Chicken CD4, CD8alphabeta, and CD8alphaalpha T cell co-receptor molecules

Area of Science:

• Immunology
• Evolutionary Biology
• Comparative Genomics

Background:

• CD4 and CD8 T cell co-receptors are critical for adaptive immunity in vertebrates.
• Previous studies suggested conservation of these molecules, but detailed evolutionary insights were lacking.
• Chicken models offer unique opportunities to study T cell receptor evolution.

Purpose of the Study:

• To investigate the evolutionary conservation of CD4, CD8alphaalpha, and CD8alphabeta T cell receptor co-receptor molecules between chickens and mammals.
• To understand the evolutionary pressures shaping CD8alpha and CD8beta in chickens.
• To explore the implications of unique T cell populations in chickens for understanding co-receptor evolution.

Main Methods:

• Utilized monoclonal antibodies and polyclonal antisera against chicken CD8 and CD4 molecules.
• Analyzed established chicken CD8 allotypes and homozygous strains.
• Examined the inheritance patterns of peripheral blood T cell populations (CD4+CD8+, CD4-CD8alphaalpha).

Main Results:

• Demonstrated evolutionary conservation of CD4, CD8alphaalpha, and CD8alphabeta molecules from biochemical structure to function between chickens and mammals.
• Identified extensive CD8alpha polymorphism in chickens, unlike any other species, suggesting differential evolution of CD8alpha and CD8beta.
• Observed a unique inheritance pattern of peripheral blood CD4-CD8alphaalpha T cells in chickens, indicating single-gene control of CD8alpha expression.

Conclusions:

• CD4, CD8alphaalpha, and CD8alphabeta molecules evolved prior to the divergence of avian and mammalian lineages from reptilian ancestors.
• Chicken CD8alpha and CD8beta have evolved under distinct selective pressures.
• Unique T cell populations in chickens provide novel insights into the evolution of T cell co-receptors.