Date of Graduation

5-2026

Document Type

Thesis

Degree Name

Bachelor of Science in Agriculture

Degree Level

Undergraduate

Department

Poultry Science

Advisor/Mentor

Gisela, Erf

Committee Member

Dr. Jossie M. Santamaria

Second Committee Member

Dr. Chrysta N. Beck

Abstract

Marek's disease, caused by a herpesvirus, is a major issue in poultry production due to its high mortality rate. The herpesvirus of turkeys (HVT) vaccine has been used as a crucial measure to mitigate outbreaks of Marek's disease in poultry production; however, little is known about the immune response to the HVT vaccine. In this study, we examined how primary and secondary intradermal (i.d.) vaccination with the HVT vaccine in the growing feather (GF) pulp affects local and systemic immune responses, including cellular, antibody, and cytokine responses. Six 9-week-old and six 19-week-old Light-brown Leghorn (LBL) pullets received a primary or secondary HVT vaccination, respectively, by i.d. injection into the GF-pulp (GFs; 10 µL/GF; 16 GFs/pullet). GFs were collected before (0 h) and at 0.25, 1, 2, 3, 5, 7, and 10 d post-pulp-injection (p.i.) and heparinized blood at 0 h and 0.25, 1, 3, 5, 7, 10, 14, 21, 28 d p.i. Leukocyte population profiles in GF-pulps (0 to 10 d p.i.) and blood (0, 6 and 24 h p.i.) were established by immunofluoresecent staining of pulp- and blood-cell suspensions and fluorescence-based flow cytometry analysis. Relative HVT-specific IgM and IgG antibody levels were analyzed by ELISA. Reverse transcription quantitative PCR (RT-qPCR) was used to determine cytokine mRNA expression in the GF-pulps. For statistical data analyses, two-way ANOVA was used for GF leukocyte- and cytokine mRNA-data, and one- or two-way Repeated Measures ANOVAs for blood leukocyte- and plasma HVT antibody-data. For all data, multiple-means comparison analyses were applied as appropriate, and significance was set at P ≤ 0.05. In GF-pulps, V1 and V2 recruited leukocytes, primarily lymphocytes, by 1 d p.i., with peak levels (% pulp cells) exhibited at 3 d p.i., whereby peak leukocyte recruitment was higher with V1 than V2 (54% vs. 24%). Leukocyte levels returned to pre-injection levels at 10 d p.i. for both V1 and V2. Levels of heterophils and macrophages peaked at 0.25 d p.i. with both V1 and V2. B- and T-lymphocyte recruitment was much higher at 3, 5, and 7 d following V1 than V2 vaccination. The V1 T cell response involved primarily CD4+ T cells, with levels elevated from 3 to 10 d p.i., and the V2 T cell response was dominated by CD8+ T cells, with peak levels at 1 and 3 d p.i. Injection of HVT also altered GF-pulp cytokine mRNA expression, with overall higher IL-1β, IL-6, and type I interferon (IFN-α & β) mRNA expression in V1 compared to V2 pullets. For all cytokines, mRNA levels tended to drop during the first days p.i., returning to 0 h levels by 7 d; this suppression was more pronounced with V1 than with V2. In the blood, i.d. V1 and V2 injections increased total WBC, heterophil, and B cell concentrations at 6 h p.i., and V1 pullets had overall higher concentrations of heterophils and T cells than V2 pullets. HVT-specific IgM levels in the plasma were elevated at 10 d and 28 d p.i. in V1 pullets and did not change over 28 d p.i. in V2 pullets, although HVT-IgM levels were already higher at 0 d p.i. with V2 than V1. Plasma HVT-specific IgG steadily increased to highest levels at 28 d p.i. in V1 pullets and increased only slightly over 28 d p.i. in V2 pullets, although HVT-IgG levels were already higher at 0 d p.i. with V2 than with V1. Overall, V1 and V2 resulted in temporal, qualitative, and quantitative differences in leukocyte profiles suggestive of primary and secondary cell-mediated, antiviral immune responses, whereby the cyclic drops in cytokine mRNA expression likely reflect the HVT infection-mediated suppression of inflammatory and antiviral pathways. The robust HVT-specific IgG antibody response to V1 was maintained over time but was not further stimulated by V2, presumably due to the persistence of HVT infection induced by live HVT vaccination on the day of hatch.

Keywords

Tissue and cellular immune responses, systemic immune responses, Herpesvirus of turkeys, Marek's disease, Egg-type chickens, Growing feather bioassay

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