Frequency of association of noncytopathic bovine viral diarrhea virus with bovine neutrophils and mononuclear leukocytes before and after treatment with trypsin

Enriched populations of neutrophils and mononuclear leukocytes from 9 cattle persistently infected with noncytopathic bovine viral diarrhea virus were analyzed for frequency of association with virus, using flow cytometric procedures. Trypsinization of neutrophils decreased the frequency of viral association from 0.82% to 0.49%. Similar treatment of mononuclear leukocytes decreased the frequency of viral association from 5.53% to 4.81%. Results of immunocytochemical procedures to locate viral antigen were inconclusive for neutrophils, but viral antigen was found in the cytoplasm of mononuclear leukocytes. A distinct and highly pure population of eosinophils was identified during flow cytometric analysis of neutrophil populations from 2 of 9 cattle.