| Both T cell development and activation rely not only on the binding of the TCR to its corresponding ligand, but also on the interactions of numerous accessory molecules. One such molecule is CD45, which although well characterized in terms of its cytoplasmic domain and phosphatase activity, little is known regarding its complex and strictly regulated extracellular domain. It has been proposed that its activity is regulated through binding of specific ligands to different forms of this molecule, likely through presented carbohydrates. To this end, we have characterized three different C-type lectin receptors all of which are expressed on professional APCs. Although binding appeared independent of CD45, two lectins, CIRE and Dectin-1, did recognize T cells and positively regulated their activity. Additionally, studies using antibodies revealed that binding of specific epitopes of CD45 can elicit significant and varied effects, implicating CD45-ligand interactions in the regulation of T cell development and activation. |
