This study sought to assess if chlorpyrifos (CPF) induced immunotoxic effects in orally-treated day-old broiler chicks. Groups of chicks received per os CPF diluted in xylene at 5, 10, and 20 mg/kg body weight (CPF-5, CPF-10, and CPF-20) orally daily for 15 days. Xylene and control groups received xylene alone (1 ml/kg BW) and physiological saline, respectively. At various times during/after the exposure regimens, different immune end-points were analyzed in the birds. Humoral immunity was examined by assessing antibody responses to sheep red blood cells. Cell-mediated immunity was measured via lymphoproliferative responses to avian tuberculin. Leukocyte phagocytic ability was measured using a carbon clearance assay. Results showed that CPF administered to broiler chicks caused a dose-dependent decrease in humoral immunity, cell-mediated immunity, and phagocytic activity. Dose- and time-related pathological changes were observed in bursa of Fabricius, spleen, and thymus in treated birds. These changes were mild, moderate, and severe, respectively, in the 5, 10, and 20 mg/kg CPF groups. The Bursa of Fabricius in treated birds showed increased inter-follicular connective tissue proliferation, severe moderate cytoplasmic vacuolation, edema, and degenerative changes such as pyknosis and fragmentation of nuclei that depleted the follicles of lymphoid cells. In the spleen, disorganization of follicular patterns, severe congestion, cytoplasmic vacuolation, degenerative changes, and hyperplasia of reticular cells were noted. The thymus in treated birds exhibited congestion, hyper-cellularity, and a presence of immature monocytes in the medullary region, as well as myoid cell necrosis. Taken together, these studies clearly demonstrated that chlorpyrifos could induce immunotoxicities in broiler birds.
Keywords: Broiler chicks; chlorpyrifos; immunological; toxic effects.