This 1983 study describes the isolation and characterization of protein P1, a high molecular weight extracellular protein from Streptococcus mutans strain Ingbritt grown in chemostat culture. The researchers purified P1 to homogeneity using ammonium sulfate precipitation and column chromatography, confirming it was free of glucosyltransferase and other antigens. Physico-chemical analysis revealed P1 has a molecular weight of 185,000 Da and an isoelectric point of 5.40, properties identical to previously identified antigens B and 1/11 from other laboratories, suggesting these are the same protein. Serological studies confirmed this identity. Importantly, antisera against P1 bound to rabbit heart tissue and other organs, demonstrating mammalian tissue cross-reactivity. Rabbits injected with purified P1 showed significantly increased mononuclear leucocyte infiltration in heart tissue compared to controls, though whole bacterial cells did not produce this effect. These findings raise safety concerns about using P1 as a caries vaccine, despite its potential efficacy, and suggest alternative antigens like antigen A warrant further investigation for vaccine development.

Key findings

• Protein P1 is identical to previously identified antigens B and 1/11 based on physico-chemical and serological properties, with molecular weight 185,000 Da and isoelectric point 5.40
• P1 antiserum shows significant cross-reactivity with multiple mammalian tissues, particularly heart ventricular muscle, suggesting molecular mimicry between bacterial and host antigens
• Injection of purified P1 into rabbits induced statistically significant mononuclear leucocyte infiltration in heart tissue, indicating a potential autoimmune response
• P1 was successfully purified free of glucosyltransferase and other contaminating proteins using optimized culture conditions and multi-stage chromatography
• The tissue cross-reactivity and inflammatory response to P1 raise safety concerns for its use as a dental caries vaccine despite potential efficacy