Antigenic variation in Porphyromonas gingivalis ribotypes recognized by serum immunoglobulin G of adult periodontitis patients

We obtained clinical isolates of Porphyromonas gingivalis of known ribotype from patients diagnosed with adult periodontitis and used Western blot met hodology to evaluate profiles of antigens recognized by IgG in heterologous and homologous patient sera. Our aims mere to identify isolates belonging to different serogroups, to learn if serogroup membership is related to rib otype, to assess variation in IgG responses of patients to antigens in homo logous and heterologous ribotypes, and to determine the frequency of shared and variable antigens in different biochemical classes recognized across d ifferent serogroups and ribotypes. Blots of separation patterns of 28 isola tes were developed in sera from patients and bound IgG was quantified by di gital image densitometry. The membership of isolates in different serogroup s was determined by correlation and hierarchical cluster analysis of isolat e whole-cell IgG binding profiles. Two major isolate clusters, each with tw o subclusters, were found, Isolates within the same ribotype clustered toge ther in some cases but not others. Homologous isolates ranked high in IgG b inding levels relative to those from different patients irrespective of rib otype. Patient subgroups with Ige responses dominant for different ribotype s and serogroups were revealed by correlation analysis. The IgG binding pro files observed for individual protein and proteinase-resistant antigens acr oss both homologous and heterologous isolates were very dissimilar. Further more, the frequency of antigens both shared across all ribotypes and recogn ized by IgG in patient sera was unexpectedly low. Only two protein antigens (Mr 44 kDa and 27 kDa) a ere strongly recognized across all ribotypes by d ifferent sera. We conclude that the IgG response of patients infected with a particular P. gingivalis serotype or ribotype is directed mainly against antigens that are not shared by other potentially infective clonal types.