Previous attempts in this laboratory to recover BCG from cattle following s.c. challenge proved inconsistent. It is thought that following s.c. inoculation mycobacteria would migrate to the lymph node draining the site of inoculation; Ion Channel Ligand Library however, after inoculation, mycobacteria could disperse within the subcutaneous area and it is possible that mycobacteria could migrate to more than one node. By using intranodal inoculation, we have reduced the possibilities of mycobacteria dispersing within the subcutaneous areas and migrating to nodes other than the lymph node injected. To our knowledge, the experiment described in Fig. 1 is the first time in which a time

curve, albeit partial to day 21, on the recovery of BCG from cattle has been reported. Thus, this is the first report for the relatively consistent recovery of BCG from cattle in quantifiable numbers. This protocol was then used to determine whether prior vaccination using SCH727965 order BCG SSI would affect the recovery of BCG after challenge compared to naïve animals in a manner similar to a standard efficacy vaccine test where virulent M. bovis is used for the challenge phase. Given the volume of literature and our previous experience, we decided to use BCG SSI as the test vaccine in these proof-of-principle experiments. We also decided to harvest lymph nodes after 2 and 3 weeks as we reasoned that this would be sufficient time for immune responses induced by

previous vaccination to have an impact on the control of the BCG challenge and would maximise our ability to detect differences between vaccinated and non-vaccinated animals. On a group basis, prior BCG vaccination did reduce the number of mycobacteria recovered from

vaccinated animals compared to non-vaccinated animals. However, from Fig. 4, it is clear that there was animal to animal variation in both vaccinated and naïve animals following inoculation with BCG Tokyo. It is also clear that not all BCG-vaccinated animals were protected to the same extent. It is possible to divide the animals into protected and not-protected by considering all BCG vaccinates with cfu counts lower than the animal presenting the lowest cfu counts in the non-vaccinated group as protected; all other BCG vaccinates could be considered as not protected. Using this criterion, 4/12 animals would have been Thiamine-diphosphate kinase protected by BCG vaccination after 2 weeks; at 3 weeks, 6/12 animals would have been protected. This outcome therefore parallels the outcome of vaccinated animals after challenge with M. bovis, with a proportion of animals presenting with pathology not indistinct from naïve control animals, and another proportion of animals presenting without or with significantly reduced pathology compared to naïve cattle [12] and [13]. It is of interest that intranodal inoculation of naive cattle with BCG induced immune responses to PPD-B as early as one week after injection (week 9 for previously non-vaccinated animals).