Biology subjects

Ramakrishnan, L.

Publications and source records attributed to Ramakrishnan, L..

5 recordsLinked to original sources

bioRxiv2018

Macrophage-induced rifampin tolerance across Mycobacterium tuberculosis lineages is Rv1258c-dependent

The Mycobacterium tuberculosis (Mtb) Lineage 4 strains CDC1551 and H37Rv develop tolerance to multiple antibiotics upon macrophage residence. Genetic mutation of the efflux pump Rv1258c in CDC1551 abolishes rifampin tolerance but not isoniazid tolerance. Here we show that clinical isolates from the other predominant Mtb lineages developed macrophage-induced isoniazid tolerance. Furthermore, all lineages developed rifampin tolerance except Lineage 2 Beijing strains, which are natural Rv1258c mutants. Thus macrophage-induced antibiotic tolerance is featured across the majority of Mtb lineages. Our findings further link Rv1258c to rifampin tolerance among clinical isolates.

microbiology↗

bioRxiv2017

A Zebrafish Model For Ocular Tuberculosis

Ocular tuberculosis (TB) commonly causes severe inflammation and vision loss in TB-endemic countries. The mechanism by which tuberculous infection becomes established in the eye is poorly understood. We used Mycobacterium marinum-infected zebrafish larvae to study the early pathogenesis of ocular TB and found hematogenous bacterial seeding of the eye despite a functional blood retinal barrier. Prototypical early granulomas formed that involved the retinal vasculature and retinal pigment epithelium-choroid complex; characteristic locations for human ocular TB. Peripheral blood monocytes were recruited to the growing granuloma suggesting that the immune privileged nature of the eye is breached by this inflammatory focus.\n\nConflict of interestnone disclosed\n\nFundingThis work was supported in part by a Short-term fellowship to SB by Department of Health Research, Government of India.

microbiology↗

bioRxiv2017

Phenolic glycolipid facilitates mycobacterial escape from a microbicidal population of tissue-resident macrophages

Mycobacterium tuberculosis enters the host in aerosol droplets deposited in lung alveoli where the bacteria first encounter lung-resident alveolar macrophages. We studied the earliest mycobacterium-macrophage interactions in the optically transparent zebrafish. We find that the first-responding resident macrophages can phagocytose and eradicate infecting mycobacteria. So, to establish a successful infection, mycobacteria must escape out of the initial resident macrophage into growth-permissive monocytes. We define a critical role for the membrane phenolic glycolipid (PGL) in engineering this transition to a permissive niche. PGL activates the STING cytosolic sensing pathway, thereby inducing the chemokine CCL2 that recruits permissive peripheral monocytes. The bacteria then transfer from resident macrophage to recruited monocyte via transient fusion of the two immune cells. We show that interrupting this bacterial strategy so as to prolong the mycobacterial sojourn in resident macrophages promotes clearing of infection. Because PGL-dependent CCL2 induction is conserved in human alveolar macrophages, our findings suggest the potential of immunological or pharmacological PGL-blocking interventions to prevent tuberculosis.

immunology↗

bioRxiv2017

A Zebrafish Model For Mycobacterium leprae Granulomatous Infection

Understanding the pathogenesis of leprosy granulomas has been hindered by a paucity of tractable experimental animal models. Mycobacterium leprae, which causes leprosy, grows optimally at ~30{degrees}C, so we sought to model granulomatous disease in the ectothermic zebrafish. We find noncaseating granulomas develop rapidly, and eventually eradicate infection. rag1 mutant zebrafish, which lack lymphocytes, also form noncaseating granulomas with similar kinetics, but these control infection more slowly. Our findings establish the zebrafish as a facile, genetically tractable model for leprosy, and reveal the interplay between innate and adaptive immune determinants mediating leprosy granuloma formation and function.

microbiology↗

bioRxiv2017

A Macrophage Response To Mycobacterium leprae Phenolic Glycolipid Initiates Nerve Damage In Leprosy

Mycobacterium leprae causes leprosy, and is unique among mycobacterial diseases in producing peripheral neuropathy. This debilitating morbidity is attributed to axon demyelination resulting from direct interactions of the M. leprae-specific phenolic glycolipid 1 (PGL-1) with myelinating glia, and their subsequent infection. Here, we use transparent zebrafish larvae to visualize the earliest events of M. leprae-induced nerve damage. We find that demyelination and axonal damage are not directly initiated by M. leprae but by infected macrophages that patrol axons; demyelination occurs in areas of intimate contact. PGL-1 confers this neurotoxic response on macrophages: macrophages infected with M. marinum expressing PGL-1 also damage axons. PGL-1 induces nitric oxide synthase in infected macrophages, and the resultant increase in reactive nitrogen species damages axons by injuring their mitochondria and inducing demyelination. Our findings implicate the response of innate macrophages to M. leprae PGL-1 in initiating nerve damage in leprosy.

microbiology↗