Leprosy and Immune System: An Insight into the Innate Immune System

Innate immunity is a host immune mechanism to defend itself promptly. It includes physical and chemical barriers, cells in the circulation and tissues, several plasma proteins, and immune cells constituting phagocytic cells (monocytes/macrophages and neutrophils), dendritic cells, natural killer (NK) cells, blood proteins and cytokines. Leprosy is a chronic granulomatous disease caused by Mycobacterium leprae. Innate immune response in leprosy includes the role of pattern recognition receptor (PRR) in recognizing Mycobacterium leprae pathogen-associated molecular patterns (PAMPs), such as the Toll-like receptor (TLR)1, TLR2 and TLR6, nucleotide-binding oligomerization domain 2 (NOD2), cytokine release, macrophage and dendritic cells differentiation, and antimicrobial effector pathway. Recognition of microbial pathogen is followed by phagocytosis. In addition to phagocytosis, macrophages act as scavenger element to remove extracellular material such as oxidized lipid, vital for host lipid metabolism. Anti-microbial activity induced by vitamin D may also contribute to the disease outcome. The innate immune system's ability to instruct adaptive T cell response, mediated by dendritic cells, is part of the effective host defence in combating intracellular pathogens including leprosy. Additionally, host genetics and nutritional status still account for a substantial amount of disease susceptibility in leprosy requiring further studies to understand leprosy, specifically the immune system, comprehensively