Activation of MyD88 signaling upon staphylococcal enterotoxin binding to MHC class II molecules

PLoS One. 2011 Jan 20;6(1):e15985. doi: 10.1371/journal.pone.0015985.


Ligands binding to Toll-like receptor (TLR), interleukin 1 receptor (IL-1R), or IFN-γR1 are known to trigger MyD88-mediated signaling, which activates pro-inflammatory cytokine responses. Recently we reported that staphylococcal enterotoxins (SEA or SEB), which bind to MHC class II molecules on APCs and cross link T cell receptors, activate MyD88- mediated pro-inflammatory cytokine responses. We also reported that MyD88(-/-) mice were resistant to SE- induced toxic shock and had reduced levels of serum cytokines. In this study, we investigated whether MHC class II- SE interaction by itself is sufficient to activate MyD88 in MHC class II(+) cells and induce downstream pro-inflammatory signaling and production of cytokines such as TNF-α and IL-1β. Here we report that human monocytes treated with SEA, SEB, or anti-MHC class II monoclonal antibodies up regulated MyD88 expression, induced activation of NF-kB, and increased expression of IL-1R1 accessory protein, TNF-α and IL-1β. MyD88 immunoprecipitated from cell extracts after SEB stimulation showed a greater proportion of MyD88 phosphorylation compared to unstimulated cells indicating that MyD88 was a component of intracellular signaling. MyD88 downstream proteins such as IRAK4 and TRAF6 were also up regulated in monocytes after SEB stimulation. In addition to monocytes, primary B cells up regulated MyD88 in response to SEA or SEB stimulation. Importantly, in contrast to primary B cells, MHC class II deficient T2 cells had no change of MyD88 after SEA or SEB stimulation, whereas MHC class II-independent activation of MyD88 was elicited by CpG or LPS. Collectively, these results demonstrate that MHC class II utilizes a MyD88-mediated signaling mechanism when in contact with ligands such as SEs to induce pro-inflammatory cytokines.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • B-Lymphocytes
  • Cytokines / biosynthesis
  • Enterotoxins / immunology
  • Enterotoxins / metabolism*
  • Gene Expression Regulation / immunology
  • Histocompatibility Antigens Class II / immunology
  • Histocompatibility Antigens Class II / metabolism*
  • Humans
  • Inflammation
  • Mice
  • Mice, Knockout
  • Monocytes / immunology
  • Myeloid Differentiation Factor 88 / immunology
  • Myeloid Differentiation Factor 88 / metabolism*
  • Protein Binding / immunology
  • Signal Transduction / immunology*


  • Cytokines
  • Enterotoxins
  • Histocompatibility Antigens Class II
  • Myd88 protein, mouse
  • Myeloid Differentiation Factor 88
  • enterotoxin B, staphylococcal