358 Toll-like receptor 2 partially dependent phagocytosis of cutibacterium acnes: Acne-associated strains phagocytosed more than healthy-associated strains

Abstract

Pathogen phagocytosis is a fundamental process in innate immunity and important for host response to injury and infection. Some pathogenic bacteria possess structural or biochemical characteristics that allow them to resist or avoid host phagocytic and immune responses. Acne vulgaris is a multi-factorial inflammatory skin disorder with phagocytosis of Cutibacterium acnes (C. acnes) as an important part in disease pathogenesis. Previous studies have indicated Toll-like receptor 2 (TLR2) as a mediator of C. acnes-induced cytokine secretion, and other studies have observed immune cell phagocytic ability associated with TLR2 expression. In this study, we aimed to observe the effects of TLR2 functionality on C. acnes phagocytosis. Stimulation of TLR2-wild-type (WT) and TLR2-knock-out (KO) THP1 monocytes with C. acnes showed a decreased secretion of pro-inflammatory cytokines IL-1β, IL-6, IL-12p70, and TNF-α in TLR2-KO cells. Flow cytometry analysis of TLR2-WT and TLR2-KO cells stimulated with fluorescently labeled C. acnes revealed decreased phagocytosis in TLR2-KO cells. However, phagocytosis was not completely prevented in TLR2-KO cells, suggesting involvement of other co-receptors in C. acnes phagocytosis. Single-cell RNA sequencing of acne lesions showed increased expression of ITGAM, ITGB2, and C5AR1 genes of the complement system when compared to non-lesional skin, suggesting that immune cell phagocytosis of C. acnes does not completely depend on TLR2 and may involve activation of the complement system. Further analysis revealed that in both TLR2-WT and TLR2-KO cells, monocytes phagocytosed more acne-skin associated C. acnes strains (CA) than healthy-skin associated strains (CH). While both CA and CH induce similar pro-inflammatory cytokine secretion levels, CA are phagocytosed more than CH, suggesting the possibility of a structural or biochemical difference between CA and CH that may influence immune cell pathogen recognition, phagocytosis, and anti-microbial activity.