Ontogeny of heterophil function in neonatal chicks by administration of Salmonella enteritidis-immune lymphokines

Abstract

A granulocytopenic chicken model in more mature birds hics. demonstrated the significant role heterophils have in the defense mechanism against Salmonella. Heterophils from 3-5 week-old chickens have been shown to be highly efficient at phagocytizing and killing Salmonella when compared to monocytes. The purpose of the following experiments was threefold. First, 1 investigated the phagocytic and bactericidal activities of heterophils from chickens during the first 7 days post-hatch to evaluate whether decreased heterophil function plays a role in the susceptibility of young chicks to Salmonella infections. Results demonstrated the ability of the heterophil to phagocytose Salmonella enteritidis did not change on Day 1 or Day 4, but then doubled by Day 7. Bactericidal activity of the heterophils throughout the first 7 days post-hatch demonstrated efficient killing of Salmonella enteritidis. Based on this data, l concluded a relationship exists between the age of the chick, the functional activity of the heterophil, and the susceptibility to organ invasion by Salmonella. Secondly, immunoprophylactic administration of Salmonella enteritidis-immune lymphokines (ILK) in day-old chicks results in both significant reduction in SE organ invasion and enhanced activation of heterophils. Therefore, I evaluated the effects of ILK on the ontogenesis of heterophil phagocytosis and bacterial killing. Administration of ILK induced a significant increase 7<0.05) in heterophil phagocytosis when injected on either day 1, 4, or 7 post-hatch as compared to control chicks of the same age. Thus, administration of ILK to chicks during the first week of life increases functional development and potentiates heterophil biological activity during the greatest period of susceptibility to Salmonella invasion. Thirdly, 1 evaluated the duration of enhanced heterophil phagocytosis of SE following the prophylactic administration of a single injection of ILK to neonatal chicks. Administration of ILK at day-of-hatch resulted in a significant increase in heterophil phagocytic acclivity 7<0.05) through day 5 post-hatch. No significant differences in phagocytic activities of heterophils from control and ILK treated chicks was demonstrated from day 6 through 14 post-hatch. These data suggest that the administration of ILK on day-of-hatch potentiates heterophil phagocytic activity during a critical period of susceptibility to Salmonella infection in neonatal chicks.