Generation of immunity against infectious laryngotracheitis virus in chickens

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Live vaccines have been used to control infectious laryngotracheitis virus (ILTV) for over 70 years; however, the mechanisms by which vaccines elicit immunity are poorly understood. Revealing how immunity is formed by different vaccination methods could inform poultry industry practices and assist in the development of safer and more effective vaccines.
The overarching aim of this thesis is to elucidate the immune response associated to ILTV in chickens inoculated by different routes. The specific aims included: 1) Reveal differences in immune gene expression and immune cells profile generated by an Australian ILTV vaccine and a field strain; 2) Elucidate the immune gene expression responses generated by ILTV eye-drop and vent brush vaccination, and 3) Contrast the immune gene expression responses after ILTV inoculation of a vaccine and field strain administered by eye drop and oral routes.
Regarding the first aim, the gene expression in the trachea and conjunctiva of pullets infected with ILTV vaccine (SA2) and field strain (Class 9) were mostly related to inflammatory and tissue-repairing responses. Responses against the ILTV field strain was associated with more robust gene expression of immune markers, associated with upregulation of CD4, CD8A, IRF1 and STAT4, and downregulation of CXCL12 genes in the trachea, compared to the vaccine strain, which was associated with upregulation of CD14 and downregulation of MPO, CCR6 and RAG1 genes in the conjunctiva. However, a larger infiltration of immune cells (KUL01+, Bu1+ and CD8A+) cells was observed in the trachea and conjunctiva after inoculation with the SA2 vaccine than the field strain of ILTV.
Regarding the second aim, there was an increase in gene expression of inflammatory markers in inoculated organs after eye-drop (ED) and vent brush (VB) vaccination. In the vent brush inoculated birds, there was an increased expression of IL6 and IFNG in cloaca at 3 days post inoculation (dpi) and IL2 in conjunctiva at dpi 7 compared to the eye-drop inoculated birds (P<0.05), while there was increased CCL4 expression in conjunctiva at dpi 5 in the eye-drop inoculated group compared to the VB group. The increased expression of IL2 and IL17C associated with the ED vaccination while the increased expression of IL6 and IL17C in trachea associated with VB vaccination. Similarly, ED/VB and VB/ED associated increased IL2, IL6 and IL17C expression in the revaccination sites. In conclusion, the gene expression of immune markers in tissues following the first and second ILTV vaccination using ED and VB were vaccination site specific and associated with inflammatory responses in the inoculated mucosal tissues and in the trachea of inoculated birds.

Notes

Funding SourceRTP, DAP and DVCR scholarships