Objective: To analyze surface antigen expression and functional responses of leukocytes from calves heterozygous and homozygous for bovine leukocyte adhesion deficiency (BLAD).
Animals: 8 clinically normal calves, 4 calves heterozygous for BLAD, and 4 calves homozygous for BLAD.
Procedure: Surface antigen expression was examined by flow cytometric analysis of leukocytes stained with monoclonal antibodies. Neutrophil function analyses included phagocytosis and killing of Candida albicans and measurement of respiratory burst activity using cytochrome c and dihydrorhodamine 123 assays. Differential leukocyte counts also were performed.
Results: Leukocytes from heterozygous calves were similar to those of clinically normal calves with respect to surface antigen expression, C albicans phagocytosis and killing, and respiratory burst activity. In contrast, neutrophils from calves homozygous for BLAD had significantly reduced phagocytic and yeast-killing capacity but had higher respiratory burst activity than cells from clinically normal or heterozygous calves. Homozygous calves also had extreme neutrophilia and significantly more immature neutrophils.
Conclusions: The heterozygous BLAD genotype does not cause detectable functional differences in leukocytes, compared with those of clinically normal calves. In contrast, leukocytes from homozygous calves seem to upregulate alternative host defense capabilities (eg, respiratory burst activity) to partially compensate for the lack of typical adherence-dependent host defense functions.