an inexpensive and sensitive method for the preliminary screening of potentially immunosuppressive drugs.

Monocyte mediated modulation of the antibody response in vitro.

Human peripheral blood monocytes (PBMC) were isolated by Ficoll-Hypaque density gradient and then fractionated by differential adhesion to plastic surface. Adherent cell-depleted PBMC, non-readherent fraction and firmly adherent fraction so obtained from PBMC, PBMC themselves and a mixture of the above cells, were then sensitized in vitro with sheep erythrocytes (SRBC) so as to produce a primary antigen-dependent, antigen-specific antibody response. It appears that adherent cell-depleted PBMC produce about twice as many haemolytic areas as compared to total PBMC (from 43 to 85). If depleted PBMC are co-cultured with firmly adherent or non-readherent cells, the number of haemolytic areas goes down to 19 or up to 102, respectively. Functional, histochemical, immunochemical and morphological data suggest that the inhibiting firmly adherent fraction is composed of typical phagocytizing cells, while the enhancing cells of the non-readherent fraction are similar to the dendritic cells described in human blood and some lymphoid organs, which do not exhibit active pinocytic activity, but are the principal accessory cells needed to stimulate lymphocyte responses.