It was noted that the punctate immunostaining for MSA-1 was accompanied by sparse CD13 staining and always in juxtaposition to redistributed iDCs. We have previously shown that maturation of splenic iDC from naïve calves in vitro results in the loss of CD13 expression and gain in capacity to present antigen (12,41). Thus, similar to the P. chabaudi model in mice (23), these results
support the hypothesis that iDC mature during processing of the parasite and migrate as antigen-presenting cells to lymphocyte-rich domains. The spleen-dependent innate response of naïve find protocol calves to infection with B. bovis is also characterized by early IL-12 production with subsequent IL-10 modulation (6), the major sources of which in cattle are iDCs and monocytes/macrophages, respectively (8,14,42). We have also shown that monocytes/macrophages of cattle can produce NO with direct babesiacidal activity (14,27,43). It was interesting to note that following haemoparasitic infection, intense acute hyperplasia of monocytes/macrophages is restricted to the red pulp of both mice (23) and calves (present study). Thus, in addition to regulatory function through cytokine production, our collective findings are consistent with monocytes/macrophages acting as effector cells in close juxtaposition with infected erythrocytes as they enter
the splenic sinuses. Regarding the distribution of small leucocytes, dual-labelling experiments demonstrated acute progressive accumulation of numerous CD3+ CD4− cells and TcR1+ WC1− cells within the red Smoothened Agonist datasheet pulp. Thus, it is likely that at least a portion of these accumulated Methane monooxygenase lymphocytes were WC1−γδ T cells. The role of these cells is still not clear but as bovine WC1−γδ T cells express CD2 and CD8, can produce
IFN-γ in response to cytokine stimulation, and are found in largest proportion in the spleen and intestine (15,16,44,45), it is intriguing to consider the possibility that cells with this phenotype might be the bovine functional equivalent of NKT cells (46–48). If so, then the observed accumulation of these cells in the red pulp of naïve calves infected with B. bovis is consistent with their expected role in the transition from innate to acquired immunity. Our results are in agreement with previous reports (49,50) that demonstrate relatively small accumulations of WC1+γδ T cells within the splenic marginal zones of uninfected calves. The splenic decrease in WC1+γδ T cells during the acute response of calves to B. bovis infection may indicate their activation within the marginal zone is followed by redistribution to effector sites outside of the spleen. Indeed, several reports indicate WC1+γδ T cells are most numerous and reactive within the blood of young calves (45,49,51–53).