FIG. 4.

The mean and standard error of IFN-γ produced in PBMC cultures from vaccinated or nonvaccinated cattle after culture with leptospira antigen (Ag) or medium (Med). PBMC were evaluated at 3 months (A), 4 months (B), 6 months (C), or 7 months (D). The culture supernatants were assessed by ELISA, and the units shown are OD units from an ELISA plate reader using a wavelength of 450 nm. At months 3 and 4, 15 and 20% of the samples, respectively, were beyond the range of the assay. At months 6 and 7, 18 and 68% of the samples, respectively, were beyond the range when tested undiluted; however, dilutions of the supernatants were tested and the OD units were adjusted according to the dilution. At month 6 only vaccinated cattle were sampled. An asterisk indicates a response by the vaccinated group cultured with antigen which is significantly higher than the response by the nonvaccinated cattle at each time point (P < 0.01).