Heterophils are decisive components in the early responses of chickens to Salmonella enteritidis infections.

Chickens injected with 5-fluorouracil (5-FU) were found to have a three- to nine-fold reduction in circulating heterophils without a reduction in the number of circulating mononuclear cells. A 50% organ invasive dose (ID50) for orally and intravenously administered Salmonella enteritidis (SE) was established in the heteropenic chickens. When challenged orally, about 150-fold fewer SE cells were required for organ invasion in the 5-FU-treated chickens; whereas an intravenous challenge of the heteropenic chickens required about 4000-fold fewer bacteria for organ invasion than found in the control birds. Significant (P < 0.0001) SE-dose-dependent reductions in body weight with increased mortality and lesions in the eye, heart, and thymus were found in the 5-FU-treated birds versus the control birds. Alternatively, the control birds had significantly more intestinal lesions than the 5-FU-treated birds. No consistent significant hepatic lesions were observed in either treatment group. Under the conditions used in these experiments, 5-FU treatment of chickens caused otherwise subclinical SE infections to rapidly become clinical infections with more severe extraintestinal organ infections, whereas the control chickens had infections that were primarily restricted to the intestine. These findings suggest that the heterophil is extremely important in controlling both initial SE organ invasion and subsequent disease pathogenesis in chickens.