Abstract
Leprosy is a chronic infection where the skin and peripheral nervous system is invaded by Mycobacterium leprae. The infection mechanism remains unknown in part because culture methods have not been established yet for M. leprae. Mce1A protein (442 aa) is coded by mce1A (1326 bp) of M. leprae. The Mce1A homolog in Mycobacterium tuberculosis is known to be associated with M. tuberculosis epithelial cell entry, and survival and multiplication within macrophages. Studies using recombinant proteins have indicated that Mce1A of M. leprae is also associated with epithelial cell entry. This study is aimed at identifying particular sequences within Mce1A associated with M. leprae epithelial cell entry. Recombinant proteins having N-terminus and C-terminus truncations of the Mce1A region of M. leprae were created in Escherichia coli. Entry activity of latex beads, coated with these truncated proteins (r-lep37 kDa and r-lep27 kDa), into HeLa cells was observed by electron microscopy. The entry activity was preserved even when 315 bp (105 aa) and 922 bp (308 aa) was truncated from the N-terminus and C-terminus, respectively. This 316–921 bp region was divided into three sub-regions: 316–531 bp (InvX), 532–753 bp (InvY), and 754–921 bp (InvZ). Each sub-region was cloned into an AIDA vector and expressed on the surface of E. coli. Entry of these E. coli into monolayer-cultured HeLa and RPMI2650 cells was observed by electron microscopy. Only E. coli harboring the InvX sub-region exhibited cell entry. InvX was further divided into 4 domains, InvXa—InvXd, containing sequences 1–24 aa, 25–46 aa, 47–57 aa, and 58–72 aa, respectively. Recombinant E. coli, expressing each of InvXa—InvXd on the surface, were treated with antibodies against these domains, then added to monolayer cultured RPMI cells. The effectiveness of these antibodies in preventing cell entry was studied by colony counting. Entry activity was suppressed by antibodies against InvXa, InvXb, and InvXd. This suggests that these three InvX domains of Mce1A are important for M. leprae invasion into nasal epithelial cells.
Highlights
Hansen’s disease is a chronic infection with acid fast bacillus where skin and peripheral nerves are damaged by the infection with Mycobacterium leprae (M. leprae)
Mce1A protein is a cell surface protein encoded by the mce1A region of mce1 locus of M. tuberculosis and M. leprae, and is involved in the bacteria’s invasion into epithelial cells
The present study revealed that the active sequence of M. leprae involved in the invasion into nasal mucosa epithelial cells is present in the 316–531 bp region of mce1A
Summary
Hansen’s disease is a chronic infection with acid fast bacillus where skin and peripheral nerves are damaged by the infection with Mycobacterium leprae (M. leprae). Tuberculoid leprosy triggers predominantly cellular immunity response, and is called paucibacillary, because very few are detected at the focus of infection or nasal mucosal membrane. Lepromatous leprosy triggers predominantly humoral immunity, and is called multibacillary, because it is detected in a large amount at the focus of infection and, in particular, from nasal mucosal membrane. Infection of Hansen’s disease has conventionally been considered to occur through close skin contact or through wounds, but recently another infection mode, in which M. leprae in the aerosol from nasal discharge of lepromatous leprosy patients invades into the upper respiratory tract and nasal mucosal membrane to cause infection, has come to be recognized [3,4,5,6,7,8,9,10]. The invasion mechanism in this infection mode has not been extensively studied yet
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