Innate immune receptors in development of Mycobacterium tuberculosis infection

Abstract

According to the World Health Organization, over 10 million new tuberculosis cases are reported annually worldwide. According to the 2017 Federal State Statistics Service Report, incidence rate for active TB infection in the Russian Federation was 109.8 cases per 100,000 population, of which 41.3% accounted for chronic disease form. Regardless of climatic conditions, high prevalence of TB infection, is not only due to high Mycobacterium tuberculosis viability, but also its ability for long persistence in human body and reactivation after an unlimited period of dormancy. The outcome of infection is largely determined by host immunoreactivity and its ability to develop protective immune response. In addition, status of immune system also underlies tuberculosis course after the onset: either as a localized form, or as a form with extensive damage to the lungs and even other organs observed in generalized infection. In recent decades, a great attention was paid to examining mechanisms of adaptive cell immunity played in pathogenesis of TB infection. No doubt, adaptive immunity is a powerful defense system providing a targeted specific immune response, but now it is becoming clear that it represents solely an effector arm of innate immunity. Innate immunity is a phylogenetically more ancient, inherited system largely aimed at ensuring rapid pathogen elimination and preventing development of infection at early stages when adaptive immunity ongoing antigen-specific maturation. Mechanisms of innate immunity mediated by cells, diverse receptors, molecules and their complexes, found on various cells. Activation of innate immunity begins with recognition of conserved molecular groups present in various pathogens called pathogen-associated molecular patterns (PAMPs), which are sensed by pathogen recognition receptors (PRRs). Here, we review current data on the role of innate receptors in recognizing M. tuberculosis-derived PAMPs, production of immunoregulatory cytokines and activation of signaling pathways playing a crucial role in the regulation of necroptosis, apoptosis and autophagy of infected macrophages. Significance of innate mucosal factors in implementing immune response to M. tuberculosis is discussed. In particular, Toll-like receptors, scavenger-receptors, mannose receptor, DC-SIGN etc. were described to participate in development of M. tuberculosis immunity. The data on single nucleotide polymorphic variants for innate genes are shown, which predispose to developing tuberculosis and affecting its course.