Stronger In Vitro Phagocytosis by Monocytes-Macrophages Is Indicative of Greater Pathogen Clearance and Antibody Levels In Vivo

Monocytes-macrophages are crucial play- ers in specific and nonspecific immune responses to protect organisms from invasion of bacteria or viruses. In this study, monocytes in circulation from 2 lines of Silky and Starbro chickens with different disease resis- tance were separated and cultured in vitro. After iden- tification with acridine orange (AO), Giemsa staining, and CD14 immunostaining, monocytes-macrophages were used for adherence and phagocytosis test. The overall percentages of adherence of Silky monocytes was 1.5 times greater than that of Starbro (P < 0.01), which were 26.85% ± 8.24% and 18.34% ± 8.15%, re- spectively (mean ± SD). The monocytes-macrophages phagocytic index, phagocytic product, and percentage of phagocytosis in Silkies were greater than in Star- bros, respectively. The difference of phagocytic index was significant (P < 0.05), that is, 3.70 ± 1.75 and 1.97 ± 0.31, respectively (mean ± SD). Then, 20 Silkies were divided into 2 groups according to phagocytic index: high phagocytic index (HPI) group and low phagocytic index (LPI) group, to study the relationship between phagocytic activity in vitro and pathogen clearance. Af- ter being challenged against Salmonella Pullorum C79- 13, the Silky birds with HPI produced a 3-fold greater level of specific antibodies compared with those with LPI (P < 0.01), 50.21 ± 6.67 and 16.85 ± 4.52, respec- tively (mean ± SD). In contrast to LPI birds, HPI birds shed less Salmonella Pullorum bacteria (P < 0.05), that is, 168.98 × 10 8 ± 294.74 × 10 8 compared to 385.40 × 10 8 ± 399.94 × 10 8 (mean ± SD), and the shedding peak of Salmonella Pullorum in the test span appeared 4 d earlier. These results indicated that phagocytosis of monocytes-macrophages had strong effects on antibody titer and bacteria shedding postchallenge, which could be used to predict the disease resistance in animals.