Hair follicles harbour sentinel cells for immune surveillance

Photo by OpenStax College via Wikimedia Commons

Researchers at the University of California, Riverside School of Medicine have identified previously unrecognized immune surveillance structures within hair follicles that may fundamentally change the concept of cutaneous barrier defence. The murine study, published in Frontiers in Cell and Developmental Biology, reveals M cell-like sentinel cells in hair follicle epithelium that appear to monitor environmental microbial exposure and mount localized immune responses, particularly against Gram-positive bacteria.

In a press release, senior author and professor of biomedical sciences Dr. David Lo noted that gut and airway epithelia use single-cell layers for direct environmental sampling. The study findings, he said, “… raise a long-standing question in immunology: How does the skin efficiently monitor external threats despite its thickness?”

Dr. Lo's team proposes that hair follicles function as localized “gateway” structures concentrating both environmental material and immune sensing activity. Within these niches, M cell-like sentinel cells participate in immune responses, with PGRP-S expression in flank skin hair follicle epithelium showing transient induction upon exposure to Staphylococcus aureus suspensions.

First author Diana Del Castillo noted that “Hair follicles may represent a central hub for immune surveillance in the skin. These structures bring together environmental exposure, immune sensing, and potentially even neural signalling in a highly localized environment.”

The identified structures localize to regions closely associated with nerve endings, suggesting potential integration between immune detection and sensory signalling pathways.

Their future research will focus on anatomical mapping in whisker follicles due to their dense innervation, interaction patterns with surrounding neural and immune cells, and translation to human cutaneous biology. Del Castillo said: “Our study adds to growing evidence that epithelial barriers across tissues share more diverse and dynamic immune-related functions than previously recognized, particularly in their ability to respond rapidly to microbial stimuli.”