IL-2 released from bovine PPD-stimulated peripheral blood cultures from animals vaccinated with high-dose CFP–IL-2 (▴), low-dose CFP–IL-2 (■), BCG (●), or adjuvant alone (⧫) and challenged with virulent M. bovis at 13 weeks after initial vaccination (experiment 3). Data are expressed as mean stimulation indices and SE. ∗, means were significantly different from the means of the adjuvant control group (P < 0.05). V, vaccination; C, challenge.