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The present study was undertaken to establish reference values for the composition of blood leucocyte populations in neonatal calves by differential leucocyte counts and immunophenotyping. Neonatal calves 1 h post partum (p.p.) were found to have a very high absolute number of granulocytes while the number of peripheral blood mononuclear cells was lower than in calves aged 3-9 weeks. The relative numbers of T cell subpopulations were similar in newborn and older calves, but newborn calves had lower percentages of B cells and MHC class II positive cells. Within the first 4 h of life the relative numbers of CD2+, CD6+, and CD8+ T cells declined in colostrum-fed as well as in colostrum-deprived calves. In contrast, the percentage of MHC class II positive cells and monocytes increased from 1 h to 4 h p.p. particularly in colostrum-fed calves. Although there is some evidence for immaturity of lymphocytes in neonatal calves, the immune system of these animals seems to be fully present at birth.

Bacterial lysates of different bacterial strains (E. coli, B. bronchiseptica, P. haemolytica) were prepared by heating, acid- and alkaline-hydrolysis. Lysates were tested for their immunostimulating effect in bacterial infection models and with chromium 51 test demonstrating spontaneous (natural) cytotoxicity. Lysate production was standardized by protein- and Lps-determination. The alkaline-hydrolysis reduced toxicity of Lps and increased the content of soluble bacterial protein. Heating and acid-hydrolysis did not alter bacterial suspensions with respect to Lps-toxicity and protein-content. Mice infected with P. aeruginosa, P. multocida, E. coli and L. monocytogenes (5-10 LD50) had a significantly longer survival time after prophylactic immunostimulation with bacterial lysates than control animals. No protection was observed in immunostimulated mice infected with Erysipelothrix rhusiopathiae. In the Pseudomonas infection model, bacterial lysates prepared by alkaline-hydrolysis had a 10 times higher immunostimulating effect than lysates prepared by acid-hydrolysis or heating. Bacterial lysates stimulated spontaneous cytotoxicity of natural mouse peritoneal killer cells after intraperitoneal application. Whole bacterial lysates had a higher NK-activity as their corresponding purified lipopolysaccharide portion.

Ten splenectomized and non-splenectomized pigs were experimentally infected with E. suis bearing red blood cells in order to determine the antibody response. All animals were monitored for antibody titer by indirect hemagglutination over a period of 80-290 days postinfection. Latent E. suis infection only yielded a detectable antibody titer in one pig. Acutely infected pigs had a titer ranging up to 1:640. Maximum antibody response lasted only 2 months and dropped below the level of detection of our assay within 2 to 3 months. At this time, the clinical symptoms could reappear and antibodies were again detectable. However, no booster effect was observed with this second outbreak. We also determined the antibody frequency in 138 pigs from 16 herds in Southern Germany. Pigs from only 4 out of 6 clinically positive herds had antibody titer against E. suis. 20 out of 78 pigs of the clinical positive herds demonstrated a detectable E. suis antibody titer. In 10 herds that were asymptomatic and presumed uninfected all 80 pigs were serologically negative for E. suis.