FIG. 6.

Frequency of IFN-γ-producing T cells measured by the ELISPOT assay. Splenocytes were isolated from mice immunized with the L. donovani BT1 null mutant 2 weeks postinfection and stimulated with L. donovani promastigotes (white box) or not stimulated (black box) as described in Materials and Methods. Individual IFN-γ-producing cells were detected by direct visualization and are expressed as SFC per 10⁶ splenocytes. The SFC background determined from naive animals (∼20 SFC per million splenocytes) was subtracted.