Peter Nara

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 nonsyncytium-inducing 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 β-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 cell-mediated 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.

Persistent HIV-2 Infection of Rhesus Macaque, Baboon, and Mangabeys

Six monkeys of three different species (mangabey, macaque and baboon) were infected with human immunodeficiency type 2 (HIV-2) NIH-DZ using intraperitoneal or intravenous injections of cell-free HIV-2 or autologous HIV-2-infected cells with no prior immunostimulation. Viral expression was demonstrated by reverse transcriptase activity in cells after coculture with human peripheral blood lymphocytes or by electron microscopy. Serum was analyzed by western blot, enzyme-linked immunosorbent assay (detection of antigen and antibody), and neutralization assay carried out using immunofluorescence techniques. The 6 inoculated animals seroconverted during the 1st month after inoculation and remained persistently infected after 6-11 months. We also observed proviral DNA by genomic analysis in the six tested samples. No sign of immunodeficiency disease has been observed so far. The data suggest that HIV-2 infection of nonhuman primates provides an acceptable animal model to investigate vaccination or specific immunotherapeutic procedures.

Short Communication: No Evidence of HTLV-3 and HTLV-4 Infection in New York State Subjects at Risk for Retroviral Infection

The primate T-cell lymphoma viruses (PTLV) are divided into six distinct species. The biology and epidemiology of PTLV-1 and PTLV-2 are very well understood. However, that of PTLV-3, 4, 5, and 6 are not. Recently, in Cameroon, three and one humans were shown to be infected with HTLV-3 and HTLV-4, respectively. We undertook a study to ascertain whether any of these two retroviruses were present in the peripheral blood mononuclear cell DNA of New York State subjects deemed at risk for PTLV infection. Samples were analyzed by PTLV-3 and PTLV-4 specific PCR assays from the following human and simian subject types: African-American medical clinic patients; HTLV EIA+, WB indeterminate blood donors; intravenous drug users; patients with leukemia, lymphoma, myelopathy, polymyositis, or AIDS; and African chimpanzees. None of the 1200 subjects was positive for HTLV-3 or 4. The data indicate that, at the time of sample collection, no evidence exists for the dissemination of HTLV-3 or 4 to New York State. Continued epidemiological studies are warranted to explore the worldwide prevalence rates and dissemination patterns of HTLV-3 and 4 infections, and their possible disease associations.

Humoral Immunity to HIV-1:

The emerging evidence that specific genomic clades of HIV-1 are improving their fitness for efficient transmission via mucosal surfaces, i. e., heterosexual routes (Cohen, 1995; Osborn, 1995; Mastro et al., 1994), is disturbing and serves as an important backdrop for this book and a discussion of the role of humoral immunity. The evolution to improved fitness for mucosal transmission does not come as a surprise to those in the comparative lentivirus field, because the animal lentiviruses are as capable of broad transmission spectrum as one finds for enveloped RNA viruses (reviewed in Nara, 1988; Nara et al., 1991). These viral pathogens can assume either a cell-free or a cell-associated state, as dictated by the social and reproductive behaviors of the species. Because of genomic plasticity, primitive retroviral ancestry, and likely evolution with the vertebrates’ innate and adaptive immune systems, various aspects of humoral host defenses may have been exploited by the virus. Insights gained over the past few years now contribute to a more complete picture and understanding of so-called “humoral immunity,” which includes both nonclonal, innate, or nonadaptive immune system and the clonal, acquired (i. e., specific), or adaptive immune system. Together, these complementary defense systems must communicate to protect infectious nonself from noninfectious self. This is accomplished through similar structural/ functional forms of nonclonal and clonal inducible soluble host defense molecules (Janeway, 1992) by providing a continuous antimicrobial state during the period of initial infection and subsequent colonization of the host. These two defense systems now appear to be more inextricably linked in their induction than previously appreciated. Thus, depending on which effect or arms are activated, and in what order, may influence the establishment of conventional T- and B-cell-type immunity.

The presence and absence of histocompatibility antigens in HIV type 1 produced by autologous blood-derived macrophages and peripheral blood lymphoblasts.

Acquisition of cellular proteins by HIV-1 virions is known to alter the physiology of the virus in vitro. Reported studies of this aspect have been largely limited to transformed T cell lines. In this study, we investigated the incorporation of major histocompatibility antigens (HLAs) on a primary macrophage-tropic isolate, HIV-1ADA, grown from autologous monocyte-derived macrophages (MDMs) and peripheral blood mononuclear cells (PBMCs). A virus precipitation assay (VPA) demonstrated that HIV-1ADA grown from PBMCs incorporated substantial amounts of HLA class I (alpha chain and beta2m) and DR antigens, comparable with a laboratory strain, HIV-1MN, grown from the same host cells. HIV-1ADA, however, grown from MDMs incorporated significantly lower amounts of HLAI and -II antigens despite the fact that the infected MDMs were found to express significant amounts of HLA antigens. The lack of incorporation of these important immunomodulatory cell surface proteins may be yet another unique characteristic of macrophage-tropic isolates and suggests a possible role in their biology and or immunology.