Identification of koala T lymphocytes using an anti-human CD3 antibody

Previous attempts to identify T lymphocytes in the koala using cross reacting monoclonal antibodies (mAbs) against other species T cell antigens (Ags) and classical T cell lectins have proved unsuccessful. Recently a polyclonal rabbit Ab preparation directed at the epsilon chain of the human CD3 complex (anti-CD3) has become commercially available and has been shown to have broad cross-species reactivity. We have demonstrated that this anti-CD3 is suitable for labelling T cells from peripheral blood of koalas if the purified peripheral mononuclear cells (PMC) are first made permeable with mild fixation in buffered formal acetone. We have also been able to identify koala T cells in both formalin-fixed and frozen lymphoid tissues. Immunoprecipitation and Western blotting studies demonstrated that this anti-CD3 bound to a single 23 kDa polypeptide, probably representing the koala homologue of the human epsilon chain. This is the first report of successful identification of koala T cells and the first reported use of this anti-CD3 for the identification of peripheral circulating T lymphocytes in any species.