ANALYSIS OF FELINE DUAL LYMPHOCYTE POPULATIONS OBSERVED BY FLOW-CYTOMETRY

Two discrete lymphocyte populations were observed commonly on flow cyt ometric analysis (FCM) of feline lymphocyte subsets. The identity of t hese populations as small and large lymphocytes was established by cor relating data from FCM with that from peripheral blood films. Dual lym phocyte populations were more likely to be seen in feline immunodefici ency virus-positive (FIV- + ve) cats but their occurrence was not affe cted by health status, age, gender or breed. FIV- + ve cats had a sign ificantly higher proportion of large lymphocytes than FIV-negative (FI V- - ve) cats. However, FIV- + ve cats had significantly fewer small l ymphocytes than FIV- - ve cats but similar numbers of large lymphocyte s.Lymphocyte subset analysis revealed that small lymphocytes had a gre ater proportion of CD4 + cells than large lymphocytes, regardless of t he FIV or health status of the cat. In FIV- - ve cats, small lymphocyt es had a greater proportion of Pan T + lymphocytes than large lymphocy tes, but the converse was seen in FIV- + ve cats. The proportion of CD 8 + cells was higher in small lymphocytes than large lymphocytes in we ll FIV- - ve cats but this distinction was not seen in sick FIV- - ve cats or FIV- + ve cats of any health status. Regardless of health stat us, FIV- + ve cats had a lower absolute count of small lymphocytes whi ch were T cells (due to lower numbers of both CD4 + and CD8 + cells) t han FIV- - ve cats. The numbers of small B cells were similar for both FTV- + ve and FIV- - ve cats. However, there were no differences betw een FIV- + ve and FIV- - ve cats in the absolute values of any subset of the large lymphocytes, which suggested that FIV may affect only sma ll lymphocytes. Statistically, the inclusion or exclusion of the large lymphocyte population for routine lymphocyte subset analysis did not affect the overall results. However, because there were significant di fferences in subset distribution between small and large lymphocytes, analysis of both groups should be included in studies examining the ro le of lymphocytes in disease.