Suppressed cellular alloimmune responses in HIV-exposed seronegative female sex workers

Abstract

Particular human leucocyte antigen (HLA) polymorphisms have been associated with a reduced risk of HIV transmission. However, protective alloimmune responses expected to result from such a genetic predisposition have not been demonstrated. To this end, we analysed and compared cellular and humoral alloimmune responses in a cohort of female sex workers who remained human immunodeficiency virus (HIV)-seronegative despite more than 3 years of high-risk sexual activity (ESN FSWs) with those of low-risk HIV-seronegative female blood donors in Abidjan, Côte d'Ivoire. ESN FSWs showed significantly lower allostimulated CD69 expression and secretion of interferon-gamma, macrophage inflammatory protein (MIP)-1beta and RANTES (regulated upon activation, normal T-cell expressed and secreted) by lymphocytes than controls. In contrast, ESN FSWs showed significantly higher mitogen-stimulated CD69 expression and secretion of tumour necrosis factor-alpha and MIP-1beta than controls. Suppression of cellular alloimmune responses among ESN FSWs was associated with a higher self-reported frequency of unprotected sex. Levels of anti-HLA class I alloantibodies in plasma were not significantly different between ESN FSWs and controls. These findings indicate that frequent sexual exposure to multiple partners results in suppression rather than activation of cellular alloimmune responses. Our data support the hypothesis that suppressed cellular alloimmune responses may play a role in protection against HIV infection.

Fig. 1

Testing alternative inactivation methods for one-way MLR. (a) Percentage cell death (7-AAD staining) within T-cells after inactivation with paraformaldehyde (PFA), mitomycin C (MMC) and actinomycin D (AAD). (b) MHC class I (W6/32)() and class II (HLA-DR)(▪) expression on T-cells after inactivation with PFA, MMC and AMD. (c) CD69 membrane expression on T-cells after inactivation with PFA, MMC or AMD and stimulation with PMA/ionomycin (in the absence of brefeldin A). (d) Intracellular expression of IFN-γ () and IL-4 (▪) in T-cells after inactivation with PFA, MMC or AMD and stimulation with PMA/ionomycin (in the presence of brefeldin A). Data are representative for PBMC from two controls.

Fig. 2

Kinetics of CD69 expression in a one-way MLR. Responder PBMC were derived from one control subject, pooled stimulator PBMC were derived from 5 different control subjects not related to the responder control. (a- d) Dot plots showing analysis of CD69 expression on gated CD3⁺ T-cells after 30 h of incubation in the presence of medium alone, PHA, paraformaldehyde-inactivated and actinomycin d-inactivated pooled stimulator cells, respectively. Percentages of gated events in the four quadrants are indicated. (e) CD69 expression on T-cells after incubation with medium alone (control, □), PHA (▪), paraformaldehyde-inactivated pooled stimulator cells (PFA pool, •), and actinomycin d-inactivated pooled stimulator cells (AMD pool, ▴) over a 96 h incubation period. (f) Percentage cell death (7-AAD staining) in bulk PBMC after 96 h of incubation.

Fig. 3

Associations between cellular alloimmune responses and sexual exposure among ESN FSWs. (a) Association between allostimulated CD69 expression on memory CD4⁺ T-cells and the duration of commercial sex work among ESN FSWs. (b) Association between allostimulated MIP-1β secretion and the consistency in using condoms with regular partners. Allostimulated CD69 expression was tested with linear regression adjusting for age (variable normally distributed). Allostimulated MIP-1β secretion was tested with Mann–Whitney U-tests (variable not normally distributed). P₁, comparison between FBDs and all ESN FSWs; P₂, comparison within ESN subgroups.

Fig. 4

Plasma anti-HLA class I antibodies in ESN FSWs and FBDs. (a) Percentages of HLA class I panel reactive antibodies (% PRA) among ESN FSWs (○) and FBDs (▵). Filled symbols indicate percentages above 10% with a multiple-peak pattern in the histogram plot. Horizontal lines indicate median values. P₁, Mann–Whitney U-test; P₂, logistic regression adjusting for age. (b) Scatter plot of percentage HLA class I PRA against age among ESN FSWs (○) and FBDs (▵). Symbols as in (a).