Printed in Great Britain Cytodynamics and ontogeny of the immune reponse of Xenopus laevis against sheep erythrocytes

The heterologous red cell response of Xenopus laevis larvae and post-metamorphic toadlets was investigated by means of the immuno-cytoadherence (ICA) technique. Sheep erythrocytes (SRBC) were employed as immunogen. Toadlets responded to a single injection of immunogen within 4 days, and exhibited a peak level of rosette-forming cells (RFC) in their spleens at 8 days post-injection. Toadlets immunized against sheep erythrocytes gave only a very slight response when tested against rat erythrocytes. A secondary response, much greater in magnitude than the primary re-sponse, wasevidentwithin 2days when previously immunized toadlets were reinjected with the same immunogen. It was concluded that the ICA technique provides a quantitative measure of an acute immune response in these animals. Larvae which had passed through stage 50 of Nieuwkoop & Faber exhibited substantial increases in RFC in the spleens when tested 6-10 days after injection with sheep erythrocytes. Significantly increased frequencies of RFC in thymi were also noted in these larvae, but the numbers involved were very low and varied considerably. Histological observations of these larvae revealed lymphoid maturation of the spleens and thymi to be essentially complete. Larvae which had not reached stage 50 according to external morphological criteria, but whose lymphoid organs had matured to a degree equivalent to stage 50, also exhibited strong anti-SRBC response in the spleens. Response in the thymi was low and not statistically signifi-cant. Larvae injected at a stage when lymphocytic differentiation was complete in the thymi but had not begun in the spleens did not exhibit an elevated splenic RFC frequency when tested after the spleens had matured. These data suggest that the heterologous red cell response in the larval spleen is dependent upon antigenic challenge to spleens which have reached the stage 50 equivalent in their histogenesis