Pathogenic neisseriae--a model of bacterial virulence and genetic flexibility

Generation of antiserum to specific epitopes

The ability to prevent disease by immunization with subunit vaccines that incorporate specific epitopes was demonstrated by DiMarchi et al. (1), who used a synthetic peptide to protect cattle against foot-and-mouth disease. However, generation of antibody to peptide antigens is often difficult owing to the small molecular mass and limited chemical complexity. We tested the hypothesis that recombinant DNA and synthetic peptide techniques would make it possible to stimulate vigorous immune responses to specific epitopes of an outer membrane protein of Neisseria gonorrhoeae. The MtrC AP1 sequence from the invariant MtrC gonococcal lipoprotein was genetically fused to maltose binding protein. The resultant fusion protein was used as the primary immunogen to stimulate MtrC AP1-specific antiserum. To enhance antibody production specific to MtrC AP1, boosting immunizations were performed with synthetic MtrC AP1 sequence contained in a multiple antigenic peptide system immunogen. The MtrC AP1-specific antiserum strongly recognized the MtrC protein on Western blots and appeared to bind native MtrC protein in situ. The generation of antibody in this fashion provides the technology to produce antibody to defined epitopes of any protein, including those found in the gonococcal outer membrane. The ability of those antibodies to inhibit bacterial growth or to activate complement protein can then be tested.

Structural characterization of the lipid A component of pathogenic Neisseria meningitidis

The lipid A component of meningococcal lipopolysaccharide was structurally characterized by using chemical modification methods, methylation analysis, 31P nuclear magnetic resonance, and laser desorption mass spectroscopy. It was shown that Neisseria meningitidis lipid A consists of a 1,4'-bisphosphorylated beta(1'----6)-linked D-glucosamine disaccharide (lipid A backbone), both phosphate groups being largely replaced by O-phosphorylethanolamine. This disaccharide harbors two nonsubstituted hydroxyl groups at positions 4 and 6', the latter representing the attachment site of the oligosaccharide portion in lipopolysaccharide. In addition, it is substituted by up to six fatty acid residues. In the major lipid A component, representing a hexaacyl species, the hydroxyl groups at positions 3 and 3' carry (R)-3-hydroxydodecanoic acid [12:0(3-OH)], whereas the amino groups at positions 2 and 2' are substituted by (R)-3-(dodecanoyloxy)tetradecanoic acid [3-O(12:0)-14:0]. A minor portion was present as a tetraacyl lipid A component lacking either dodecanoic acid (12:0) or 12:0 and 12:0(3-OH). N. meningitidis lipid A, therefore, significantly differs from Escherichia coli lipid A by the nature and locations of fatty acids and the substitution of O-phosphorylethanolamine for the nonglycosyl (4'-P) and glycosyl phosphate.