ABSTRACT:The aim of this study was to evaluate the effects of immunising farm animals with the Histophilus somni recombinant heat shock protein 60kDa (H. somni rHsp60) in field conditions. Fifty piglets, 10 calves and 30 hens were immunised twice, and the same number of each species was used as the control. The humoral immune response was evaluated using ELISA in piglets (IgG, IgA and IgM) and calves (IgG 1 , IgG 2 and IgM) sera and in hen egg yolks (IgY). Cell-mediated immune responses were evaluated using the skin test. Concentrations of serum haptoglobin in calves and piglets and plasma fibrinogen in calves, daily weight gain in piglets, as well as the inner body temperature and clinical signs in calves were measured to evaluate the clinical effects of vaccination. In animals immunised twice with H. somni rHsp60, a statistically significant increase in IgY antibodies in egg yolk as well as serum IgG 1 and IgG 2 antibodies in calves (P < 0.05) was found. In piglets, the antibody reaction against H. somni rHsp60 was higher in the experimental than in the control group, but the difference was significant only for the IgG class (P < 0.05). A moderate cell-mediated immune response to H. somni rHsp60 measured using the skin test was observed in piglets after 24 h (P < 0.05), but not in calves and hens. The daily weight gain was significantly higher in the experimental than in the control piglets (P < 0.05). The fibrinogen and haptoglobin levels in calves, as well as the inner body temperature, indicated a reduced risk of pathology in the experimental group of calves. The preliminary results confirmed the immunogenicity of H. somni rHsp60. A beneficial effect on piglet weight gain was observed. The obtained results warrant further studies of the protective effects of H. somni rHsp60 as an ingredient of subunit vaccines in farm animals.

Background Gram-negative bacterial infections are a serious problem in beef and dairy cattle. Bacterial outer membrane proteins (OMPs) play a pivotal role in cellular survival and the host-bacterium interaction. Histophilus somni OMP40 was identified as a porin with homology between its N-terminal amino acid sequence and the sequences of porins of other gram-negative bacteria The aim of this study was to produce recombinant H. somni OMP40 (rOMP40), optimize its production and evaluate its immunogenic properties in calves. The cross-reactivity of anti-rOMP40 antibodies were also checked. Results The highest overexpression of rOMP40 was demonstrated by Escherichia coli C41 using the autoinduction process. Double immunization of calves (20 μg rOMP40 per animal) induced a significant increase of anti-rOMP40 antibodies in the IgG1 (P ≤ 0.01) and IgG2 (P ≤ 0.01, after first immunization only) subclasses, but not IgM. ELISA revealed increased reactivity of the IgG against surface antigens of E. coli and Pasteurella multocida after the second immunization (P < 0.01). Cross reactivity of anti-rOMP40 antibodies with ~ 40 kDa antigens of most common gram-negative pathogens was shown by Western blotting. Conclusion Immunization with H. somni rOMP40 induced a humoral response in cattle with broad cross-reactivity with similar antigens of other species of Pasteurellaceae and Enterobacteriaceae families and the delayed-type hypersensitivity reaction. The obtained results encourage further study to evaluate the protective effect of the produced protein as a subunit vaccine in cattle.