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30:1233-1247. the cases of both OS species, the concentration of inhibiting antigen NECA required to accomplish 50% inhibition of rabbit immunoglobulin binding increased progressively as the inhibiting disaccharide chain length increased from 1 RU through greater than 50 RU. These data suggest that antibodies directed against both of these meningococcal PSs identify conformational epitopes only fully expressed in higher-molecular-weight forms of these antigens. Meningococcal disease, caused by is usually its capsular polysaccharide (CPS), which protects it against complement-mediated bactericidal activity and NECA opsonization (11, 17). Immunity to contamination with many encapsulated bacteria is usually conferred by antibodies to the CPS (7, 18, 26). strains have been classified into at least 13 serogroups on the basis of the immune specificity of the PS capsule (25). Invasive infections are most frequently caused by five of these serogroupsA, B, C, Y, and W-135 (2). The proportion of meningococcal cases in the United States caused by serogroup Y has increased dramatically from 2% during 1989 to 1991 to NECA 37% during 1997 to 2002 (2). Serogroup W-135, spread in association with the Hajj pilgrimage, has caused outbreaks and isolated cases in many countries, including the United States (4, 21). Of all cases of meningococcal disease in the United States among persons older than 11 years of age, 75% are caused by serogroup C, Y, or W-135 (2). The CPSs are made up of either monosaccharides making a homopolymer, or from repeating models (RU) normally consisting of two to six sugar residues (30). CPSs vary significantly in their ability to stimulate specific antibody. NECA As a very general rule, PSs with a molecular mass of 90,000 kDa are good immunogens in adults, while those with a molecular mass of 50,000 kDa are poorly immunogenic (8, 15, 20, 28). Coupling a PS or component oligosaccharide (OS) to a carrier protein to produce a conjugate molecule may result in immunogenic properties more like those of thymus-dependent antigens, including activation of higher levels of immunoglobulin G antibodies, enhanced memory responses, and immunogenicity in infants. The biochemical basis of immunogenicity to bacterial CPS has been extensively analyzed. Immunity following meningococcal infection is usually serogroup specific (33). Susceptibility to systemic disease is usually linked to an absence of detectable bactericidal antibodies (7). Antibody responses can be greatly affected by their physicochemical properties: e.g., molecular size, specific determinants, and conformation (19). Both the group Y meningococcal polysaccharide (GYMP) and group W-135 meningococcal polysaccharide (GWMP) are highly immunogenic and are currently used as components of a vaccine against meningococcal meningitis in humans (10, 16). In addition, a conjugate vaccine made up of these serogroups is now available (2). Antibacterial PS-specific antibodies are generally of low intrinsic affinity (9). Enhancement of antibody binding can be observed if the target antigen has a repetitive structure, making those polymers functionally multivalent (9). Evidence for length-dependent conformational epitopes experienced previously been reported for group B streptococcus type III (3, 31, 34), group B (13), type 14 (32), and type b (24) polysaccharides. It had been considered, in fact, that this acknowledgement of conformational epitopes may be a more general phenomenon than previously appreciated in the conversation of anti-PS antibodies with bacterial CPS antigens (32). It has been speculated that more stable conformational epitopes of PS species can result from the restriction of rotational movement of individual sugar residues and that these conformations may be favored by antibodies (24). In this study, we examined the nature of the group-specific epitopes present on GYMP and GWMP. Both of these PSs contain sialic acid. Conversation of sialic acid with the PS backbone experienced previously been shown to be important in defining the conformational epitope of group B polysaccharide III (3). (Portions of this work were presented at the 43rd Interscience Conference on Antimicrobial Brokers and Chemotherapy, Chicago, IL, 14 to 17 September 2003. ) MATERIALS AND METHODS Growth of group Y and W-135 meningococcal strains. Meningococcal Slaterus Y strain and meningococcal W-135 S4383 strain were provided by Carl Frasch (CBER/FDA, Bethesda, MD). The strains were grown in shake flasks under agitation at 37C in a altered Franz medium made up of glucose and yeast extract. Cultures were harvested by centrifugation at 8,000 rpm, and supernatants were Rabbit Polyclonal to PE2R4 collected and filtered through 0.22-m-pore filter models. The native Slaterus Y PS is usually 93%.