Figure 3.

Cytotoxic activity and interferon-γ (IFN-γ) responses during experimental infection with Mycobacterium bovis. Six calves (no. 4, no. 5, no. 6, no. 7, no. 8 and no. 9) were experimentally infected with M. bovis; during the course of the infection, peripheral blood mononuclear cells (PBMC) were assayed for in vitro cytotoxic responses to M. bovis[mean response ± standard error of the mean (SEM); Fig. 3a), or plasma from whole blood stimulated with bovine purified protein derivative (PPD) was assayed for IFN-γ (mean response ± SEM; Fig. 3b). Cytotoxic activity generated from 6 × 10⁶ PBMC was determined in triplicate using M. bovis-infected (•) or -uninfected (○) macrophage targets. *Significantly different from 0 weeks (preinfection; P < 0·05); †significantly different from week 17 (P < 0·05).