A Novel Mechanism of Soluble HLA-G Mediated Immune Modulation: Downregulation of T Cell Chemokine Receptor Expression and Impairment of Chemotaxis

BACKGROUND: In recent years, many immunoregulatory functions have been ascribed to soluble HLA-G (sHLA-G). Since chemotaxis is crucial for an efficient immune response, we have investigated for the first time the effects of sHLA-G on chemokine receptor expression and function in different human T cell populations. METHODOLOGY/PRINCIPAL FINDINGS: T cell populations isolated from peripheral blood were stimulated in the presence or absence of sHLA-G. Chemokine receptors expression was evaluated by flow cytometry. sHLA-G downregulated expression of i) CCR2, CXCR3 and CXCR5 in CD4(+) T cells, ii) CXCR3 in CD8(+) T cells, iii) CXCR3 in Th1 clones iv) CXCR3 in TCR Vdelta2gamma9 T cells, and upregulated CXCR4 expression in TCR Vdelta2gamma9 T cells. sHLA-G inhibited in vitro chemotaxis of i) CD4(+) T cells towards CCL2, CCL8, CXCL10 and CXCL11, ii) CD8(+) T cells towards CXCL10 and CXCL11, iii) Th1 clones towards CXCL10, and iv) TCR Vdelta2gamma9 T cells towards CXCL10 and CXCL11. Downregulation of CXCR3 expression on CD4+ T cells by sHLA-G was partially reverted by adding a blocking antibody against ILT2/CD85j, a receptor for sHLA-G, suggesting that sHLA-G downregulated chemokine receptor expression mainly through the interaction with ILT2/CD85j. Follicular helper T cells (T(FH)) were isolated from human tonsils and stimulated as described above. sHLA-G impaired CXCR5 expression in T(FH) and chemotaxis of the latter cells towards CXCL13. Moreover, sHLA-G expression was detected in tonsils by immunohistochemistry, suggesting a role of sHLA-G in local control of T(FH) cell chemotaxis. Intracellular pathways were investigated by Western Blot analysis on total extracts from CD4+ T cells. Phosphorylation of Stat5, p70 s6k, beta-arrestin and SHP2 was modulated by sHLA-G treatment. CONCLUSIONS/SIGNIFICANCE: Our data demonstrated that sHLA-G impairs expression and functionality of different chemokine receptors in T cells. These findings delineate a novel mechanism whereby sHLA-G modulates T cell recruitment in physiological and pathological conditions

Keratinocytes Determine Th1 Immunity during Early Experimental Leishmaniasis

Experimental leishmaniasis is an excellent model system for analyzing Th1/Th2 differentiation. Resistance to Leishmania (L.) major depends on the development of a L. major specific Th1 response, while Th2 differentiation results in susceptibility. There is growing evidence that the microenvironment of the early affected tissue delivers the initial triggers for Th-cell differentiation. To analyze this we studied differential gene expression in infected skin of resistant and susceptible mice 16h after parasite inoculation. Employing microarray technology, bioinformatics, laser-microdissection and in-situ-hybridization we found that the epidermis was the major source of immunomodulatory mediators. This epidermal gene induction was significantly stronger in resistant mice especially for several genes known to promote Th1 differentiation (IL-12, IL-1β, osteopontin, IL-4) and for IL-6. Expression of these cytokines was temporally restricted to the crucial time of Th1/2 differentiation. Moreover, we revealed a stronger epidermal up-regulation of IL-6 in the epidermis of resistant mice. Accordingly, early local neutralization of IL-4 in resistant mice resulted in a Th2 switch and mice with a selective IL-6 deficiency in non-hematopoietic cells showed a Th2 switch and dramatic deterioration of disease. Thus, our data indicate for the first time that epidermal cytokine expression is a decisive factor in the generation of protective Th1 immunity and contributes to the outcome of infection with this important human pathogen

Identification of Baicalin as an Immunoregulatory Compound by Controlling TH17 Cell Differentiation

TH17 cells have been implicated in a growing list of inflammatory disorders. Antagonism of TH17 cells can be used for the treatment of inflammatory injury. Currently, very little is known about the natural compound controlling the differentiation of TH17 cells. Here, we showed that Baicalin, a compound isolated from a Chinese herb, inhibited TH17 cell differentiation both in vitro and in vivo. Baicalin might inhibit newly generated TH17 cells via reducing RORγt expression, and together with up-regulating Foxp3 expression to suppress RORγt-mediated IL-17 expression in established TH17 cells. In vivo treatment with Baicalin could inhibit TH17 cell differentiation, restrain TH17 cells infiltration into kidney, and protect MRL/lpr mice against nephritis. Our findings not only demonstrate that Baicalin could control TH17 cell differentiation but also suggest that Baicalin might be a promising therapeutic agent for the treatment of TH17 cells-mediated inflammatory diseases