Mononuclear phagocytes of transport-stressed horses with viral respiratory tract infection

SUMMARY Twelve horses comprised 3 treatment groups; all horses in 2 of the groups had recently been transported and had clinical and laboratory evidence of respiratory tract infection, with equine influenza type 2 virus being the principal pathogen. Mononuclear phagocytes and other leukocytes from blood, lung, and peritoneal cavity were studied in phagocytosis and erythrocyte-antibody (ea) rosette assays. Total numbers of pulmonary alveolar macrophages were increased over control values in bronchoalveolar lavage (bal) fluid of group 3 horses after recovery from influenza (P < 0.02), whereas the increase in neutrophils in the fluid of those horses approached significance. Lymphocytes in bal fluid of group 3 horses (after recovery from influenza) were in larger proportion than those in fluid of group 1 horses during acute influenza (P < 0.05). Pulmonary alveolar macrophages of group 1 horses formed a lower percentage of ea rosettes than did those of controls (P < 0.01) or group 3 horses (P < 0.02). The differential counts of peritoneal macrophages and neutrophils in horses of groups 1 and 3 were virtually identical at the first collection, but differed from controls at the second collection 4 weeks later; peritoneal macrophages were reduced (P < 0.01), whereas peritonea! neutrophils were increased (P < 0.01). Peritoneal macrophages and peritoneal neutrophils of horses with acute influenza were phagocytic in larger proportion than were those in controls at both collection times (P < 0.01 and P < 0.01 for peritoneal macrophages, and P < 0.01 and P < 0.05 for peritoneal neutrophils, respectively), Peritoneal macrophages displayed immunoglobulin G receptors (ea rosettes), but did not differ in proportion between groups.