Antigenic diversity in the periodontopathogen, Actinobacillus actinomycetemcomitans

We have identified a significant level of variation in antibody responses to Actinobacillus actinomycetemcomitans outer membrane antigens (OMA). This study was designed to verify A. actinomycetemcomitans antigenic diversity that could contribute to maintaining this chronic infection despite the host immune response. A. actinomycetemcomitans strains (5 from different patients and 3 the same patient) were cultured and OMA prepared for Western immunoblotting studies. Antigen bands in the OMA were identified using 7 sera obtained from 3 adult periodontitis (AP) and 4 localized juvenile periodontitis (LJP) patients that were documented with elevated A. actinomycetemcomitans antibody and infection. Differences/similarities in the antigen patterns among the A. actinomycetemcomitans strains were assessed using a kappa similarity coefficient. Antigen bands in the A. actinomycetemcomitans strains ranged from 11-150 kDa; however, variation in antigen patterns were noted among the strains. Utilizing the human sera as probes for antigenic diversity, the 5 heterologous strains showed average K=0.23 (p < 0.05), while homologous A. actinomycetemcomitans strains had a K=0.48 (p < 0.02). The A. actinomycetemcomitans OMA were used as probes to describe variability in host antibody and as such presumptive evidence of antigenic diversity in A. actinomycetemcomitans that is colonizing each of the patients. The results showed average K=0.26 (p < 0.05) for the patients when tested against each of the heterologous strains, and K=0.14 when tested against the homologous strains (p > 0.1). Finally, antigen bands of M r 80, 65, 58, 31 and 20 kDa were demonstrated as antigens contributing to the antigenic diversity in A. actinomycetemcomitans.