T cell activation, apoptosis and cytokine dysregulation in the (co)pathogenesis of HIV and pulmonary tuberculosis (TB)

Abstract

Immune parameters were compared in four groups of Ugandan subjects: HIV-and HIV+ adult patients with active pulmonary TB (HIV- PTB n = 38; HIV+ PTB n = 28), patients with HIV infection only (n = 26) and PPD+ healthy controls (n = 25). Compared with healthy controls, CD4 and CD8 T cells from patients with HIV and/or PTB expressed more activation markers (HLA-DR, CD38); their CD8 T cells expressed more CD95 (pre-apoptosis) and less CD28 (co-stimulatory receptor). Peripheral blood mononuclear cells (PBMC) of patients with either HIV or PTB were impaired in interferon-gamma (IFN-gamma) production upon antigenic stimulation. PTB (with or without HIV) was characterized by monocytosis, granulocytosis, increased transforming growth factor-beta 1 production and PPD-induced apoptosis. In vivo CD4 T cell depletion, in vitro increased spontaneous CD4 T cell apoptosis and defects in IFN-gamma responses upon mitogenic stimulation were restricted to HIV+ subjects (with or without PTB). Overlapping and distinctive immune alterations, associated with PTB and HIV, might explain mutual unfavourable influences of both diseases.

Fig. 1

Differentiation markers on CD4 T cells (a) and on CD8 T cells (b). Whole blood from 23 HIV⁻ PPD⁺ controls (□), 36 HIV⁻ pulmonary TB (PTB)⁺ patients (hatched), 25 HIV⁺ PTB⁻ subjects (cross-hatched) and 25 HIV⁺ PTB⁺ patients (▪) was incubated with anti-CD4 FITC, anti-CD8 PerCP and one of the following PE-labelled monoclonals: isotypic control IgG1, anti-HLA-DR, anti-CD28, anti-CD38 or anti-CD95. Using the isotypic control, the threshold of positivity in PE was fixed on channel 325 and the activation marker expression was calculated as a percentage within the gated CD4, respectively, CD8 T cells. Results are given as mean ±s.e.m. within each patient group. The significance of differences between the groups was calculated using Student's t-test for independent samples, with the following levels of significance: *P < 0·05; **P < 0·01; ***P < 0·001.

Fig. 2

Apoptosis of CD4⁺ T cells after antigenic and mitogenic stimulation. Three replicate cultures of peripheral blood mononuclear cells were incubated with medium, PPD, Mycobacterium tuberculosis (MTB) and pokeweed mitogen (PWM) from 24 HIV⁻ PPD⁺ controls (□), 30 HIV⁻ PTB⁺ patients (hatched), 14 HIV⁺ PTB⁻ subjects (cross-hatched) and 16 HIV⁺ PTB⁺ (▪) patients. Apoptosis was assessed using the TUNEL test in combination with anti-CD4–PE. Results are expressed as percentage of TUNEL (+) CD4 T cells. Indicated in the figure are the statistical significant differences (paired t-test), between the non-stimulated and the stimulated cultures within each subject group.

Fig. 3

Secretion of cytokines in cultured peripheral blood mononuclear cells (PBMC). PBMC from 23 HIV⁻ PPD⁺ controls (□), 31 HIV⁻ PTB⁺ patients (hatched), 24 HIV⁺ PTB⁻ subjects (cross-hatched) and 21 HIV⁺ PTB⁺ (▪) patients, were cultured in vitro. The respective stimuli are indicated on the abscissa. (a) IFN-γ, (b) transforming growth factor-beta 1, (c) tumour necrosis factor-alpha were measured in the supernatants by ELISA and results were expressed in pg/ml. The differences in cytokine secretion between subject groups were calculated and presented as in Fig. 1.