Immunophenotyping of canine T cell activation and proliferation by combined protein and RNA flow cytometry

The limited availability of canine-reactive monoclonal antibodies restricts the analyses of immune cell subsets and their functions by flow cytometry. The PrimeFlowTM RNA Assay may serve as a potential solution to close this gap. Here we report a blood immunophenotyping method utilizing combined protein- and RNA-based flow cytometry to characterize canine T cell activation and proliferation within individual cells. In this assay, CD69 expression was detected by an RNA probe and CD25 and Ki67 were detected by antibodies. Canine peripheral blood mononuclear cells (PBMCs) were stimulated with three agents with different modes of action, anti-CD3/ CD28 antibodies, phytohemagglutinin, or phorbol myristate acetate /ionomycin. Robust T cell activation (CD25+ and/or CD69+) and proliferation (Ki67+) were detected. Both CD69 and CD25 appear to be robust and sensitive T cell activation markers with early induction and low background expression. Upon stimulation, T cell proliferation occurred later than T cell activation and was associated with CD25 expression. This canine T cell activation and proliferation immunophenotyping method was evaluated in 5 independent experiments using PBMCs from 10 different beagle dogs with satisfactory assay performance. This method can greatly facilitate the evaluation of immune disease pathogenesis and immunotoxicity risk assessment in nonclinical drug development in canine.