Genetic analysis of human immunodeficiency virus in Abidjan, Ivory Coast reveals predominance of HIV type 1 subtype A and introduction of subtype G.

To better understand the molecular epidemiology of HIV genetic diversity in Abidjan, Ivory Coast, we performed a genetic analysis of 170 HIV-1-seropositive specimens representing newly diagnosed tuberculosis patients (n = 143) and women monitored in a mother-to-child transmission cohort study (n = 27). Preliminary screening with RFLP presumptively classified 162 (95.3%) of these as subtype A. The envelope region of 108 specimens was subtyped by sequence analysis: 102 (94.4%) were subtype A, 2 (1.9%) were subtype D, and 4 (3.7%) were subtype G. Subtyping gag and env regions of the genome suggested that five of the six nonsubtype A isolates exhibited a potentially mosaic structure. A comparative phylogenetic analysis of HIV-1 subtype A C2V3 from 27 Ivory Coast and 21 Ugandan sequences revealed a striking clustering among Ivory Coast variants, and an independent segregation from Ugandan subtype A. Despite independent clustering with other subtype A specimens, limited variability of the V3 loop apex was observed; the globally predominant V3 motif, GPGQ, represented 90.1% of the HIV-1 strains. This study demonstrates that clade A is the predominant HIV-1 subtype in HIV-seropositive individuals in Abidjan, Ivory Coast and that these strains are phylogenetically distinct from other subtype A strains observed in East Africa.

Differentiation of an immature T cell line: a model of thymic positive selection.

Thymocyte differentiation is dependent upon recognition of major histocompatibility complex (MHC) molecules on thymic stroma, a process called positive selection. Here we describe an immature CD4+8+ T cell line derived from a TCR transgenic mouse that differentiates into CD4+8- cells in response to antigen and nonthymic antigen-presenting cells. When injected intrathymically, these cells differentiate in the absence of antigen. The ability of immature T cells to recognize MHC molecules in the absence of foreign antigen in the thymus can thus be attributed to a unique property of thymic antigen-presenting cells. These studies also demonstrate the phenotypic and functional changes associated with TCR-mediated T cell maturation and establish an in vitro model system of positive selection.

Immunologic characterization of jird lymphocyte responsiveness to Brugia pahangi ribosomal protein S13.

Ribosomal protein S13 of the nematode Brugia pahangi is recognized by B and T cells from parasite-infected animals. To identify helper T cell sites on the protein, 15 overlapping synthetic peptides spanning the entire molecule (Bp17.4) were tested for their ability to stimulate lymph node and spleen cells of peptide-immunized and recombinant antigen-immunized jirds. Lymph node cells from animals immunized with peptides 6, 8, 9, 13, and 14, corresponding to Bp17.4 amino acids (AA) 50-70, 70-90, 80-100, 120-140, and 130-150, respectively, showed strong and specific responses to the homologous peptide, while only those lymph node cells from jirds immunized with peptides 8, 9, 13, and 14 proliferated in response to Bp17.4. These results suggest the existence of at least two T cell epitopes. Lymph node cells from infected jirds also responded to these peptides and to Bp17.4 (80,000 cpm). In contrast to the lymph node cells, spleen cells from microfilaria-positive animals failed to mount significant responses to any of the peptides or to Bp17.4. Splenic T cell responsiveness was restored upon removal of nylon wool adherent cells, suggesting active regulation of Bp17.4 reactivity. In liquid-phase competitive inhibition immunoassays, peptides 1 (AA 1-30) and 6 (50-70) blocked antibody binding and, therefore, these regions contain conformational antibody-binding sites. This model system should prove useful for analyzing regulation of epitope-specific responses in experimental filariasis.

Identification of a window period for susceptibility to dual infection with two distinct human immunodeficiency virus type 2 isolates in a Macaca nemestrina (pig-tailed macaque) model.

The potential to establish dual retroviral infections was investigated in this study. Groups of macaques infected with human immunodeficiency virus type 2 (HIV-2) isolate (either GB122 or CDC77618) were exposed to the other virus at 2, 4, 8, 12, 14, or 72 weeks after primary inoculation. Dual infections were established in macaques simultaneously exposed to both viruses. In other groups, secondary infections were observed only if challenge occurred at early intervals after primary infection but before a full seroconversion. Polymerase chain reaction and virus-isolation data demonstrated that challenges at 8, 12, 14, or 72 weeks after infection with the initial isolate failed to result in a dual infection. Anti-HIV-2 serologic titers, CD4 levels, virus burden, and the ability to superinfect peripheral blood mononuclear cells in vitro were not correlated with susceptibility to or protection from secondary challenges in this investigation. These findings demonstrate a window period for susceptibility to dual infection and indicate that protection from retroviral infection may be achievable.

Viral and immunologic examination of human immunodeficiency virus type 1-infected, persistently seronegative persons.

Persons who were human immunodeficiency virus type 1 (HIV-1)-infected but who remained persistently seronegative (HIPS) on HIV-1 antibody tests were examined through AIDS case surveillance. Six such individuals (HIPS-1 to -4, -7, and -9) were examined to determine whether their persistent seronegativity was attributable to immune dysfunction or infection with atypical HIV. Of the 6, 4 had antibody titers to at least 1 other common pathogen. In vitro stimulation of peripheral blood mononuclear cells from HIPS-4 and HIPS-7 with pokeweed mitogen or phosphorothioate oligodeoxynucleotide (direct B cell mitogen) did not produce HIV-1-specific antibody. Reconstitution experiments with recombinant interleukin (rIL)-4 and rIL-12 also had no impact on antibody production. Virus isolates from HIPS-4 and -9 were R5X4-tropic, whereas HIPS-7 was CCR5-tropic only. Sequence analysis of long terminal repeat, p24, and env gp41 did not reveal any specific mutation, and phylogenetic analysis confirmed that all 6 virus specimens were HIV-1 subtype B. These data suggest that the lack of a detectable antibody response in these patients may be the result of immune dysfunction.