The integrin alpha4beta7 forms a complex with cell-surface CD4 and defines a T-cell subset that is highly susceptible to infection by HIV-1

Abstract

Both activated and resting CD4(+) T cells in mucosal tissues play important roles in the earliest phases of infection after sexual transmission of HIV-1, a process that is inefficient. HIV-1 gp120 binds to integrin alpha(4)beta(7) (alpha(4)beta(7)), the gut mucosal homing receptor. We find that alpha(4)beta(7)(high) CD4(+) T cells are more susceptible to productive infection than are alpha(4)beta(7)(low-neg) CD4(+) T cells in part because this cellular subset is enriched with metabolically active CD4(+) T cells. alpha(4)beta(7)(high) CD4(+) T cells are CCR5(high) and CXCR4(low); on these cells, alpha(4)beta(7) appears in a complex with CD4. The specific affinity of gp120 for alpha(4)beta(7) provides a mechanism for HIV-1 to target activated cells that are critical for efficient virus propagation and dissemination following sexual transmission.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

α4β7high CD4+ T cells are a preferential target of productive infection. In vitro infection of CD4+ T cells after 6 days of culture in the presence of retinoic acid. (A) Flow cytometric analysis of cell surface integrin β7 and intracellular Gag p24 expression on and in CD4+ T cells 3, 6, and 8 days after inoculation with the R5 HIV-1 SF162. (B) Percent intracellular Gag p24 expression in α4β7high and α4β7low-neg CD4+ T cells 3 days post-inoculation using three different amounts of SF162. Values represent the % p24+ cells within each subset. (C) Comparison of integrin β7 expression on CD4+ T cells 8 days post-inoculation with the same cells left uninfected. (D) p24 antigen ELISA of culture supernatants harvested from α4β7high and α4β7low-neg CD4+ T-cell subsets 3, 6, and 8 days post-inoculation with SF162. Levels of integrin β7 expression on both subsets on the day of inoculation are included (Inset). These results are representative of three independent experiments using different donor CD4+ T cells.

Fig. 2.

α4β7high CD4+ T cells express high levels of CCR5 and are metabolically active. Flow cytometric analysis of peripheral CD4+ T cells cultured in retinoic acid for 6 days followed by staining with fluoresceinated mAbs specific for (A) β7 and CD45RO. (B) β7 and CCR5. (C) β7 and Ki-67. This is a representative analysis of receptor expression on more than three independent donor CD4+ T cells.

Fig. 3.

Activated CD4+ T cells in the gut and rectum are enriched in the α4β7high subset. Cells freshly isolated from rectal and colon biopsies were analyzed by flow cytometry. (A) A representative analysis of CCR5 and Ki-67 expression on β7high and β7low-negCD4+ T cells. (B) Summary of Ki-67 and CCR5 expression on β7high and β7low-negCD4+ T cells isolated from the colon and rectum of three healthy donors. Values are reported as % within each population. Average % expression of CCR5 and Ki-67 expression in all β7high and β7low-negCD4+ T-cell samples analyzed is presented along with a significance value (nonparametric Wilcoxon signed-rank test for paired samples). (C) α4β7+/CD4+ T cells are detected in female genital mucosa (Mean 17.5, S.D. 13.4).

Fig. 4.

Delay in HIV-1 replication by an α4 mAb. (A–C) Purified CD4+ T cells cultured in retinoic acid and inoculated with a low amount of HIV-1 SF162 in the presence of IgG1 or the α4 mAb 2B4 (as indicated). Viral replication was determined by measuring by p24 Gag levels in culture supernatants on days 3, 6, and 9 post-infection. Three representative replication time-courses are presented. (D) Cumulative inhibition of viral replication (percent reduction in p24 Gag) from six independent infections mediated by mAb 2B4 relative to an IgG1 control on days 6 and 9 is presented. 2B4 significantly inhibited viral replication on day 6 (P < 0.001), but not on day 9 (P < 0.139). On average there is an 80% (95% CI: 71–89%) reduction in the level of p24 on day 6 in the infection in presence of 2B4. Error bars represent standard deviation from mean inhibition. Inhibition on day 6 was significantly greater than on day 9 (Wilcoxon signed-rank test).

Fig. 5.

On gut α4β7high CD4+ T cells α4β7 colocalizes with CD4 and CCR5. Freshly isolated gut cells obtained from biopsies taken from healthy donors were stained with the α4β7 mAb Act-1 (red), the CD4 mAb OKT4 (purple), and the CCR5 mAb 2D7 (green) and viewed under a confocal microscope. Unstained and individual stains of a representative cell are presented along with digitally defined regions of colocalization between α4β7 and CD4 (yellow) and α4β7, CD4 and CCR5 (blue). This cell is representative of greater that 60 cells analyzed from four donors.

Fig. 6.

Integrin β7 coprecipitates with the CD4 receptor. (A) A Western blot stained with a an integrin β7 polyclonal antisera of cell lysates derived from α4β7high CD4+ T cells treated or not with the crosslinking reagent DTSSP followed by coprecipitation with protein A agarose beads and the CD4 mAb OKT4 (lane 1), IgG1+DTSSP (lane 2), and OKT4+DTSSP (lane 3). A recombinant soluble α4β7 was run directly as a positive control (lane 4). These results are representative of three independent experiments. (B) A schematic depicting approximate sizes of α4β7, CD4, and a gp120 trimer.