Superantigen activation of CD4+ and CD8+T cells from HIV-infected subjects: role of costimulatory molecules and antigen-presenting cells (APC)

Abstract

T cell receptor (TCR) triggering via superantigens induces decreased proliferative responses and increased apoptosis in T cells from HIV-infected patients compared with controls. Our aim was to delineate the role of intrinsic T cell defects, of APC dysfunction and of cytokines and costimulatory signal dysregulation in the deficient responses of CD4+ and CD8+ T cells from HIV+ subjects to the superantigen Staphylococcus enterotoxin A (SEA). Proliferation and IL-2R alpha up-regulation on SEA-stimulated CD4+ and CD8+ T cells in whole blood were reduced in HIV+ subjects with CD4 counts < 500, compared with controls. Neither addition of IL-2, IL-12 or phorbol myristate acetate (PMA) nor neutralization of endogenous IL-10, tumour necrosis factor-alpha (TNF-alpha), TNF-beta or transforming growth factor-beta (TGF-beta) could restore the decreased activation by SEA. Possible intrinsic T cell defects were studied by presenting SEA on HLA-DR-transfected Chinese hamster ovary (CHO) cells, co-expressing LFA3 and/or CD80, to purified T cells. In this system CD8+ T cells from most HIV+ patients were hyporesponsive with regard to IL-2 production, IL-2R alpha up-regulation and proliferation, whereas clearly reduced responses were only shown in CD4+ T cells from AIDS patients. Similarly, apoptosis was increased in CD8+ T cells from all patients, but only in CD4+ T cells from AIDS patients. During HIV infection, the responses to TCR triggering through SEA are deficient in both T cell subsets. The intrinsic defect appears earlier during disease progression in purified CD8+ T than in CD4+ T cells, it occurs in conjunction with both CD2 and CD28 costimulation, and it is correlated with increased levels of apoptosis.

Fig. 1

Proliferative responses (a) and percentage of CD25⁺CD4⁺ (b) or CD8⁺ T cells (c) after stimulation of whole blood with Staphylococcal enterotoxin A (SEA) (100 and 10ng/ml). Flow cytometric analysis of CD25 expression was performed on day 4. HIV⁻ controls (□, n = 46) were compared with HIV⁺ subjects grouped according to their CD4 counts: group 1, CD4 counts > 500 (▪, n = 11); group 2, CD4 counts between 200 and 500 (, n = 20) and group 3, CD4 counts < 200 (, n = 17). Median ± confidence interval (CI) are given. Significant differences between patients and controls are indicated: *P < 0.05; **P < 0.01; ***P < 0.002; ****P < 0.0005. NS, Not significant.

Fig. 2

Expression of CD25 on CD4⁺ (a) or CD8⁺ T cells (b) from HIV⁻ controls (○) and HIV⁺ subjects (•). Whole blood was cultured with Staphylococcal enterotoxin A (SEA) alone (10 ng/ml) or with SEA (10 ng/ml) plus phorbol myristate acetate (PMA; 1 ng/ml). Paired sample analysis revealed significant differences between SEA and SEA plus PMA in both T cell subsets from both patients and controls (P<0.0001). Significant differences between patients and controls are indicated: *P<0.05; ***P<0.002; ****P<0.0005.

Fig. 3

Proliferative responses of purified CD4⁺ (a) or CD8⁺ (b) T cells after a 4-day stimulation with Staphylococcal enterotoxin A (SEA; 0.1 ng/ml) in the absence or presence of various Chinese hamster ovary (CHO) cell lines. Individual data are presented for seven (a) or 11 (b) HIV⁻ subjects (○), seven HIV⁺ subjects with CD4 counts > 200 (▿) and three HIV⁺ subjects with CD4 counts < 200 (▴). The median proliferative response for patients or controls is indicated with a horizontal line.

Fig. 4

Apoptosis and CD25 expression in CD4⁺ (a,c) and CD8⁺ T cells (b,d) from six HIV⁻ controls (○) and 10 HIV⁺ subjects (▴). (a,b) Data obtained in peripheral blood mononuclear cell (PBMC) cultures. (c,d) Data from purified T cell cultures. The patients were divided into two groups: CD4 counts >200 (▿) and CD4 counts <200 (▴). The percentage of apoptotic T cells was defined by FCS-SSC analysis. Significant differences between the different stimuli are indicated: *P<0.05; **P<0.01; ***P<0.002.