Ontogeny of con A responsiveness and mixed leucocyte reactivity in the lizard, Chalcides ocellatus

The immune system of phylogenetically key animals will contribute significantly to our understanding of the evolution of immune response in higher vertebrates. Reptiles, being evolutionary precursors of both birds and mammals, represent a pivotal group and thus a study of their immune system is of special significance. Here we described the emergence of T-cell immune capability in the viviparous lizard (Chalcides ocellatus) throughout embryonic development (stages 36-41 of Zada and El Deeb, 1984) and in newborns. The response of embryonic thymocytes (5 X 10(5) cells/ml) to Con A (5 micrograms/ml in culture) was first detected at stages 36-37, increased gradually during successive stages and then declined at birth to yield low responses in newborn lizards. In addition, embryonic thymocytes cultured in two-way MLR, using several combination sets, were significantly responsive at all stages. Our results reveal a degree of immunological T-cell maturation during reptitilian embryonic life which is similar to results in amphibians and mammals, but not clear with respect to fish and birds where comparative information still somewhat limited.