A functional interleukin-4 virokine is encoded within the genome of infectious laryngotracheitis virus: unveiling a novel virulence factor

Authors: VOLKENING, JEREMY - Base2bio; Spatz, Stephen; GARCIA, MARICARMEN - University Of Georgia; Ross, Teresa; MAEKAWA, DANIEL - Merck Animal Health; ROSENTHAL, KENNETH - University Of Georgia; ZAMORA, ANA - University Of Georgia; SKIPPER, APRIL - University Of Georgia; Blakey, Julia; PAUDEL, ROSHAN - University Of Georgia

Submitted to: PLoS Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: This study investigates the immune evasion strategies of the herpesvirus infectious laryngotracheitis virus, an important pathogen of poultry. The manuscript focuses on the acquisition of a host cytokine gene into the genome of an avian dinosaur virus some 65-70 million years ago. The virus integrated functional copies of a gene that encoded a protein to an important cytokine known as interleukin 4. This viral encoded cytokine or virokine is postulated to disrupt the normal cytokine signaling pathways of the host, manipulating the immune response to favor viral persistence.The research highlights the discovery of a previously unknown virokine in a bird virus. This virokine shares significant structural and functional homology with vertebrate interleukin-4 (IL-4). It was found to stimulate nitric oxide production in macrophages, similar to authentic chicken IL-4. However, unlike the genuine molecule, this viral mimic weakens the bird's immune response. Further evidence supporting its role in virulence comes from studies where the virokine gene was deleted from the virus. Birds infected with this modified virus exhibited reduced disease severity compared to those infected with the wild-type virus.These findings provide a deeper understanding of how herpesviruses manipulate the immune system through virokines. This knowledge is crucial in developing novel therapeutic strategies to combat herpesvirus infections.

Technical Abstract: Herpesviruses have evolved numerous immune evasion tactics, persisting within their hosts through self-perpetuating strategies. One such tactic involves acquiring functional copies of host genes encoding cytokines such as Il-6 (HHV-8), IL-8 (GaHV-2), IL-10 (HHV-4, HHV-5), and IL-17 (SaHV-2). These viral mimics, or virokines, can bind to cellular receptors, modulating the natural cytokine signaling and manipulating the immune response to favor the virus. In the course of full-length cDNA sequencing of infectious laryngotracheitis virus transcripts, a previously unknown highly spliced gene was discovered in the viral genome predicted to encode a 147 amino acid protein with similarity to vertebrate interleukin 4. The three-intron genomic structure was precisely conserved with chicken and other vertebrate IL-4 homologs, and the amino acid sequence displayed structural conservation with vertebrate homologs at the primary, secondary, and tertiary levels based on computational modeling. The viral IL-4 gene was subsequently identified in all sequenced ILTV genomes. Phylogenetic analyses, along with the conserved gene structure, suggested direct capture from a Galliformes host. Functionally, an LPS-stimulation assay showed that the expressed viral IL-4 homolog stimulated nitric oxide production in a macrophage cell line at comparable levels to recombinant chicken IL-4. A recombinant virus lacking vIL-4 exhibited slightly higher titers in cell culture compared to the parental strain. In vivo bird studies demonstrated reduced pathogenicity of the vIL-4 knockout compared to wildtype. These results represent the first report of a previously unknown virokine encoded in the Il-IV genome expressing a functional IL-4homolog and virulence factor.