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.


RESULTS
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
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.
Morandi
Fabio
F
Laboratory of Oncology, G. Gaslini Children's Hospital, Genoa, Italy. fabiomorandi@ospedale-gaslini.ge.it
Ferretti
Elisa
E
Bocca
Paola
P
Prigione
Ignazia
I
Raffaghello
Lizzia
L
Pistoia
Vito
V
D015153:Blotting, Western; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects* / Q000378:metabolism*; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects* / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D002633:Chemotaxis / Q000187:drug effects*; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D006680:HLA Antigens / Q000494:pharmacology*; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000494:pharmacology*; D006801:Humans; D007150:Immunohistochemistry; D056747:Immunomodulation / Q000187:drug effects / Q000276:immunology; D066298:In Vitro Techniques; D014066:Palatine Tonsil / Q000166:cytology; D010766:Phosphorylation / Q000187:drug effects; D054390:Receptors, CCR2 / Q000378:metabolism; D054367:Receptors, CXCR3 / Q000378:metabolism; D019718:Receptors, CXCR4 / Q000378:metabolism; D054380:Receptors, CXCR5 / Q000378:metabolism; D019707:Receptors, Chemokine / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
C515334:CCR2 protein, human; C515187:CXCR3 protein, human; C527276:CXCR4 protein, human; C095085:CXCR5 protein, human; D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D054390:Receptors, CCR2; D054367:Receptors, CXCR3; D019718:Receptors, CXCR4; D054380:Receptors, CXCR5; D019707:Receptors, Chemokine