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Osteopontin deficiency affects imiquimod‐induced psoriasis‐like murine skin inflammation and lymphocyte distribution in skin, draining lymph nodes and spleen

Osteopontin (OPN) that enhances autoimmunity is expressed in psoriasis lesions; however, its functions in psoriatic inflammation are unknown. We investigated the role of OPN in OPN deficient mice (OPN−/−) by inducing psoriasis‐like inflammation through skin application of imiquimod (IMQ). OPN−/− mice treated with IMQ showed delayed onset ear swelling and attracted less inflammatory cells to the skin. IMQ‐induced lymph node swelling was reduced in the absence of OPN, and IMQ‐mediated expansion of B cells was inhibited. Further, reduction of CD4+ T‐cell numbers by IMQ in lymph nodes was suppressed in OPN−/− mice, with an increase in the CD4/CD8 ratio. A comparable pattern was found in spleen. Importantly, IMQ‐induced IL‐17 and IL‐4 expression by CD4+ lymph node T cells was reduced in OPN−/− mice. In conclusion, OPN may modulate psoriasis‐like inflammation through altering lymphocyte distribution in skin and draining lymph nodes and by inducing IL‐17 expression of inflammatory T cells.