Date of Award

12-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Thandi M. Onami

Committee Members

Barry T. Rouse, Mark Y. Sangster, Tim E. Sparer, Chunlei Su

Abstract

Glycosylation is one of the most abundant post-translational modifications of proteins. Glycoproteins participate in virtually all aspects of cellular functions. ST6Gal I is a glycosyltransferase highly expressed by B and T cells. Here, we interrogated the role of ST6Gal I in viral specific B and T cell immune responses, as well as examined how loss of this enzyme impacted viral pathogenesis.

First, to understand how loss of ST6Gal I expression impacted viral specific humoral responses, we infected ST6Gal I-/- mice with influenza virus. We discovered that loss of ST6Gal I expression results in both reduced influenza specific antibodies levels and decreased viral-specific antibody secreting cells numbers. Following influenza infection, mice that received ST6Gal I-/- B cells showed reduced influenza-specific IgM responses compared to mice that received wild-type B cells. These experiments demonstrated that the expression of ST6Gal I by B cells is required for optimal viral-specific humoral response.

We further examined how loss of ST6Gal I expression impacted the anti-influenza IgA response. We observed that immune ST6Gal I-/- mice displayed higher viral specific IgA levels and altered sialylation of IgG and IgA, which have been implicated in a human disease, IgA nephropathy. Moreover, ST6Gal I-/- mice exhibited increased immunoglobulin deposition in kidney glomeruli following influenza infection. These data suggest that ST6Gal I deficiency, together with influenza infection, may result in the initiation of a kidney disease.

Finally, we examined how ST6Gal I expression regulated CD8 T cell responses. We discovered that ST6Gal I is differentially expressed during CD8 T cell activation. To understand its relevance, we infected ST6Gal I-/- mice and demonstrated that the early expansion of effector T cells was impaired in a cell intrinsic manner. Moreover, in the absence of ST6Gal I, the differentiation of CD8 T cells skewed towards memory precursor cells, whereas terminal effector cell expansion was impaired. Mechanistically, we identified delayed surface expression of IL-2Ralpha on ST6Gal I-/- CD8 T cells due to impaired IL-2/IL-2R signaling. These studies implicate that ST6Gal I expression enhances early proliferation of terminal effector CD8 T cells by promoting the rapid surface expression of IL2Ralpha during acute viral infection.



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