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

Abstract

BackgroundIn 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 FindingsT 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 Vδ2γ9 T cells, and upregulated CXCR4 expression in TCR Vδ2γ9 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 Vδ2γ9 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 (TFH) were isolated from human tonsils and stimulated as described above. sHLA-G impaired CXCR5 expression in TFH 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 TFH cell chemotaxis. Intracellular pathways were investigated by Western Blot analysis on total extracts from CD4+ T cells. Phosphorylation of Stat5, p70 s6k, β-arrestin and SHP2 was modulated by sHLA-G treatment.Conclusions/SignificanceOur 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.

Soluble HLA-G dampens CD94/NKG2A expression and function and differentially modulates chemotaxis and cytokine and chemokine secretion in CD56bright and CD56dim NK cells

“…We have demonstrated that sHLA-G induced p-Stat5 down-regulation both in CD56 dim and CD56 bright NK cells, leading to deregulation of the transcription of several genes. These data are in line with our previous study on T lymphocytes, in which we have demonstrated that sHLA-G down-regulated Stat5 phosphorylation through an increased phosphorylation of the protein phosphatase SHP-2, 28 and another study showing that sHLA-G downregulated JAK2, Stat3, and Stat5 phosphorylation in erythroid cells. 50 The reasons why, at variance with a previous report, 18 we did not detect any difference in p-Stat3 expression in CD56 dim or CD56 bright NK cells on treatment with sHLA-G or medium are unknown, but they may be related to the different sources of NK cells tested.…”

“…28 Here, we report that sHLA-G modulated expression and function of different chemokine receptors on CD56 bright and CD56 dim resting NK cells. Similar results were obtained using NK cells from PB and tonsil, tested as prototype of secondary lymphoid organ.…”

“…Finally, to investigate whether ILT2, a receptor for HLA-G, was involved in down-modulation of CXCR3 (as reported by Morandi et al 28 ) and NKG2A, additional experiments were performed using an anti-ILT2/CD85j blocking mAb. As shown in Figure 5B, sHLA-G-mediated inhibition of CXCR3 (top) and NKG2A (bottom) expression on NK cells was partly but significantly reverted by preincubating these cells with anti-ILT2/CD85j mAb (MRFI median: untreated [ctr], 30.65 Ϯ 10.47 and 14.67 Ϯ 0.44, respectively; sHLA-G, 5.48 Ϯ 0.53 and 7.45 Ϯ 0.2, respectively; sHLA-G ϩ anti-ILT2 mAb, 14.2 Ϯ 4.64 and 8.61 Ϯ 0.29 respectively; P ϭ .01) but not with irrelevant isotype-matched mAb, demonstrating that sHLA-G modulated CXCR3 and NKG2A expression partly through the interaction with ILT2 receptor.…”

“…In another experimental model, sHLA-G was found to boost expression of its own receptor ILT2/CD85j, 44 a finding that was not confirmed by our study and by another published study. 28 This is probably because of different cell types used as targets for sHLA-G, the different experimental settings, or both.…”

Distinctive Immunological Functions of HLA-G

“…HLA-G1 was indeed shown to promote T helper (h)2 polarization of naïve T cells (Kanai et al, 2001b;Kapasi et al, 2000) whereas HLA-G5 induces tumor necrosis factor (TNF)-, IFN-, and IL-10 ( Kanai et al, 2001a). Morandi et al recently described that HLA-G5 has an additional effect on CD4 + T cells since it down-regulates expression and function of CCR2, CXCR3, and CXCR4 on different subsets of activated CD4 + T cells, impairing their migratory capability (Morandi et al, 2010).…”