Abstract
Infectious laryngotracheitis (ILT) is an acute respiratory disease of poultry caused by infectious laryngotracheitis virus (ILTV). Control of the disease with live attenuated vaccines administered via eye drop build upon immune responses generated by the eye-associated lymphoid tissues. The aim of this study was to assess cytokine and lymphocyte changes in the conjunctiva-associated lymphoid tissues (CALT) and Harderian gland (HG) stimulated by the ocular inoculation of the ILTV chicken embryo origin (CEO) vaccine strain and virulent strain 63140. This study offers strong evidence to support the roles that the CALT and HG play in the development of protective ILTV immune responses. It supports the premise that ILTV-mediated immunomodulation favors the B cell response over those of T cells. Further, it provides evidence that expansions of CD8α+ cells, with the concomitant expression of the Granzyme A gene, are key to reducing viral genomes in the CALT and halting ILTV cytolytic replication in the conjunctiva. Ultimately, this study revealed that the early upregulation of interleukin (IL)-12p40 and Interferon (IFN)-γ cytokine genes, which shape the antigen-specific cell-mediated immune responses, retarded the decline of virus replication, and enhanced the development of lesions in the conjunctiva epithelium.
Highlights
Infectious laryngotracheitis (ILT) is a highly contagious acute respiratory disease of chickens caused by the avian alphaherpesvirus, Gallid alpha herpesvirus 1 (GaHV-1), commonly known as infectious laryngotracheitis virus (ILTV)
From 4 to 7 days post-inoculation, mortalities were not recorded, the group of chickens inoculated with the 63140 virulent strain showed markedly higher clinical sign scores than chickens inoculated with the chicken embryo origin (CEO) vaccine strain (Figure 2a)
The CEO (5.3 log10) and 63140 (4.19 log10) mean genome load peaked in the Harderian gland (HG) at 3 dpi, began declining at 5 dpi, and genomes were eliminated by 7 dpi
Summary
Infectious laryngotracheitis (ILT) is a highly contagious acute respiratory disease of chickens caused by the avian alphaherpesvirus, Gallid alpha herpesvirus 1 (GaHV-1), commonly known as infectious laryngotracheitis virus (ILTV). Intervention strategies to control the disease rely on the implementation of biosecurity measures and vaccination with live-attenuated and/or recombinant viral vector vaccines expressing ILTV proteins [1]. Among live-attenuated vaccines, there are two main types: the tissue culture origin (TCO) vaccine [2] and chicken embryo origin (CEO). CEO and TCO vaccines can be administered through the ocular, oral or intranasal mucosal routes to elicit local and systemic immunity [4,5], are capable of protecting chickens against clinical signs and mortality, and suppress replication of the challenge virus [6]. It has been demonstrated that live attenuated vaccine strains, most commonly the CEO vaccine strains, can revert to virulence if allowed to circulate in naïve chickens and give rise to outbreak viruses, such as the virulent strain 63140 [1]. Live attenuated vaccines are routinely used in the field, there is little definitive knowledge about the molecular and cellular immune response associated with ocular vaccine-induced protection
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