Immunosuppressive effect of prolactin‐induced protein: a new insight into its local and systemic role in chronic allergic contact dermatitis

Summary Background  Prolactin-induced protein (PIP) has been shown to bind to CD4 and is speculated to block CD4–HLA-DR interaction. However, the immunomodulatory effect of PIP on chronic allergic contact dermatitis (ACD) remains to be elucidated. Objectives  To define the role of PIP during the immunoresponse. Methods  Using a low-dose oxazolone-induced mouse chronic ACD model, expression of PIP was examined immunohistologically. Furthermore, effects of continued exposure to a peptide mimicking the major binding site of PIP (amino acids 106–132) for CD4 was examined in a mouse chronic ACD model. Results  We clarified that keratinocytes, dermal infiltrating cells and spleen infiltrating mononuclear cells are positively stained with anti-PIP antibody. The PIP peptide significantly downregulated oxazolone-induced mouse ACD compared with controls. We also found that inflammation of the control ear, to which the PIP peptide had not been applied, was also suppressed in a synchronized manner in the late phase of ACD. Conclusions  These findings suggest that PIP might have a local and systemic immunosuppressive effect in mouse chronic ACD.