Lysates of turkey-grown Pasteurella multocida: partial solubilization of the cross-protection factor(s)

A lysate of turkey-grown Pasteurella multocida was treated to determine the nature of a cross-protection factor (CPF). Complete lysate was treated with proteolytic enzymes and mild heat. Cross protection was not induced with pepsin-treated lysate, but 50% cross protection was induced with trypsin-treated lysate and 100% cross protection was induced in turkeys vaccinated with lysate heated at 56 C for 1 hour. Complete lysate was also fractionated by differential and sucrose density gradient centrifugation. After the lysate was centrifuged for 1 hour at 100,000 x g, the CPF was found in the supernatant and pellet fractions, indicating that the CPF was dispersed throughout; 84% of the lysate protein was in the supernatant and 14.7% of the protein in the pellet. After sucrose density gradient centrifugation, 100% cross protection was induced with the top and bottom gradient fractions and 60% with the middle fraction. Although the differential centrifugation pellet and bottom sucrose gradient fraction had protein that was disproportionately small when compared with the soluble portions of the whole lysate, they had the CPF equal in immunizing capacity.