Humoral and Cellular Immune Responses in Turkey Poults Infected with Turkey Coronavirus

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Abstract
The objective of the present study was to elucidate the kinetics of humoral and cellular immune responses of turkey poults infected with turkey coronavirus (TCV). Turkey poults were orally inoculated with TCV at 10 d of age, and the immune responses were analyzed at 1, 3, 7, 14, 21, 28, 42, and 63 d postinfection (PI) in three different experiments. Total Ig to TCV was initially detected at 7 and 14 d PI in Experiments 1 and 3. In addition, Ig gradually increased from 7 to 21 d PI and remained at 80 immunofluroescent antibody assay (IFA) titers or more thereafter. Lymphocyte proliferation responses of spleen cells to concanavalin A were higher in TCV-infected turkeys than in noninfected control turkeys with significant differences (P < 0.05) being noted at 14 and 63 d PI in Experiment 2 and at 3 and 28 d PI in Experiment 3. Strong IFA staining response to TCV antigen was observed in intestines of turkeys at 1, 3, and 7 d PI, and the response declined from 14 to 28 d PI in Experiment 3. In Experiment 3, the IgG isotype antibody response to TCV was markedly increased after 21 d PI and remained high until 63 d PI. The IgM isotype antibody response to TCV was 1.40 and 0.91 at 7 and 14 d PI, respectively. The IgA isotype antibody response to TCV was very low as detected at 7 (0.13), 14 (0.20), and 21 (0.17) d PI. Turkeys infected with TCV had significantly higher (P < 0.05) antibody response to sheep erythrocytes than noninfected controls at 7 d PI. Virus-specific lymphocyte proliferation response of spleen cells was significantly stimulated (P < 0.05) at 63 d PI in Experiment 3. The proportion of the CD4+ subpopulation of T lymphocytes was significantly increased (P < 0.05) at 1, 7, and 21 d PI in Experiment 3. The results indicate that humoral and cellular immunities to TCV are elicited in turkeys following infection with TCV.

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