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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., (Copyright © 2017. Published by Elsevier B.V.)

Maltose-binding protein (MBP) is a component of the maltose transport system of Escherichia coli. Our previous study found that MBP combined with Bacillus Calmette-Guerin (BCG) increases the percentage of activated macrophages in the spleen and the pinocytic activity of peritoneal macrophages in vivo. However, the effect of MBP alone on macrophages remains unclear. In the present study, the results showed that MBP enhanced LPS-stimulated macrophage activity in vivo. Subsequently, we investigated the regulatory effect of MBP on mouse peritoneal macrophages in vitro and the possible underlying mechanism. The results showed that MBP directly promoted macrophage phagocytic activity and increased the production of NO, IL-1β and IL-6. Notably, macrophage phenotypic analysis showed that MBP significantly increased iNOS, IL-12p70 and CD16/32. In contrast, MBP decreased the secretion of IL-10 and slightly decreased Arg-1 mRNA and CD206 protein expression. These results suggested that MBP activated macrophages and polarized them into M1 macrophages. Further study found that MBP directly bound to macrophages and upregulated TLR2 mRNA expression. This process was accompanied by a clear increase in MyD88 expression and phosphorylation of p38 MAPK and IκB-α, but these effects were largely abrogated by pretreatment with anti-TLR2 or anti-TLR4 antibodies. The effects of MBP on macrophage NO production were also partially inhibited by anti-TLR2 and/or anti-TLR4 antibodies. Furthermore, the effect of MBP on IL-12 and IL-10 secretion was largely influenced by the NF-κB inhibitor PDTC and the p38 MAPK inhibitor SB203580. These results suggest that MBP directly activates macrophages and induces M1 polarization through a process that may involve TLR2 and TLR4., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Maltose binding protein (MBP) is a component of the maltose transport system in the periplasm of Escherichia coli. It is commonly believed that MBP has minimal effects on the bioactivity, thus, it is widely used in the purification of recombinant proteins. Here, we found that the combined immunization with MBP and Bacillus Calmette-Guerin (BCG) significantly inhibited tumor growth compared with MBP or BCG immunization alone in a mouse lung carcinoma model. Further studies showed that MBP nonspecifically activated T helper 1 (Th1) cells and enhanced the BCG-induced Th1 cell activation. Moreover, MBP or BCG immunization alone increased the activities of natural killer (NK) cells and macrophages, and the combined immunization with MBP and BCG induced a synergistic effect on the activities of NK cells and macrophages. These results suggest that MBP possesses potent immune enhancement activities, and that the combination of MBP and BCG-induced synergistic antitumor effects might be mediated mainly through the activation of Th1 cells, NK cells and macrophages., (Copyright © 2010 Elsevier B.V. All rights reserved.)