FIG. 2.
Ex vivo IFN-γ secretion by spleen or lymph node cells isolated from unvaccinated (vector control) or vaccinated mice after challenge with a high or low dose of parasites. Groups of six BALB/c mice were immunized with L. donovani (Ld) p36(LACK) DNA vaccine or vector control and challenged with either a high dose (1 × 106 metacyclic promastigotes by i.v. or cutaneous [hind footpad] injection) or low dose (2 × 104 metacyclic promastigotes by i.v. injection) of parasites. At either 3 or 30 days postchallenge, the mice were sacrificed and the spleen or draining lymph nodes were harvested. The spleen or lymph node cells were cultured in complete medium in the absence of exogenous antigen stimulation, and the supernatants were collected 72 h later. The concentration of IFN-γ was determined by sandwich ELISA and is shown as the mean and standard error of the mean for the groups of six mice. The data shown are representative of two or three experiments.