Oral inoculation of foals with virulent Rhodococcus equi bacteria

Oral inoculation of foals with virulent Rhodococcus equi bacteria demonstrated accelerated cytotoxic T lymphocyte development and IFN-�� production [24]. In sheep, Emery et al. determined that lambs repeatedly infected with infectious larvae of Haemonchus controtus or Trichostronglyus colubrifomis starting from the then day of birth for 4�C6 weeks showed significant reduction in mean faecal egg count compared to control lambs [25,26]. Importantly, the cell-mediated immune responses (i.e. antigen-specific cellular proliferative response and IFN�� production) by trickle-immunised lambs was not significantly greater than that in control animals, which corroborates our CMI response [25]. Although at least 50% of all vaccinated animals some induction of IFN�� compared to media controls, the level of response was very low (Figure 3A) and no proliferative response was observed (Figure 3B).

Emery et al. also show that lambs were protected despite no significant increase in serum antibody production [25]. When they repeated their trial to include lambs repeatedly infected with infectious T. colubrifomi larvae, only animals also immunised i.p. with 50 ��g of the recombinant T. colubriformis derived protein in the presence of IFA showed induction of IgG1 and IgG2 isotypes antibody secreting cells in mesenteric lymph nodes [26]. In contrast, data from our study showed significant induction of OVA-specific serum IgG prior to and post i.p. immunization (Figure 1A-C) and significant mucosal IgA but not IgG was induced after i.p. immunization (Figure 2A, B). Experiments by Mutwiri et al.

(2001) determined that consistent exposure of a localized region of the newborn GALT to antigen was sufficient to promote mucosal and systemic immunity [15]. Specifically, they localized adenovirus coding for TgD antigen to a segment of the newborn gut. They presumed that antigen would be consistently expressed (although the levels and duration of expression were not assessed [27]). While their results were intriguing, antigen in this study was introduced to the gut with several potentially confounding factors. Because the immunized intestinal ��loops�� were created in fetal lambs at late gestation and the ��loops�� were made to be sterile, the antigen was not diluted out by the presence of commensal flora.

Further, because the ��loops�� were removed from the active digestive tract (while still keeping lymphatics, enervation and blood flow intact), antigen was not influenced by the potentially inhibitory factors present in colostrum and milk and the peristaltic action of the gut. Regardless, these experiments showed that antigen Anacetrapib alone (or at least one coded for by adenovirus) introduced to a localized region of a sterile gut could promote mucosal and systemic immunity in newborn lambs.

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