Universität zu Köln

Subramanian, Senthil Kumar (2014). Differential Influence of Clinical Mycobacterium avium Strains on Distinct Autonomous Defense Capacities of Human Neutrophils. PhD thesis, Universität zu Köln.

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Abstract

Neutrophils are phagocytes that are known to be fast responders and reach the site of an infection as an innate immune response. Neutrophils, in addition to monocytes and macrophages, have been implicated during the initial phase of mycobacterial infection. However, neutrophils are less well studied than other components of the host response to mycobacteria such as the macrophages, the natural primary host cell and T cells. Whether neutrophils are able to actively kill mycobacteria and thus contribute to mycobacterial clearance remains controversial. Our group has shown that human neutrophils are able to phagocytize and kill the avian type strain Mycobacterium avium TMC 724 (M. avium) in vitro. In this study we used two clinical strains of M. avium hominissuis, SCH 228 and SCH 215 that have been previously characterized to be differential with regard to their generation time within macrophages as a feature of mycobacterial virulence. Such variation in virulence may be responsible for differences in disease outcome. Here we tried to understand the cell autonomous functions of neutrophils in mycobacterial infection and also how clinical isolates of M. avium hominissuis (SCH 228 and SCH 215) considered of high and low virulence impact on neutrophil functional capacities. Our study demonstrates that SCH 228 and SCH 215 limit the activation of human neutrophils by differentially down regulating the activation of p38 MAPK pathway. Such differential regulations promote bacterial survival by impeding the p38 MAPK-mediated immune functions such as ROS, degranulation and cytokine induction in neutrophils. To best of our knowledge, this is the first report on how the virulence of clinical M. avium hominissuis isolates impacts on various innate immune functions of human neutrophils. We also demonstrated the ability of degranulation from cytB/fMLP-activated human neutrophils in controlling the extracellular growth of clinical M. avium hominissuis isolates, SCH 228 and SCH 215. Furthermore, the degranulated supernatants from neutrophils infected with these isolates show the capacity to inhibit extracellular growth of Staphylococcus aureus whereas they have no bactericidal effect on SCH 228 and SCH 215 themselves. Investigation of neutrophil-macrophage interaction in the defense of these clinical M. avium isolates revealed that neither naïve nor LPS-stimulated neutrophils when co-cultured with infected human macrophages did impact on intra-macrophage bacterial survival of SCH 228 and SCH 215. However, macrophages infected with these isolates induce predominantly degranulation of specific/gelatinase granules in naïve neutrophils, indicating that neutrophil-macrophage interaction impacts on the microenvironment of local infection thereby potentially contributing to disease pathogenesis. Furthermore, this study underscores the importance of exosomes released from macrophages infected with M. avium as a cell-mediator molecule involved in the interaction of infected macrophages with other immune cells, as these exosomes attract human neutrophils. As a perspective, our finding that cytB/fMLP stimulated degranulation controls the extracellular growth of clinical M. avium hominissuis isolates, SCH 228 and SCH 215, encourages us to further carry out extensive comparative proteomic analyses of cytB/fMLP and M. avium stimulated supernatants from neutrophils in order to identify possible factors that might be able to control M. avium infection and may qualify as potential anti-mycobacterial drugs. Also, proteomic analysis of exosomes from infected macrophages suggests follow-up studies to identify the potential chemoattractive factors for neutrophils. This would allow one to study the role of such factor(s) present in the exosomes in the interaction of infected macrophages and neutrophils, and possibly, other immune cells.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Subramanian, Senthil Kumar kumar.senthil.s@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-56529
Date:	3 July 2014
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Institute for Genetics
Subjects:	Life sciences
Uncontrolled Keywords:	Keywords Language phd thesis English
Date of oral exam:	26 June 2014
Referee:	Name Academic Title Howard, Jonathan Prof. Dr. Uhlirova, Mirka Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/5652