Comparison of immunogenic properties of native and inactivated Mannheimia haemolytica Lkt in calves.

The aim of this study was to compare the immunostimulatory properties of Lkt of M. haemolytica inactivated by formaldehyde and glutaraldehyde and to evaluate the neutralizing properties of anti-Lkt antibodies. The experiment was conducted on 20 Black-and-White Lowland calves of 100 kg body weight, assigned to 4 experimental groups. The animals were given subcutaneous vaccine injections with native Lkt, Lkt inactivated by formaldehyde or Lkt inactivated by glutaraldehyde. The anti-Lkt antibody titres were measured using an enzyme-linked immunosorbent assay (ELISA), based on absorbance of the sera obtained from the animals immunized with the different forms of Lkt. The protective effects of the antibodies present in the sera isolated from the vaccinated animals were estimated using an MTT assay. Analysis of the ELISA absorbance values in the sera from calves in the vaccinated groups did not show any significant differences between the groups. The highest increase in absorbance of sera was observed in calves from the group that received formaldehyde-inactivated Lkt. In the case of calves immunized with native Lkt, the absorbance values were lower than in the group immunized with Lkt inactivated by formaldehyde. The lowest absorbance values were observed in sera obtained from calves vaccinated with Lkt inactivated by glutaraldehyde. Analysis of the MTT assay results revealed the greatest Lkt-neutralizing properties of antibodies in the sera of calves immunized with two doses of a vaccine containing native Lkt and Lkt inactivated with formaldehyde.