The immunoglobulin light chain in poikilothermic vertebrates

The immunoglobulin light chains are classified as κ or δ in mammals and birds (homoeothermic vertebrates), but the traditional criteria for this classification are not applicable to the light chains found in poikilothermic vertebrates. Still it is possible to find some relationships between Ig light chain sequences in these animals and in those of the homoeothermic animals. It is generally accepted that the Ig light chains contribute to the antigen binding capacity of antibodies and the variability is approximately similar in all studied vertebrate species except the elasmobranchs. This might be explained by the organisation of the Ig light chain locus in these animals and the fact that the variable and joining DNA segments are joined in the genome. These conclusions are limited by the small number of species studied in this respect.