Escherichia coli maltose-binding protein (MBP) activates mouse Th1 through TLR2-mediated MyD88-dependent pathway and TLR4-mediated TRIF-dependent pathway.

MBP (maltose-binding protein) is a component of Escherichia coli. Our previous study found that MBP directly induces the activation of Th1 (T helper type 1), but the molecular mechanism remains unclear. In the present study, CD4+ T cells were purified from the spleens of normal mice using antibody-coated immunomagnetic beads by negative selection. CD4+ T cells activated with a CD3/CD28 antibody were stimulated with MBP. The results indicated that MBP elevated IFN-γ mRNA levels in activated CD4+ T cells and promoted IFN-γ production from activated CD4+ T cells. To explore TLR2/TLR4 signaling involved in the mechanism of MBP-induced activation of Th1, we further detected downstream molecules of TLR2/TLR4 signaling. We found that MBP increased the mRNA levels of MyD88, TRAF6, TRIF and TRAF3 expressed in CD4+ T cells. The results suggested that downstream molecules of TLR2/TLR4 signaling may be involved in MBP-induced activation of CD4+ T cells. Furthermore, MyD88, TRIF, TRAF3 and TRAF6 expressed in activated CD4+ T cells blocked with anti-TLR2 antibody or anti-TLR4 antibody followed by treatment with MBP were detected via RT-PCR and western blotting, respectively. MBP decreased the production of IFN-γ in CD4+ T cells in the presence of anti-TLR2, accompanied by the down-regulated expression of MyD88 and TRAF6. However, MBP increased the production of IFN-γ in CD4+ T cells in the presence of anti-TLR4 antibody accompanied by the up-regulated expression of MyD88 and the down-regulated expression of TRIF, TRAF6 and TRAF3. The results suggested that the MyD88-dependent pathway of TLR2 and TRIF-dependent pathway are involved in the mechanism of Th1 activation induced by MBP. Our study has contributed to the clarification of the molecular mechanism of MBP-induced activation of CD4+ T cells.