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The Regulatory Role of the Oral Commensal Streptococcus mitis on Human Monocytes
Author(s) -
Engen S. A.,
Schreurs O.,
Petersen F.,
Blix I. J. S.,
Bækkevold E. S.,
Schenck K.
Publication year - 2018
Publication title -
scandinavian journal of immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.934
H-Index - 88
eISSN - 1365-3083
pISSN - 0300-9475
DOI - 10.1111/sji.12636
Subject(s) - streptococcus mitis , immune system , biology , microbiology and biotechnology , chemokine , secretion , immunology , transcriptome , ccl2 , interleukin 8 , gene expression , inflammation , streptococcus , gene , bacteria , genetics , biochemistry
Streptococcus mitis colonizes all niches of the human oral cavity from early infancy and throughout life. Monocytes patrol blood vessels, lymphoid and non‐lymphoid tissues and migrate into infected tissue where they participate in the inflammatory cascade and immune regulation. Here, we studied the effect of S. mitis on monocytes. Transcriptome analysis of monocytes exposed to S. mitis (SmMo) revealed increased transcription of chemotactic factors ( CCL 2, CCL 3, CCL 20, CXCL 1, CXCL 2 ) and cytokines ( IL 1A, IL 1B, IL 6, IL 23, IL 36G, TNF ), indicating that S. mitis may trigger recruitment of leucocytes and initiate inflammation. Increased transcription in SmMo of IL 1B, IL 6 and IL 23 indicated that S. mitis may participate in the induction of Th17 responses and agreed with our earlier findings of S. mitis ‐mediated memory Th17 reactivity. Furthermore, S. mitis inhibited tetanus toxoid‐specific CD 4 T cell proliferation. This can be due to the increased secretion of IL ‐10 and expression of PD ‐L1 that was observed in SmMo. PGE 2 can modulate IL ‐10 and PD ‐L1 expression, concomitant with that of CCR 7, IL ‐12 and IL ‐23 that also were changed. This, along with increased SmMo transcription of PTGS 2 ( COX 2) and PTGER 4 ( EP 4), pointed to a role of PGE 2. Measurement of PGE 2 secretion by SmMo showed indeed a marked increase, and chemical inhibition of PGE 2 production lowered the PD ‐L1 expression on SmMo. In conclusion, our findings show that S. mitis may trigger immune modulation by recruiting immune cells to the site of infection, while at the same time dampening the severity of the response through expression of IL ‐10, PGE 2 and PD ‐L1.