Caspase activation may be associated with Mycobacterium avium pathogenicity

Area of Science:

• Immunology
• Microbiology
• Cellular Biology

Background:

• Mycobacterium avium (M. avium) infection causes disseminated disease in immunocompromised individuals.
• M. avium infection in goats mimics Crohn's disease, with colony morphotypes correlating to pathogenicity.
• Smooth-transparent (SmT) M. avium morphotypes are more virulent, inducing lower levels of interleukin (IL)-1beta and IL-18 compared to avirulent smooth-domed (SmD) morphotypes.

Purpose of the Study:

• To investigate caspase activation in human monocytes following M. avium infection.
• To determine the role of differential caspase activity in M. avium pathogenicity.

Main Methods:

• Human monocytes were infected with M. avium.
• Caspase-1 and caspase-3 activation and mRNA expression were analyzed.
• The impact of caspase inhibition on IL-1beta production was assessed.

Main Results:

• M. avium infection upregulated caspase-1 mRNA expression in monocytes.
• Monocytes infected with SmD morphotypes showed significantly higher activated caspase levels than those infected with SmT morphotypes.
• Caspase-1 inhibition reduced IL-1beta production in both SmT- and SmD-infected monocytes.
• Caspase-3 inhibition reduced IL-1beta production in SmD-infected monocytes but not in SmT-infected monocytes.

Conclusions:

• Differential caspase activation, particularly caspase-1, occurs in human monocytes upon M. avium infection.
• The selective induction of caspase-1 and lack of caspase-3 activation by virulent SmT morphotypes may contribute to M. avium pathogenicity.
• These findings highlight the role of host caspase responses in M. avium pathogenesis.