Streptococcal antigen in the pathogenesis of Behçet's disease

Patients with Behçet's disease (BD) are highly associated with HLA-B51 immunogenetically and tend to be involved with chronic infectious foci, such as tonsillitis and dental caries, by nonpathogenic streptococci in the oral cavity. BD patients were suggested to be hypersensitive to streptococci and we immunohistologically demonstrated the deposits of streptococcal related antigen at infiltrated cells which were adhering to the vascular walls in erythema nodosum (EN)-like lesions. The Japanese Research Group for BD also demonstrated that BD patients showed greater hypersensitivity against streptococcal antigens than normal healthy controls and that the BD symptoms were frequently induced by the skin tests using these antigens and the treatment of the dental caries. Streptococcus sanguis was dominantly isolated from the infectious foci and the strain strongly adhered to the epithelial cells of the oral membrane, which might be correlated with chemotactic activity of neutrophils in the BD lesions. An attempt at cloning and sequencing the bes-1 gene of S. sanguis isolated from BD patients was made and it has been found that the amino acid sequence of the bes-1 gene has more than 60% of homology with the human intraocular peptide brn-3b, which is a POU domain expressed in the retinal ganglion cells. On the other hand, heat shock protein-65 kDa (HSP-65) derived from microbial organisms which had homology with human HSP-60 was shown to be cross-reactive to the serotype of S. sanguis found in BD patients. Recently we recognized the antibody cross-reactivity against human HSP-60 peptide (336–351), which might stimulate T-lymphocytes of BD patients. In order to explain more precisely the relationship between S. sanguis and BD symptoms, we attempted to find bes-1 gene in the various lesions and to detect the antibodies against both bes-1 synthetic peptides and recombinant HSP-60/65 of S. sanguis in sera of BD patients.

Methodology

We performed PCR and PCR in situ hybridization (PCR-ISH) on the samples of BD lesions obtained by punch biopsy and controls using nested primers, which amplify the S. sanguis genomic region coding for bes-1, including the brn-3b homologous site. We also evaluated the antibody responses against bes-1 peptides and recombinant HSP-60/65.

Results

We detected the presence of bes-1 DNA in the samples of EN-like eruptions, and oral and genital aphthous lesions by PCR analysis. PCR-ISH also revealed bes-1 DNA gene located in the nuclei of the cells adhering to the vessel walls and macrophages infiltrated in EN-like lesions, whereas the antibodies against both bes-1 peptides and recombinant HSP-60/65 protein have not been detected in sera of these patients.

Conclusions

The presence of bes-1 DNA in macrophages infiltrated in the various lesions of BD patients suggests that the infectious foci by S. sanguis in the oral cavity are deeply correlated with the various lesions in BD patients. It is speculated that the clinical symptoms appear by the internalization of bes-1 DNA to macrophages infiltrated, as an extrinsic factor, in BD patients who are associated with HLA-B51-related gene as an intrinsic factor. However, it is not clear how S. sanguis infection is correlated with HLA-B51-related gene as the genetic background in BD patients.