Evolution of the Lymphocyte

Invertebrates probably lack the cellular and molecular apparatus that characterizes vertebrate immunity but do have their own distinctive defense mechanisms (perhaps best termed 'quasi-immunity') worth investigation in their own right. Investigations of lymphocytes-like cells and immunity in animals near the transition point betweem invertebrates and vertebrates (e.g. the protochordates) may yet yield information on the early development of true vertebrate immunity. In this article Gregoru Warr discusses what light phylogenetic studies throw on the development of immunologically competent cells.