Mechanism Of IRAK-M Of Macrophages Promoting Intracellular Survival Of Mycobacterium Tuberculosis

Objective: Intracellular bacterium, Mycobacterium tuberculosis, infects specifically macrophages as host cells. IRAK-M, a member of IRAK family, is a negative regulator in TLR signaling and specifically expresses in monocytes and macrophages. To explore the role of IRAK-M in intracellular growth of M. tb and macrophage polarization, for deeply understanding the pathogenesis of M. tb, significance of IRAK-M to innate immunity and pathogen-host interaction.Methods: Immunofluorescence, Western blot and immunohistochemistry were used to detect the expression of IRAK-M in M. tb infected macrophages and in tissue of pulmonary tuberculosis. Cell systems of IRAK-M knockdown and over-expression were constructed, investigating intracellular survival of M. tb with acid-fast staining and colony forming units. M. tb H37 Rv infected IRAK-M knockdown U937 cells and M1-type macrophage molecules p STAT1 and i NOS, M2-type macrophage molecules p STAT6 and Arg-1 were detected using Western blot. U937 cells were firstly stimulated with immunostimulant Cp G7909 into M1 status and then infected with M. tb H37 Rv. Immunofluorescence and Western blot were performed to detect IRAK-M, IRAK4 and i NOS, to evaluate the effect of IRAK-M to Cp G7909 directed M1-type polarization of macrophages in M. tb infection. Molecules related with regulation of macrophage's bactericidal ability such as Hif-1 and phosphorylated ERK1/2 were detected with immunohistochemistry and Western blot.Results: IRAK-M increased in M. tb infected macrophage cells and also in human lung tissue of pulmonary tuberculosis. IRAK-M over-expression resulted in higher bacterial load, while IRAK-M interference resulted in lower bacterial load in M. tb infected cells. During M. tb infection, IRAK-M knockdown induced M1-type, while inhibited M2-type polarization of macrophage. M1-type polarization of U937 cells induced by Cp G7909 was inhibited by M. tb infection, which was reversed by IRAK-M knockdown in U937 cells. IRAK-M affected Hif-1 and MAPK signaling cascade during M. tb infection.Conclusions: Conclusively, in current work, it was found that IRAK-M of macrophages might be utilized by M. tb to benefit M. tb intracellular growth, regulate macrophage polarization, and affect Th1-type immunity of the host, which is helpful to understanding the pathogenesis of M. tb.