Macrophage recruitment and activation: a model for comparing resistance toSalmonella Enteritidis in different broiler breeds

A model for comparing resistance to Salmonella Enteritidis was evaluated in different broiler breeds. The recruitment and phagocytic activity of perit oneal macrophages were assessed in three different broiler breeds (A, B and C) which are farmed world-wide. Assessment was performed after three days of intraperitoneal (i.p.) administration of 3% Sephadex G-200 (10 mi), init iated at twenty-one days of age, followed by contact with i.p, live S. Ente ritidis (10 mi, 1.2 x 10(8) colony forming units/ml) for 45 min. Assessment included determination of the number of i.p. macrophages recruited, the nu mber of i.p. phagocytised S. Enteritidis cells per macrophage, the levels o f degranulated i.p. beta -glucuronidase and beta -galactosidase, and the co unt of surviving S. Enteritidis cells. Confirmation of the significance of the model was obtained by comparing resistance to field infection by S. Ent eritidis in the three broiler breeds. The recruitment of i.p. macrophages in response to challenge with Sephadex and S. Enteritidis was significantly higher (P < 0.05) in birds of breed A (mean cumulative i.p. macrophage count, in 10 fields of microscopic slide s mear magnified at x 1,000, was equal to 81.7), compared to recruitment in b irds of breed B (33.3) or breed C (41.2). The mean number of phagocytised S . Enteritidis cells per i.p. macrophage in birds of breed A (2.68) was sign ificantly higher (P < 0.05) than in breed B (0.83) and insignificantly high er (P>0.05) than in breed C (2.35). In addition,the highest level of recrui tment and phagocytic activity of macrophages, in birds of breed A, was asso ciated with a higher significant mean i.p. P-glucuronidase activity (10,425 .5 units/ml) than in breed B (3,438.2 units/ml) or breed C (3,356.94 units/ ml) (P < 0.05). Moreover, birds of breed A demonstrated a higher mean i.p. P-galactosidase activity (2.225 units/ml) than birds of breed B (0.852 unit s/ml) or breed C (1.852 units/ml) (P > 0.05). The higher level of recruitment and activity of i.p. macrophages a nd the h igher rate of degranulation of i.p. enzymes in breed A were associated with a greater number of surviving i.p. S. Enteritidis cells. In response to ou tbreaks of S. Enteritidis in the field, the average mortality was significa ntly higher in flocks of breed A (3.2%) than in flocks of breed B (1.2%) or breed C (0.96%) (P < 0.05). These data provide an indication of the signif icance of the model in reflecting the differences in resistance to S. Enter itidis of broiler breeds reared in a farm environment.