Presence of host ICAM-1 in laboratory and clinical strains of human immunodeficiency virus type 1 increases virus infectivity and CD4(+)-T-cell depletion in human lymphoid tissue, a major site of replication in vivo

Abstract

Human immunodeficiency virus type 1 (HIV-1) incorporates several host proteins. Earlier studies have indicated that such foreign constituents can modulate the virus life cycle, although the potential roles that these proteins might play in the viral pathology in vivo remain unclear. In an attempt to shed light on this issue, we first exposed explants of human lymphoid tissue to isogenic viruses except for the presence or absence of host-derived ICAM-1. Incorporation of ICAM-1 alone increased HIV-1 infectivity for human tonsillar tissue cultured ex vivo. This observation was made for viruses bearing distinct coreceptor utilization profiles. Conversion of LFA-1 to a high-affinity-high-avidity state for ICAM-1 further augmented the susceptibility of human tonsillar histocultures to infection by ICAM-1-bearing virions. A more massive depletion of CD4(+) T lymphocytes was seen with X4 ICAM-1/POS viruses than with isogenic ICAM-1/NEG virions. Exposure of X4 and R5 primary isolates of HIV-1 to a blocking anti-ICAM-1 antibody resulted in a decrease of virus infection. Finally, X4 and R5 virions derived from a natural human lymphoid tissue microenvironment incorporated high levels of ICAM-1. Altogether, these results indicate that the incorporation of host ICAM-1 can significantly modulate the biology of HIV-1 in a cellular milieu recognized as the major site of replication in vivo and suggest that host proteins found in HIV-1 particles may participate in the pathogenesis of this disease.

FIG. 1.

Virion-associated cellular ICAM-1 protein augments infectivity of both T-tropic and macrophage-tropic single-cycle reporter HIV-1 in human lymphoid tissue ex vivo. (A) Histocultures were mechanically disrupted to obtain cell suspensions that were processed for flow cytometric analyses. Single-cell suspensions were labeled with a monoclonal anti-LFA-1 antibody (clone TS22.1, bold curve) or an isotype-matched irrelevant commercial control antibody (thin curve), followed by a phycoerythrin-conjugated goat anti-mouse IgG antibody. (B and C) Human tonsillar tissues cultured ex vivo were inoculated with standardized amounts of T-tropic (i.e., HXB) or macrophage-tropic (i.e., Ada-M) luciferase reporter virus stocks (2.5 ng of p24) either bearing or not bearing host ICAM-1. Cells mechanically isolated from control and infected tissue explants were lysed 72 h after virus inoculation, and virus-encoded luciferase activity was monitored by using a microplate luminometer. Results shown are the means ± the standard deviation (SD) of two tissue blocks from the same donor in four separate wells (i.e., eight tissue blocks) and are representative of experiments conducted with human tonsillar tissue from three different donors.

FIG. 2.

Infectivity of replication-competent virus differing in envelope determinants for human lymphoid tissue is still enhanced by the acquisition of host ICAM-1 protein. Tonsillar tissue explants were infected with similar amounts of fully competent isogenic ICAM-1/NEG (open columns) and ICAM-1/POS (solid columns) HIV-1 particles bearing a distinct tropism and were analyzed for p24 concentration in the culture medium at the times indicated. Presented are the mean values ± the SD of two tissue blocks from the same donor in four separate wells (i.e., eight tissue blocks). These data are representative of experiments conducted with human tonsillar tissue from four different donors.

FIG. 3.

ICAM-1-LFA-1 interaction is responsible for the noticed increase in HIV-1 infectivity for histocultures of human lymphoid tissue that is conferred by cellular ICAM-1. Isogenic luciferase reporter ICAM-1/NEG and ICAM-1/POS viruses (panel A, T-tropic; panel C, M-tropic) were pretreated with an anti-ICAM-1 blocking antibody (i.e., RR1/1.1.1) before inoculation of human lymphoid tissue. In some instances, histocultures of human lymphoid tissue were pretreated with an anti-LFA-1 blocking antibody (i.e., TS1/22.1) prior to infection with reporter ICAM-1/NEG and ICAM-1/POS viruses (panel B, T-tropic; panel C, M-tropic). After 72 h, cells were mechanically isolated from control or infected tissue blocks, and infection was evaluated by measuring luciferase activity in the lysates. The results shown are the mean values ± the SD of two tissue blocks from the same donor in four separate wells (i.e., eight tissue blocks) and are representative of experiments with tissue from three donors.

