IMMUNOCHEMICAL IDENTIFICATION OF BRUCELLA-ABORTUS LIPOPOLYSACCHARIDE EPITOPES

Sera from Brucella abortus-infected and -vaccinated bovines recognized four lipopolysaccharide (LPS) determinants: two in the O-polysacchari de (A and C), one in the core oligosaccharide from rough Brucella LPS (R), and one in lipid A (LA). From 46 different hybridomas secreting m onoclonal antibodies (MAbs) against various LPS moieties, 9 different specificities were identified. Two epitopes, A and C/Y, were present i n the O-polysaccheride. Two epitopes were found in the core oligosacch aride (R1 and R2) of rough Brucella LPS. MAbs against R1 and R2 epitop es reacted against LPS from different rough Brucella species; however, MAbs directed to the R2 epitope also reacted against enterobacterial LPS from deep rough mutants. Three epitopes (LA1, LA2, and LA3) were l ocated in the lipid A backbone. Different sets of MAbs recognized two epitopes in the lipid A-associated outer membrane protein (LAOmp3-1 an d LAOmp3-2). LPS preparations from smooth brucellae had small amounts of rough-type LPS. Although LPS from rough brucellae did not show smoo th-type LPS in Western blots (immunoblots), two hybridomas generated f rom mice immunized with rough B. abortus produced antibodies against s mooth B. abortus LPS. Results are discussed in relation to the structu re and function of B. abortus LPS and to previous findings on the epit opic density of the molecule.