Immunodominant antigens of Actinobacillus actinomycetemcomitans serotypes a and c in high‐responder patients

Abstract

This study was undertaken to examine the characteristics of the immunodominant antigens of Actinobacillus actinomycetemcomitans serotypes a and c. The top responders for A. actinomycetemcomitans serotypes a and c were selected (19 for serotype a and 21 for serotype c) from 150 clinically characterized patients. Competition assays revealed that 9 of 19 of these patients were reacting specifically to serotype a and 12 of 21 for serotype c. Limiting dilution analysis on Western blots revealed that most antigen bands apparent at low dilution disappeared as the patient's serum was diluted. The antigen band(s) remaining at the endpoint or the dilution corresponding to the antibody titer were defined as immunodominant. For serotype a there were several different immunodominant antigens but none was present in more than half of the subjects. For serotype c the immunodominant antigens included a number of discrete bands and a diffuse smeared polysaccharide band. Only 2 of these antigens were present in the majority of the high-responders: 92% had the smeared antigen and 67% had a 15 kDa antigen. The 15 kDa band was a protein common to all A. actinomycetemcomitans serotypes. The smeared antigen was unaffected by protease K treatment and gave a reaction of identity with the serotype c specific rabbit antiserum. This rabbit antiserum is specific for a mannan carbohydrate and does not react with LPS (23). Therefore, the smeared immunodominant antigen appears to be a polysaccharide containing mannan.

DestructivePeriodontitisLesions areDetermined by theNature of theLymphocyticResponse

“…However, different patterns of immunoreactivity with periodontopathic bacteria have been demonstrated for A. actinomycetemcomitans (Califano et al ., 1991(Califano et al ., , 1992Engström et al ., 1993;Ebersole et al ., 1995) and for P. gingivalis (Curtis et al ., 1991;Kurihara et al ., 1991;Polak et al ., 1995). Since these responses are regulated by immunoregulatory genes, it may be that antibody responses are protective in one individual but not in another (Offenbacher, 1996).…”

Actinobacillus actinomycetemcomitans Serotype b Lipopolysaccharide Mediates Coaggregation with Fusobacterium nucleatum

“…The chemical structures of the A. actinomycetemcomitans serotype a to f antigenic O-PSs were determined (7,17,18), and the DNA sequences of the genes involved in their synthesis have been described previously (7,14,15,25,28,29). The structural differences between these antigens are the basis for the absence of cross-reactivity among the different A. actinomycetemcomitans serotypes (1,22), with the exception of serotypes b and f, which show serological cross-reactivity, probably due to a common ␤-N-acetyl-galactosamine epitope (7).…”

“…Of these strains, serotype b is most frequently isolated from subjects with localized juvenile periodontitis (30,31), who exhibit elevated serum antibody levels to serotype b-specific antigen (1,22). The serotype b O-PS region of the LPS (18) consists of a polymer of repeating trisaccharide units with the structure…”

“…A. actinomycetemcomitans strains isolated from the human oral cavity are divided into six serotypes, a to f (3,7,19,31). The serotype-specific antigens are major targets of the humoral response in periodontitis patients colonized by these species (1,22). These antigens are located in the O-polysaccharide (O-PS) region of the lipopolysaccharide (LPS) (16,18,27).…”

Actinobacillus actinomycetemcomitans Serotype d-Specific Antigen Contains the O Antigen of Lipopolysaccharide

“…The composition and location of the antigen have been studied extensively (1,18,23,34). Researchers agree that the antigen is composed of polysaccharide, but whether it resides in the capsular polysaccharide distinct from lipopolysaccharide (LPS) (1,3) or in the polysaccharide moiety of LPS (18,34) is still unclear. Further attempts to characterize the serotype-specific antigens are needed to advance understanding of the role of A. actinomycetemcomitans as a human pathogen and to clarify why serotypes are distributed differently in geographically distant populations, in periodontal health and disease, or among various periodontal diseases.…”