Abstract
Mycobacterium tuberculosis (MTB) persistently infects and survives within the host macrophages. Substantial genotypic variation exists among MTB strains which correlate with their interactions with the host. The present study was designed to establish a correlation, if any, between infection and induction of innate immune response by genetically diverse drug resistant MTB isolates from India. For this purpose, three clinical isolates from ancient and modern lineages, along with H37Ra and H37Rv were evaluated for intracellular growth, phagocytic index, induction of proinflammatory cytokines and apoptosis following infection in THP-1 cell line. A wide variation in the induction of cytokines was revealed subsequent to infection with different strains. EAI-5 strain from ancient lineage 1, induced higher proinflammatory responses, higher apoptosis and moderate intracellular growth compared to other strains, in contrast, for Beijing strain of modern lineage 2, all three parameters were lowest among the clinical isolates. Further, the responses induced by LAM-6 from modern lineage 4 were at a moderate level, similar to the laboratory strain H37Rv which also belongs to lineage 4. Thus, these profiles were specific to their respective lineages and/or genotypes and independent of their drug resistance status. Further, a positive correlation, among TNF-α, IL-1β, IL-6 and IL-12 induced in infected THP-1 cells was demonstrated. In addition, induction of all pro-inflammatory cytokines correlated well with the host cell apoptosis. A positive correlation was observed between phagocytic index in the category of ‘>10 bacilli/cell’ and induction of apoptosis, only for virulent strains, indicating that initial accumulation of MTB strains inside the host cell may be an important determining factor for different innate responses.
Highlights
Tuberculosis (TB), the most prevalent infectious disease in the world, causes 1.4 million deaths each year including nearly 3, 50,000 deaths in India [1]
A positive correlation was observed between phagocytic index in the category of ‘.10 bacilli/cell’ and induction of apoptosis, only for virulent strains, indicating that initial accumulation of Mycobacterium tuberculosis (MTB) strains inside the host cell may be an important determining factor for different innate responses
The presence of intact TbD-1 region confirmed that EAI strain in the study was of an ancient lineage and its absence indicated that LAM and Beijing belonged to modern lineages
Summary
Tuberculosis (TB), the most prevalent infectious disease in the world, causes 1.4 million deaths each year including nearly 3, 50,000 deaths in India [1]. The innate immune responses to Mycobacterium tuberculosis (MTB), a causative agent of TB, by macrophages and dendritic cells (DC) play a crucial role in the host defense [2,3]. The induction of the immune responses depends on the complex interplay between the host and the pathogen which may contribute to variations in immunopathology and transmission of the disease. The diversity in MTB genome, especially in the human-adapted strains, was demonstrated by evaluating polymorphisms at insertion elements, spacer elements in the direct repeat region and mycobacterial interspersed repetitive unit [9,10]. It was reported that lineages 1, 5 and 6 were ancient and; 2, 3 and 4 were modern on the basis of TbD1 analysis
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