METEORIN-LIKE is a cytokine associated with barrier tissues and alternatively activated macrophages

•Meteorin-like (Metrnl) is a small (28KDa) secreted protein.•Metrnl is expressed by barrier tissues (skin, mucosa) and M2 macrophages.•Metrnl is over-expressed in several human skin inflammatory diseases.•Metrnl is over-expressed in rheumatoid arthritis lesions.•Metrnl is a cytokine involved in innate immunity as well as inflammation.

Cytokines are involved in many functions of the immune system including initiating, amplifying and resolving immune responses. Through bioinformatics analyses of a comprehensive database of gene expression (BIGE: Body Index of Gene Expression) we observed that a small secreted protein encoded by a poorly characterized gene called meteorin-like (METRNL), is highly expressed in mucosal tissues, skin and activated macrophages. Further studies indicate that Metrnl is produced by Alternatively Activated Macrophages (AAM) and M-CSF cultured bone marrow macrophages (M2-like macrophages). In the skin, METRNL is expressed by resting fibroblasts and IFNγ-treated keratinocytes. A screen of human skin-associated diseases showed significant over-expression of METRNL in psoriasis, prurigo nodularis, actinic keratosis and atopic dermatitis. METRNL is also up-regulated in synovial membranes of human rheumatoid arthritis. Taken together, these results indicate that Metrnl represents a novel cytokine, which is likely involved in both innate and acquired immune responses.