Gal-9 enhances HIV-1 infection of resting CD4⁺ T cells. (A) Percentages of CD4⁺p24⁺ in nonactivated CD4⁺ T cells in the absence or presence of Gal-9 (0.5 μg/mL or 1 μg/mL) 2 hours before HIV-1 infection with X-4-tropic (HIV-1_LAI) isolates. Bounds of boxes denote interquartile range; lines within boxes denote median; and whiskers indicate range. Significance was tested using Kruskal-Wallis test. (B) Representative flow cytometry dot plots from CD4⁺ T cells stimulated with 0.5 μg/mL or 1 μg/mL Gal-9 before infection with X-4-tropic HIV-1 isolate in vitro. (C) Rested CD4⁺ T cells were incubated with bacitracin (+Bac), or anti-PDI mAb RL77 (1:3000 D) or in the absence of both (−PDI mAb or Bac). Then Gal-9 (0.5 μg/mL or 1 μg/mL) as indicated was added for 2 hours and cells were washed. Five days after infection, the number of infected cells with X4-tropic HIV-1 isolate was quantified by intracellular viral p24 antigen staining using flow cytometry. (D) PHA activated CD4⁺ T cells were incubated with bacitracin (+Bac), anti-PDI mAb RL77 (1:3000 D), or in the absence of both (−PDI mAb or Bac). Then Gal-9 (0.5 μg/mL or 1 μg/mL) as indicated was added for 2 hours and cells were washed. Five days after infection, the number of infected cells with X4-tropic HIV-1 isolate was quantified by intracellular viral p24 antigen staining using flow cytometry.