FIG. 4.

Expression of an activated LFA-1 conformational state in human tonsillar tissue explants further augment infectivity of ICAM-1-bearing HIV-1 particles. Human lymphoid tissues cultured ex vivo were either left untreated or treated with an anti-CD3 antibody (i.e., OKT3) prior to infection with isogenic recombinant luciferase-encoding ICAM-1/NEG and ICAM-1/POS viruses (panel A, T-tropic; panel B, M-tropic). After 72 h, the cells were mechanically isolated from control or infected tissue blocks, and infection was evaluated by measuring the luciferase activity in the lysates. The results shown are the mean values ± the SD of two tissue blocks from the same donor in four separate wells (i.e., eight tissue blocks) and are representative of experiments with tissue from three donors. Data are expressed as the fold induction relative to the basal luciferase activity in uninfected control cells.

FIG. 5.

Incorporation of foreign ICAM-1 protein in X4 HIV-1 variant results in a more dramatic depletion of CD4⁺ T cells in human lymphoid tissues. Histocultures of human tonsils were inoculated with similar concentrations of isogenic X4 (NL4-3) and R5 (JR-CSF) virions bearing or not on their surface host-derived ICAM-1. (A) Kinetics of viral p24 production is shown for ICAM-1/NEG NL4-3 and JR-CSF virions. (B) Tonsil explants were mechanically disrupted at 10 days after virus infection to obtain cell suspensions. Next, the cells were stained with the Tritest kit that allows measurements by flow cytometry of both CD4⁺ and CD8⁺ T lymphocytes. The numbers represent the frequency of events in each quadrant. (C) The ratio of CD4⁺ to CD8⁺ T cells as a percentage of the uninfected control cells from the same donor is indicated at the top of each bar for each virus preparation used. The results are given as pooled data on two tissue blocks from the same donor in four separate wells (i.e., eight tissue blocks) and are representative of experiments with tissue from three donors.

FIG. 6.

Replication of X4 and R5 clinical HIV-1 isolates in human lymphoid tissue is reduced by a single pretreatment with a blocking anti-ICAM-1 antibody. Two primary isolates of HIV-1 that were expanded in human mononuclear cells were initially pretreated either with the anti-ICAM-1 RR1/1.1.1 blocking antibody or with an isotype-matched irrelevant control antibody. Next, the replication kinetics of such treated virus preparations in human lymphoid tissues was assessed by p24 measurements. The results shown are the mean values ± the SD of two tissue blocks from the same donor in four separate wells (i.e., eight tissue blocks) and are representative of experiments with tissue from three donors.

FIG. 7.

T-tropic and M-tropic isolates of HIV-1 incorporate functionally relevant levels of cellular ICAM-1 when produced in histocultures of human tonsils. (A) Mechanically disrupted single-cell suspensions from tissue blocks were stained with a monoclonal anti-ICAM-1 antibody (clone RR1/1.1.1), followed by treatment with a phycoerythrin-conjugated goat anti-mouse IgG antibody. (B) The indicated virus preparations (2.5 ng of p24) were subjected to a capture virus assay by using magnetic beads coated with either an anti-ICAM-1 (clone RR1/1.1.1) or an isotype-matched anti-CD45RO antibody (clone UCHL-1). The amount of virus captured by each antibody was estimated with the use of a virus p24 antigen capture assay. Magnetic beads coated with the anti-CD45RO antibody served as controls to determine background levels of captured viruses. The data shown represent the ratio of captured virions with antibody reactive with human ICAM-1 and CD45RO, respectively.