Chitin oligomers directly promote lymphoid innate and adaptive immune cell activation

Background: Chitin is a highly abundant N-acetyl-glucosamine (GlcNAc) polysaccharide which has been linked to immune responses in the context of fungal infections and allergic asthma, especially T helper 2 (Th2) immune responses. Unfortunately, due to the frequent use of crude chitin preparations of unknown purity and degree of polymerization there is still great uncertainty how chitin activates different parts of the human immune system. Objective: We recently identified chitin oligomers of six GlcNAc units as the smallest immunologically active chitin motif and the innate immune receptor TLR2 as primary chitin sensor on human and murine myeloid cells, but the response of lymphoid cells to oligomeric chitin has not been investigated and was addressed here. Methods: Flow cytometric analysis of primary human immune cells upon stimulation with oligomeric chitin. Results: Here we report that chitin oligomers also activate immune responses by both primary lymphoid innate and adaptive immune cells: Notably, chitin oligomers activated Natural Killer (NK) cells and B lymphocytes. Moreover, the maturation of dendritic cells enabled CD8 T cell recall responses. Conclusions: Our results suggest that chitin oligomers not only trigger immediate innate responses in limited range of myeloid cells but exert critical activities across the entire human immune system. ### Competing Interest Statement KF, YCG, CG and/or AW were listed as inventors on two German patents, which have been discontinued since 2020. None of the other authors declares a conflict of interest. There are no further conflicts of interest to declare.