Fig. 3.

Involvement of the skin microbiota in rosacea pathophysiology. Pattern recognition receptors (PRRs) expressed on the skin participate in a continuous immune surveillance that allows symbiont microorganisms to thrive while eliminating potential pathogens. Two of these PRRs—TLR-2 and NLRP3 (also called NALP3)—are upregulated in rosacea patients, and their activation by Demodex mites is thought to trigger inflammation in rosacea. Microbiota residing on Demodex mites may also be involved in this process: antigens from Bacillus oleronius reportedly induced the proliferation of peripheral blood mononuclear cells from rosacea patients and stimulated the production of cathelicidin, MMP-9, TNF, and IL-8 by neutrophils from healthy subjects. AMP anti-microbial peptide, Cox cyclooxygenase, IL interleukin, KLK kallikrein, LL-37 active peptide form of cathelicidin, MMP matrix metalloproteinase, NALP Nacht leucine-rich repeat protein, NLRP nucleotide-binding oligomerization domain (NOD)-like receptor family, pyrin domain-containing, PAR protease-activated receptor, TLR toll-like receptor, TNF tumor necrosis factor, VEGF vascular endothelial growth factor