Expression of Immune Genes and Leukocyte Population in the Conjunctiva, Harderian Gland and Trachea of Chickens Inoculated with a Live Vaccine and a Field Strain Infectious Laryngotracheitis Virus

Changes in leukocyte populations and immune gene expression associated with attenuated vaccine (SA2) or field (Class 9) strains of infectious laryngotracheitis virus in chicken pullets were observed primarily in the trachea and conjunctiva, while no substantial changes were detected in the Harderian gland. Although there were no significant differences in cellular infiltration in the tissues exposed to Class 9 and SA2, Class 9 induced greater changes in immune gene expression than SA2 in the trachea and conjunctiva and significantly upregulated CD4, CD8A, IRF1, STAT4 and downregulated CXCL12 expression in the trachea. Meanwhile, SA2 significantly upregulated CD14 and downregulated MPO, CCR6 and RAG1 expression in the conjunctiva. In conclusion, gene expression in pullets infected with SA2 and Class 9 were mostly related to inflammatory and tissue-repairing responses in the trachea and conjunctiva. Compared to SA2, Class 9 inoculation was associated with a more robust gene expression of immune markers; however, a larger infiltration of Kul01+, Bu1+ and CD8a+ cells was observed in trachea and conjunctiva after SA2 inoculation. © 2024 by the authors.