Abstract
ABSTRACT The comparison of the host immune response when challenged with pathogenic and nonpathogenic species of mycobacteria can provide answers to the unresolved question of how pathogens subvert or inhibit an effective response. We infected human monocyte derived macrophages (hMDMs) with different species of mycobacteria, in increasing order of pathogenicity, i.e. M. smegmatis, M. bovis BCG, and M. tuberculosis R179 that had been cultured in the absence of detergents. RNA was isolated post-infection and transcriptomic analysis using amplicons (Ampliseq) revealed 274 differentially expressed genes (DEGs) across three species, out of which we selected 19 DEGs for further validation. We used qRT-PCR to confirm the differential expression of 19 DEGs. We studied biological network through Ingenuity Pathway Analysis® (IPA) which revealed up-regulated pathways of the interferon and interleukin family related to the killing of M. smegmatis. Apart from interferon and interleukin family, we found one up-regulated (EIF2AK2) and two down-regulated (MT1A and TRIB3) genes as unique potential targets found by Ampliseq and qRT-PCR which may be involved in the intracellular mycobacterial killing. The roles of these genes have not previously been described in tuberculosis. Multiplex ELISA of culture supernatants showed increased host immune response toward M. smegmatis as compared to M. bovis BCG and M.tb R179. These results enhance our understanding of host immune response against M.tb infection.
Highlights
According to the World Health Organization (WHO) global tuberculosis (TB) report in 2018, TB is the number one infectious killer globally [1]
We examined differential gene expression during the infection of human monocyte derived macrophages (hMDMs) with pathogenic (M. tb R179; drug resistant Beijing genotype strain R220) and nonpathogenic (M. smegmatis) species of mycobacteria along with M. bovis Bacillus Calmette–Guerin (BCG) (BCG Tokyo 172 strain) [15 28 29,]
Ampliseq analysis of RNA derived from hMDMs before and after infection across three mycobacterial species identified overlapped 274 differentially expressed genes (DEGs) at 12-h post infection
Summary
According to the World Health Organization (WHO) global tuberculosis (TB) report in 2018, TB is the number one infectious killer globally [1]. Different species of mycobacteria have been shown to elicit different immune responses [2]. Pathogenic mycobacteria are known to survive inside the host by arresting phagosome maturation [3,4,5]. The pathogen survives inside the optimal environment of the phagosome and the mechanism responsible for its growth and survival inside the host is still unknown [6,7,8]. The enigma of the host response to effectively counter nonpathogenic bacteria but being unable to destroy pathogenic bacteria may be deciphered by comparing the host immune response toward these pathogenic and nonpathogenic infections. One of the most widely used approaches for evaluating the host response to
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