Evaluation of peripheral blood leukocyte subpopulations by flow cytometry in calves treated with Mannheimia haemolytica leukotoxin

The aim of the study was to evaluate the effect of Mannheimia haemolytica leukotoxin (Lkt) on cellular immune response in clinically-healthy calves given intravenously 25 µg per animal of M. haemolytica Al Lkt. The alternations of peripheral blood leukocytes were examined with a flow cytometry. The Lkt treated calves were compared with the non-treated controls before (0) and 1, 2, 3, 4, 5, 6, and 24 h after the treatment. The following parameters were assayed: white blood cell (WBC) count, percentage of polymorphonuclear leukocytes (PMNL), mid-size leukocytes, total percentage of lymphocytes and their subsets: CD2⁺ (T lymphocytes), CD4⁺ (T helper lymphocytes), and CD8⁺ (T suppressor/cytotoxic lymphocytes) with CD4⁺: CD8⁺ratio, and also WC4⁺ cells (B lymphocytes). The obtained results showed that in the treated calves, the WBC count, the percentages of PMNL, mid-size leukocytes, and some subpopulations of peripheral lymphocytes (CD2⁺, CD4⁺, CD8⁺) were significantly lower compared with the controls during the first of three hours of the experiment, and then the parameters increased and returned to the physiological level.