Mycobacterium leprae upregulates IRGM expression in monocytes and monocyte-derived macrophages.

Leprosy is caused by the infection of Mycobacterium leprae, which evokes a strong inflammatory response and leads to nerve damage. Immunity-related GTPase family M protein (IRGM) plays critical roles in controlling inflammation. The objective of the study was to investigate whether IRGM is involved in the infection of M. leprae. Levels of IRGM were assessed in M. leprae-infected CD4(+) T cells, monocytes, and monocyte-derived macrophages. Data revealed that both protein and mRNA levels of IRGM were increased in monocytes after M. leprae infection. Interestingly, monocyte-derived macrophages showed more prominent IRGM expression with M. leprae infection, whereas the bacteria did not affect IRGM in CD4(+) T cells. Furthermore, we assessed levels of IRGM in CD4(+) T cells and monocytes from 78 leprosy patients and 40 healthy controls, and observed upregulated protein level of IRGM in the monocytes from leprosy patients. Also, IRGM expression was inversely correlated with the severity of the disease. These findings suggested a close involvement of IRGM in M. leprae infection and indicated a potential mechanism of defending M. leprae infection.