In comparison with adult cattle, we have previously demonstrated that the immune response of calves involves early IL-12 expression with consequent IFN-γ production, a nitric oxide burst and modulation Smad inhibitor by IL-10 (6–9). This age-related immunity is dependent upon cellular events within the spleen as splenectomy of calves renders them equally susceptible (5,10). Our studies have utilized a technique to

marsupialize the spleen of calves (11) so that cells could be acquired for ex vivo analysis (microplate assays and flow cytometry) (12–16). Such analyses have proven valuable in determining the function of various splenic cell phenotypes but lack the ability to place these cell populations within their anatomical context which include the marginal zone, red and white pulp (17). Amongst many factors that comprise an effective immune response to haemoparasitic infection, trafficking and interaction of cells within such domains are central (18). Intravital imaging techniques have been used to dynamically study such factors within

superficial lymphoid organs (19,20) and, to a limited extent, also within deeper structures including this website the spleen of mice (21). But current techniques are not well suited to study the spleen of large mammals because of the limits on depth resolution (22). An approach readily applied to the spleen of large mammals is the serial analysis of the distribution of phenotyped cells in tissue sections. Similar to a recent study on the acute immune response of naïve mice to haemoparasitic infection (23), we have applied this technique to the spleen of naïve calves infected with Babesia bovis. The results document acute change in the distribution of several cells thought to be important to the spleen-dependent response of naïve calves to B. bovis

and serve to underscore common themes in the acute response to haemoparasitic infections. In addition, this is the first documented use of magnetic resonance imagery to measure spleen volume in calves. Twelve Holstein–Friesian steer calves were obtained at 8 weeks of age, vaccinated against pathogenic Clostridium species, castrated and dehorned. All animals were cELISA seronegative for Anaplasma marginale (VMRD, Pullman WA, USA) and B. bovis and B. bigemina (24–26). Chlormezanone The care and use of these calves were approved by the Institutional Animal Care and Use Committee at Washington State University (Pullman, WA, USA). At 12 weeks of age, all calves underwent a surgical procedure to marsupialize the spleen (11). When necessary, spleen cell aspirates were obtained under local lidocaine anaesthesia into 60cc syringes containing ACD and prepared for in vitro studies as previously described (14,27). Ten of the twelve calves were inoculated intravenously with 1 × 105 erythrocytes infected with the T2Bo virulent isolate of B. bovis (7).