Background: Since macrophages are one of the major cell types involved in the Mycobacterium leprae immune
response, roles of the M1 and M2 macrophage subpopulations have been well defined. However, the role of M4
macrophages in leprosy or other infectious diseases caused by mycobacteria has not yet been clearly characterized.
This study aimed to investigate the presence and potential role of M4 macrophages in the immunopathology
of leprosy.
Methods: We analyzed the presence of M4 macrophage markers (CD68, MRP8, MMP7, IL-6, and TNF-?) in 33
leprosy skin lesion samples from 18 patients with tuberculoid leprosy and 15 with lepromatous leprosy by
immunohistochemistry.
Results: The M4 phenotype was more strongly expressed in patients with the lepromatous form of the
disease, indicating that this subpopulation is less effective in the elimination of the bacillus and consequently is associated
with the evolution to one of the multibacillary clinical forms of infection.
Conclusion: M4 macrophages are one of the cell types involved in the microbial response to M. leprae and probably are
less effective in controlling bacillus replication, contributing to the evolution to the lepromatous form of the disease.
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