INDUCTION OF CD4(-CELL RESPONSES IN EFFERENT LYMPH RESPONDING TO TOXOPLASMA-GONDII INFECTION - ANALYSIS OF PHENOTYPE AND FUNCTION() AND CD8(+) T)

The kinetics of induction of T cell responses were examined in efferen t lymph from a node draining the site of a primary inoculation of Toxo plasma gondii. The numbers of T cells increased after infection, due i nitially to an expansion of the CD4(+) T cell population followed by a n increase in the number of CD8(+) T cells which coincided with the pe ak lymphoblast response. Proliferative responses of CD4(+) T cells to T. gondii antigen were detectable from day six after infection and imm une efferent lymph cells inhibited the intracellular multiplication of T. gondii in vitro. Optimum inhibition was achieved using CD8(+) T ce lls restimulated in vitro, and the effector function appeared to be di rected preferentially against the autologous rather than the allogenei c infected target cell. The results provide unique information on the induction of immune responses to T. gondii in vivo and provide evidenc e that both CD4(+) and CD8(+) T cells are necessary for the developmen t of protective immunity induced by the S48 strain of T. gondii which is used as a live vaccine in sheep.