bovis into 6 month-old naïve Holstein calves consistently induced fever (>39·5°C) between 8 and 10 dpi. The rare presence of B. bovis-infected erythrocytes was noted in each animal by examination selleck of Giemsa stained blood films just prior to euthanasia. Although calves were necropsied at different intervals, each was experiencing a decrease in haematocrit from their normal pre-infection levels. At 7 dpi the haematocrit was decreased 19% and by 13–14 dpi had decreased 45 ± 6·7% (n = 3). The spleen of naïve calves doubled in volume by 11–12 dpi and was associated with significant increases in the total splenic content

of small leucocytes (approximately twofold), large leucocytes (approximately eightfold) and total leucocytes (approximately twofold) (Table 2). As determined by FACS analysis (data not shown), the large leucocyte population included monocytes, macrophages, dendritic cells (DCs) (12) and large granular natural killer (NK) cells (15). As viewed in H&E sections, splenomegaly 7–14 dpi was associated with a progressive basophilic hyperplasia within the red pulp and histological reduction in the white pulp (w) and trabeculae (t) elements (Figure 1, 1·25×), and also

a loss in zonal distinction between marginal zone and red pulp (Figure 1, 10×). The regional distributions of phenotyped cells were further investigated by IHC. Examples of the splenic cellular immunoreactivity to monoclonal antibodies specific for Compound Library high throughput CD3 and CD4 are shown in Figure 2a–f. Two cell populations were clearly evident in this dual-labelling experiment:

CD3+/CD4+ and CD3+/CD4− cells. In the uninfected Adenosine triphosphate calf, CD3+/CD4+ cells were always most dense within the periarteriolar lymphatic sheath (PALS; see ‘[’ in Figure 2a,d). A band of CD3+/CD4+ and CD3+/CD4− cells was consistently present within the marginal zones of uninfected spleens, extending 185 ± 29 μm away from the follicle [see ‘{’ in Figure 2a,d]. Both populations were relatively scarce within the red pulp. During the acute response to infection, the distinctive presence of this marginal zone band was obscured by a progressive red pulp increase in CD3+/CD4− cells and a more modest increase in CD3+/CD4+ cells (Figure 2b,c,e,f). The localization of γδ T cells in the spleen is shown in Figure 2g–l. Two major γδ T-cell phenotypes were observed in this dual-labelling experiment: TcR1+ cells that were either WC1+ or WC1−. WC1+ cells were generally small and round in appearance whereas WC1− cells were larger angular cells. In the uninfected calf, WC1+ cells densely populated the marginal zone (900–2500 cells/mm2, see ‘{’ in Figure 2j) but were relatively scarce in the red pulp (100–150 cells/mm2) whereas brightly fluorescent TcR1+/WC1− cells were predominately observed within the red pulp, often appearing clustered (see arrow, Figure 2g).