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Keywords

leukocytes, chickens, lipoteichoic acid, innate immunity, inflammation

Abstract

Lipoteichoic acid (LTA) is a cell-wall polymer in Gram-positive bacteria that stimulates inflammation. Few studies have investigated in vivo immune response to LTA, and none of the in vivo studies have been performed in birds. For this project, the pulp (a skin derivative) of growing feathers (GF) of chickens was used to investigate the in vivo effects of intradermally injected LTA. In Study 1, GF of chickens were injected with 10 μL of differing concentrations of LTA (0.1, 1.0, 10, 100 or 250 μg LTA/mL; 3 chickens/dose). Growing feathers were plucked before injection (0 h) and at 6, 24, 48, and 72 h post-injection and frozen before staining using immunohistochemistry for visual inspection of leukocyte infiltration. Ten μg/mL LTA was found to be the optimal concentration to stimulate inflammation. In Study 2, GF were injected with 10 μL of either 10 μg/mL LTA (0.1 μg LTA/GF, 12 GF/bird, n = 8) or PBS (vehicle; n = 4). GF were collected at 0, 6, 24, 48, and 72 h. For each time point, pulp cell suspensions were prepared and immunofluorescently stained with a panel of chicken-leukocyte-specific monoclonal antibodies. Cell populations were analyzed via flow cytometry, revealing elevated levels (% pulp cells) in total leukocytes, monocytes/macrophages, and major histocompatibility complex (MHC) class-II expressing cells in GF injected with LTA when compared to the control. Infiltration of lymphocytes and heterophils was not different between treatment groups. This study suggests that the inflammatory response to LTA in chickens is characterized primarily by recruitment of monocytes/macrophages to the site of inflammation.

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