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.