Alterations in the lymphocytic and mononuclear phagocytic systems of turkey poults associated with exposure to poult enteritis and mortality syndrome

In vivo and in vitro mononuclear phagocytic system functions, expression of lymphocyte subset cell surface markers in the thymus and bursa of Fabriciu s, and lymphocyte subset dynamics during the course of poult enteritis and mortality syndrome (PEMS) were examined. PEMS is an acute, transmissible, i nfectious intestinal disease accompanied by high mortality and morbidity. T he etiology of this multifactorial disease remains to be elucidated; howeve r, turkey coronavirus was initially assumed to be one of the primary agents involved. Further investigation demonstrated that turkey coronavirus was n ot always detectable in poults exhibiting PEMS symptoms, and, thus, PEMS po ults began to be identified as positive or negative for turkey coronavirus. In each trial, uninfected hatchmate controls were compared with turkey pou lts that were contact exposed to PEMS poults at 7 days of age. Following in travenous inoculation, control poults cleared Escherichia coli from their c irculation by 60 min, whereas viable E. coli were still present in the circ ulation of PEMS poults at 60 min postinoculation. Inflammatory response mea sured by Sephadex-elicited abdominal exudate cell recruitment and the adher ence potential of abdominal exudate cells was not significantly different b etween uninfected and PEMS poults. The percentage of glass-adherent abdomin al exudate macrophages was higher in PEMS poults. However, the ability of t hese macrophages to phagocytize sheep red blood cells and the average numbe r of sheep red blood cells per phagocytic macrophage were both lower compar ed with uninfected controls. CD4(+) expression in thymic tissue of PEMS pou lts at 9 days postinfection was significantly lower. The CD4(+):CD8(+) lymp hocyte ratio in peripheral blood leukocytes from coronavirus-negative PEMS poults was lower than that from both uninfected and coronavirus-positive PE MS poults at 14 days postinfection. In the spleen, the CD4(+):CD8(+) lympho cyte ratio was higher in coronavirus-positive PEMS poults as compared with the other treatments. In conclusion, immune system dysfunction in PEMS is a ssociated with impaired mononuclear phagocytic system function and alterati ons in lymphocyte populations.