Mmm-derived lipid-associated membrane proteins activate IL-1β production through the NF-κB pathway via TLR2, MyD88, and IRAK4

Mycoplasma mycoides subsp.mycoides (Mmm) is a pathogen that causes pneumonia, otitis media, and arthritis in young calves. Its pathogenesis is attributed in part to excessive immune responses. Mmm-derived lipid-associated membrane proteins (LAMPs) are potent inducers of the host innate immune system; however, interactions between Mmm-derived LAMPs as pathogenic agents, toll-like receptors (TLRs), and the signaling pathways responsible for activating inflammation and nuclear factor (NF)-κB have not been fully elucidated. Here, we analyzed the expression kinetics of interleukin (IL)-1β in Mmm-derived LAMP-stimulated embryonic bovine lung (EBL) cells and found that Mmm-derived LAMPs induced IL-1β expression. Subcellular localization analysis revealed the nuclear translocation of the NF-κB p65 subunit after EBL cells were stimulated with Mmm-derived LAMPs. Furthermore, a specific inhibitor assay demonstrated that NF-κB is required for Mmm-derived LAMP-induced IL-1β expression. Additionally, overexpression of TLR2, myeloid differentiation primary response gene 88 (MyD88), and IL-1 receptor-associated kinase 4 (IRAK4) increased IL-1β expression during LAMP stimulation, and TLR2-neutralizing antibodies reduced IL-1β expression in EBL cells during LAMP stimulation. Furthermore, LAMPs inhibited IL-1β expression following transfection with dominant-negative MyD88 and IRAK4 variants. These results suggested that Mmm-derived LAMPs activate IL-1β production through the NF-κB pathway via TLR2, MyD88, and IRAK4.