Flow cytometric analysis of T-lymphocyte subsets in cats.

We report a rapid, reliable method for the immunophenotype analysis of feline lymphocytes. Fluorescein isothiocyanate (FITC) conjugated to murine monoclonal antibodies f43, Fel 7 and fCD8 was used to identify phenotypes corresponding to feline T-cells, CD4+ T cells and CD8+ T cells. For isolation of white blood cells, whole blood lysis was faster, less variable and required much less sample than density gradient separation. To identify feline CD4+ and CD8+ cells simultaneously, directly conjugated FITC-fCD8 and phycoerythrin (PE) fCD4 (Fel 7) were used in two-color analysis. The two T cell sub-populations were non-overlapping. Dual-label and single-label values were not significantly different. Mean lymphocyte subset percentages in conventional and specific-pathogen-free (SPF) cats did not differ significantly. These values were: pan T lymphocytes (f43), 54.8%, CD4+ cells (Fel 7), 33.9%, and CD8+ cells (fCD8), 19.1%. Mean CD4/CD8 ratio was 1.9 in normal cats; the range was 1.2-2.6.