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Direct Inhibition of CD4+ T-cell Activation by Mycobacterium tuberculosis Cell Wall Glycolipids

Mahon, Robert Norman, III
http://rave.ohiolink.edu/etdc/view?acc_num=case1275668686

Abstract Details

2010, Doctor of Philosophy, Case Western Reserve University, Pathology.
For Mycobacterium tuberculosis (MTB) to survive against a robust CD4+ T-cell response, multiple immune evasion mechanisms may be necessary. These include indirect effects through inhibition of Class II Major Histocompatibility Complex (MHC-II) antigen processing, mediated by MTB lipoproteins. This study tested whether MTB could directly inhibit CD4+ T-cell activation. Murine CD4+ T-cells were activated independent of antigen presenting cell (APC) with antibodies against CD3 and CD28, and found to produce less IL-2 and proliferate less when activated in the presence of MTB. Experiments with fractions of MTB found that the cell wall was the most potent inhibitory fraction and identified cell wall glycolipids, particularly mannose-capped lipoarabinomannan (ManLAM) as most potent. Inhibition by ManLAM was neither T-cell subset (naïve CD4, memory CD4+, activated CD4+, CD8+) nor species-specific (murine, human). Inhibition was not associated with decreased T-cell receptor (TCR) expression, or IL-2 signaling. Surface expression of CD69 was suppressed suggesting that ManLAM blocked TCR signaling. Further analysis determined that bypassing proximal TCR signaling by stimulating downstream signaling pathways, including protein kinase C and Ca2+, prevented inhibition. Examination of proximal signaling found that ManLAM decreased tyrosine phosphorylation of Lck, ZAP-70, and LAT. Several mechanisms for how ManLAM inhibits proximal TCR signaling were analyzed. Analysis of the Csk negative regulatory pathway of Lck showed that ManLAM did not affect phosphorylation of Lck at Tyr505. Isolation of lipid rafts by sucrose gradient ultracentrifugation confirmed that ManLAM was present within the lipid rafts of T-hybridoma cells. Inhibition of proximal TCR signaling was temperature sensitive suggesting that insertion of ManLAM into lipid rafts was necessary to inhibit T-cell activation. Insertion of ManLAM into lipid rafts did not affect the localization of Lck or LAT within the lipid rafts of resting or anti-CD3 stimulated T-hybridoma cells. These results identified a novel mechanism for direct inhibition of T-cell activation by microbial glycolipids and have developed a new area of research that may not only increase our understanding of how MTB evades host adaptive immunity but also how proximal T-cell signaling is controlled.
W. Henry Boom, PhD (Advisor)
Clifford Harding, M.D./Ph.D. (Advisor)
George Dubyak, Ph.D. (Committee Chair)
Alan Levine, Ph.D. (Committee Member)
Clive Hamlin, Ph.D. (Committee Member)
128 p.
Immunology
tuberculosis; T-cells; activation; signaling; glycolipid; lipid raft; ZAP-70; ManLAM

Recommended Citations

Citations

  • Mahon, III, R. N. (2010). Direct Inhibition of CD4+ T-cell Activation by Mycobacterium tuberculosis Cell Wall Glycolipids [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1275668686

    APA Style (7th edition)

  • Mahon, III, Robert. Direct Inhibition of CD4+ T-cell Activation by Mycobacterium tuberculosis Cell Wall Glycolipids. 2010. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1275668686.

    MLA Style (8th edition)

  • Mahon, III, Robert. "Direct Inhibition of CD4+ T-cell Activation by Mycobacterium tuberculosis Cell Wall Glycolipids." Doctoral dissertation, Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1275668686

    Chicago Manual of Style (17th edition)

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© 2010, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.