TIM-3 and Galectin-9 Regulation of Effector T cell Function and Activation

Su, Ee Wern (2011) TIM-3 and Galectin-9 Regulation of Effector T cell Function and Activation. Doctoral Dissertation, University of Pittsburgh.

PDF - Primary Text Restricted to University of Pittsburgh users only until 09 May 2016. Download (2976Kb) | Request a copy

Abstract

The T cell Immunoglobulin Domain and Mucin Domain 3 (TIM-3) is a type I glycoprotein expressed primarily on the surface of activated T cells and myeloid cells. The extracellular domain of TIM-3 consists of an IgV domain and a mucin domain with several sites for N- and O-linked glycosylation. The IgV domain is important for binding of TIM-3 to two of its known ligands, a β-galactoside binding lectin known as galectin-9 (Gal-9) and phosphatidylserine, a marker of early apoptosis. The cytoplasmic tail of TIM-3 has six conserved tyrosines, although their role in modulating downstream signaling pathways has yet to be determined. TIM-3 is widely regarded as a negative regulator of effector T cell function and viability. TIM-3 is also upregulated on exhausted T cells and is postulated to have a role in the development and/or maintenance of T cell exhaustion. However, the exact regulation of T cells by TIM-3 has not been fully established for several reasons. TIM-3 and at least one of its ligand is expressed on both T cells and antigen presenting cells (APC). Therefore, it is not clear whether TIM-3 antibodies or Tim-3 Ig fusion proteins block the ligation of TIM-3 on T cells or on APCs to enhance effector T cell function. Additionally, gal-9 can also induce apoptosis in cells lacking the expression of TIM-3 and has been shown to positively regulate other cell types such as dendritic cells and mast cells. As TIM-3 is becoming an increasingly attractive therapeutic target because of its ability to reverse exhaustion in T cells, it is important to determine the regulatory nature of TIM-3 on T cells. To do this, we expressed Tim-3 ectopically in Tim-3- Jurkat T cells and observed that Tim-3 enhances instead of inhibits signaling downstream of the T-cell receptor and co-stimulator, CD28. Then, using a series of truncation and point mutants of Tim-3, we determined that Y256 and Y263 are the most crucial of the six conserved tyrosines in mediating Tim-3 signaling. Another unexpected finding was that in addition to apoptosis, gal-9 also induces the secretion of pro-inflammatory cytokines from T helper subsets independently of Tim-3.

Actions (login required)