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Phongsisay, V;Iizasa, E;Hara, H;Yoshida, H;
Activation of the innate immunity by adjuvants, such as pertussis toxin (PTX), in the presence of autoreactive lymphocytes and antigen mimicry is sufficient to trigger autoimmunity. Toll-like, C-type lectin, and immunglobulin-like receptors play an important role in the innate immunity by sensing a variety of microbial products through several adaptor proteins, including MyD88, DAP12, and FcR. This study investigated the interaction between PTX and innate immune components. The direct interactions between coated PTX and receptor-fusion proteins were examined using ELISA-based binding assays. Functionally, PTX-binding receptors could be classified into two groups: inhibition (DAP12-coupled TREM2, ITIM-bearing SIRP, SIGNR1/SIGNR3/DCSIGN) and activation (MyD88-associated TLR4, DAP12-coupled LMIR5/CD300b, FcR-coupled LMIR8/CD300c, CLEC9A, MGL-1). DAP12, MyD88, and FcR were selected for further investigation. A comprehensive analysis of gene transcription showed that PTX up-regulated the expression of various inflammatory mediators. DAP12 deficiency resulted in reduction or enhancement of inflammatory responses in a cytokine-specific manner. PTX was able to activate the TREM2-DAP12 signalling pathway. PTX induced lower expression of inflammatory mediators in the absence of FcR alone and substantially lost its inflammatory capacity in the absence of both FcR and MyD88. PTX was able to activate the MyD88-NF-B signalling pathway in the presence of TLR2 or TLR4. The inflammatory activity of PTX was completely lost by heating. These results demonstrate that PTX targets the innate immunity through DAP12, FcR, and MyD88 providing new insights into the immunobiology of PTX.