Alteration of protective and serologic responses in BALB/c mice vaccinated with chemically modified versus nonmodified proteins of Brucella abortus 19.

A study was conducted to determine whether the covalent chemical modification of Brucella abortus 19 salt-extractable proteins (BCSP) and BCSP derivatives would modulate the immune responses in BALB/c mice. Salt-extractable proteins BCSP 0-70 and BCSP 70-100 were modified with acetoacetic anhydride, and recombinant proteins rBCSP20 (20 kDa), rBCSP31 (31 kDa), and rBCSP45 (45 kDa) were modified with succinic and dodecanoyl anhydrides. Four weeks after mice were vaccinated with the different preparations, principal and control mice were challenge exposed with a virulent culture of B. abortus 2308, and mice were necropsied 2 weeks later. Serum samples were obtained immediately before mice were challenge exposed and at necropsy. Sera were tested for specific immunoglobulin M (IgM) and G (IgG) antibodies by using an enzyme-linked immunosorbent assay. Acylation decreased the immune responses (increased IgG antibodies and reduced spleen CFU and splenomegaly) induced by both BCSP 0-70 and BCSP 70-100. Modification of the recombinant proteins by dodecanoyl and succinic anhydrides had no effect on the protection induced; however, the IgG serologic responses to the homologous and heterologous proteins were altered. Monophosphoryl lipid A markedly enhanced the immunogenicity of BCSP 0-70.