Unveiling the immunomodulatory role of soluble chicken fractalkine: Insights from functional characterization and pathway activation analyses

This study describes the first successful cloning and functional characterization of chicken CX3CL1, a chemokine involved in immune cell migration and inflammatory responses. Evolutionary analyses revealed its close relation to CX3CL1 from other avian species, particularly duck, turkey, and quail. Structurally, chicken CX3CL1 includes a signal peptide and a chemokine interleukin-8-like domain characterized by unique alpha-helices and disulfide bonds. Additionally, we produced and purified recombinant CX3CL1 protein and assessed its endotoxin levels. Chemotaxis assays revealed that CX3CL1 significantly enhances the migration of HD11 macrophages and CU91 T cells. Furthermore, recombinant CX3CL1 induced the expression of pro-inflammatory cytokines (TNF-α, IFN-β, IFN-γ, IL-6, and CCL20) in a time-dependent manner, while exerting differential effects on anti-inflammatory cytokines (IL-4, IL-10). Conversely, transfection with siCX3CL1 or siCX3CR1 led to the downregulation of these responses. We also observed activation of the MAPK, NF-κB, and JAK/STAT pathways, evidenced by increased phosphorylation of key signaling molecules. These findings underscore the crucial role of chicken CX3CL1 in regulating immune responses, cell migration, and the activation of key signaling pathways. This study provides valuable insights into the immunomodulatory functions of soluble CX3CL1, highlighting its potential as a therapeutic target for inflammatory conditions and enhancing our understanding of immune cell dynamics.