TNF and infection: While infection with 105 and 106 CFU of cda1Δ2Δ3Δ cells did not elicit significant TNF-α induction, infection with 107 CFU of the cda1Δ2Δ3Δ mutant clearly produced a dramatic spike in its levels in the lung on day 3 p.i. Accordingly, vaccination with 105 and 106 CFU of the cda1Δ2Δ3Δ mutant did not confer any protection.