Heterophils and Macrophage-Like Cells in the Caeca Chicks’ Caeca after Experimental Infection with Salmonella enteritidis PT4

Abstract

In order to study the interaction between heterophils and monocyte-macrophage system cells with salmonella, one-day-old White Plymouth Rock chicks were inoculated with 2 × 10 8 colony forming unit (CFU) of Salmonella enteritidis phage type 4. Samples from the caeca were taken for light and electron microscopy study.Groups of birds were euthanized by cervical dislocation at 6 hours (h) post inoculation and after 3, and 10 days (d) post inoculation. Histological examination at 3 d after infection showed heterophilic and mononuclear infiltration into the lamina propria mucosae and tela submucosa. The accumulation of macrophage-like cells accompanied this process at 10 d after infection. Electron microscopy revealed the presence of heterophils in the lamina propria at 3 d after infection and their migration between mucosal epithelial cells to intestinal lumen at 10 d after infection. Some of them were smaller with gap formation between intercellular space and heterophils. There was a decrease of the number of specific granules inside. Bacteria were not found within their cytoplasm. Oedema, condensation of chromatin, disruption of nuclear membrane and degradation of cytoplasmic organelles were seen in macrophage-like cells in the lamina propria. Formations of intracellular inclusions with cytoplasmic organelles and bacteria in various stages of degeneration were also observed in these cells. The cytoplasmic membrane was not disrupted.Our results showed that infection of one-day-old chickens with Salmonella enteritidis PT4 caused the interepithelial accumulation of heterophils. The observed morphological changes of heterophils indicated their degranulation. It seems to be caused by the release of antimicrobial peptides.Intracellular changes of monocyte-macrophage system cells without any injury of their cytoplasmic membrane show their survival of the Salmonella enteritidis PT4 infection. We suppose the rupture of their cell membrane in the later stage and the release of dead material with bacteria into the surrounding. In this way the monocyte-macrophage system cells serves in this condition as a vehicle and source of later infection.