Lysophosphatidylcholine Acyltransferase 2 Contributes to Increased Allergic and Irritant Inflammation in Mice

Platelet-activating factor (PAF) is an important chemical mediator in the field of inflammation, but its function in the skin is unclear. To unravel the role of PAF, we focused on lysophosphatidylcholine acyltransferase 2 (LPCAT2 also called LPLAT9), a biosynthetic enzyme involved in PAF production, and investigated the role of PAF in allergic contact dermatitis (ACD) and irritant contact dermatitis (ICD). We measured the amount of PAF in the skin and investigated the ear swelling responses and leukocyte infiltration into the skin following the application of 2,4,6-trinitro-1-chlorobenzene (TNCB) or croton oil in wild-type (WT) and LPCAT2 knockout (LPCAT2-KO) mice. The amount of PAF was increased in the skin of WT mice after TNCB or croton oil application but not detected in LPCAT2-KO mice. The ear swelling response was decreased in LPCAT2-KO mice compared with that in WT mice. In the ACD model, the numbers of lymphocytes, eosinophils, macrophages, mast cells and neutrophils were smaller in LPCAT2-KO mice than in WT mice. In the ICD model, the ear swelling response was also decreased in LPCAT2-KO mice compared with that in WT mice. When double staining of each inflammatory cell type and LPCAT2 was performed in ACD tissue, marked co-staining of the eosinophil marker and LPCAT2 was observed. In addition, LPCAT2 expression was observed in the epidermis. These results indicate that PAF is involved in the infiltration of several cell types into the sites of allergic and non-allergic skin inflammation. Furthermore, eosinophils and keratinocytes are primarily responsible for PAF production in skin inflammation.