Evidence for murine cutaneous immune surveillance localized to hair follicle epithelium

Epithelial expression of the gene encoding the anti-microbial peptide PGRP-S was previously found to be specifically associated with M cells in mucosal epithelium. However, recent studies have found PGRP-S expression by a variety of epithelia not providing direct M cell-like microparticle transcytosis into lymphoid tissues. Thus, in mouse epidermis we found that PGRP-S expression, revealed by a dsRed reporter, was specific to subsets of hair follicle epithelium, depending on the specific skin region, and not associated with lymphoid aggregates. Interestingly, expression in flank skin hair follicle epithelium was also transiently inducible upon exposure to a suspension of Staphylococcus aureus. Altogether, the topology of hair follicles and location of dsRed-expressing epithelia are consistent with a model in which this PGRP-S-dsRed reporter identifies a population in hair follicles associated with surveillance of environmental exposures.