Summary Platelets are primarily involved in thrombosis and haemostasis, and they have recently been shown to have a role in innate immunity and in inflammation. We have determined the markers of innate immunity that are expressed by platelets, specifically the Toll-like receptors (TLR), originating from mixes of platelet concentrates (MPC, n = 5) between day zero and day five after blood collection. The surface membrane and intracellular expression of TLR were measured, both after and without permeabilization, using flow cytometry. We observed weak expression of TLR2, TLR4 and TLR9 on the surface of CD41 + platelets. The expression levels of TLR4 were high (59 ± 2.2%). Moreover, there was a significant expression of TLR2 (47.5 ± 4.8%), TLR4 (78.8 ± 1.3%) and TLR9 (34.2 ± 7.5%) in the cytoplasm of CD41 + platelets. The expression of the three receptors did not change significantly during the course of the 5 day observation period. The percentage of TLR expression is significantly modulated between activated versus non-activated platelets, both after and without permeabilization ( P < 0.01). Study of the expression of TLR could increase our knowledge of the level of platelet participation during an immune reaction and inflammation. In the same way as the platelet ligand/receptor pair CD40L/CD40 is, the TLR are expressed by platelets, and could serve as a link between innate and adaptive immunity.

Our results demonstrate that epithelial cells respond to factors present in semen by secreting CCL20, leading to the enhancement of LCp recruitment. These data argue in favour of the implication of epithelial cells in the heterosexual transmission of HIV.

Mucosa represents the main site of pathogen/cell interactions. The two main types of cells forming the epithelial structure [epithelial cells and Langerhans cells (LC)] coordinate the first defense responses to avoid infection. To evaluate the involvement of epithelial cells in the early steps leading to a specific adaptive immune response, we have studied the interactions between vaginal epithelial and LC through the establishment of a human vaginal epithelial mucosa. We demonstrate that normal human vaginal epithelial cells constitutively secrete the chemokine macrophage inflammatory protein 3alpha/CC chemokine ligand 20 (CCL20), known to recruit LC precursors (LCps) selectively via its cognate CC chemokine receptor 6 (CCR6). This secretion is up-regulated by the proinflammatory cytokine interleukin-1beta through the nuclear factor-kappaB pathway. Similar results were obtained with the human vaginal epithelial cell line SiHa, which displays numerous homologies with normal vaginal cells. The chemotactic activity of the secreted CCL20 was demonstrated by its ability to attract LCp CCR6+. Moreover, the use of neutralizing polyclonal antibodies directed against the CCL20 molecule abolished this migration completely, suggesting that CCL20 is the main attracting factor for LCps, which is produced by the vaginal cells. These data indicate that vaginal epithelial cells play an important role in the immunological defense by attracting immune cells to the site of epithelial/pathogen contact.

X4 and R5 HIV strains are present in the semen of men infected with HIV but R5 isolates are transmitted preferentially. The role of human epithelial cells in this selection is addressed. Three human cervical cell lines-CaSki, SiHa, and HEC1A-and normal human vaginal cells from HIV-negative donors were characterized for HIV receptor expression and incubated with X4 and R5 laboratory-adapted strains or primary isolates. The infection was assessed by detection of intracellular HIV DNA. The three cell lines were shown to express on their surface the CXCR4 and GalCer molecules, but not the CD4 and CCR5 ones. The three cell lines and normal human vaginal cells were found to be selectively permissive to X4 HIV entry; the preincubation of the cell lines with rhSDF-1 inhibited this infection. The detection of the intracellular proviral DNA in the cell lines and in normal human vaginal cells demonstrated a selective integration of X4 strains. Additional experiments showed that no extracellular RNA was detected in the supernatants of HEC1A cells infected by X4 isolates either after 18 days of culture or after incubation with PHA-stimulated PBMCs and that no transmission occurred after co-culture between infected HEC1A cells and PHA-stimulated PBMCs. These results suggest specific sequestration of X4 strains by genital epithelial cells, which could explain, at least in part, the HIV tropism selection process during sexual intercourse.

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