Etiology of a spontaneous autoimmune joint disease in mice

Aims

To reveal which microbes are capable of inducing Ankylosing Enthesopathy (ANKENT), a spontaneous joint disease in susceptible mouse strains. Besides gender and age (young males afflicted) and genes (B57B6 background with some H-2 haplotypes being more effective), environmental factors (stress and microflora) have also been suggested to play a role in ANKENT onset. We have recently shown that ANKENT does not develop under germfree (GF) conditions.

Materials and methods

To identify ANKENT-triggering bacteria we transferred B10.BRANKENT-prone mice into germfree conditions. Individual colonies were then associated with selected microbial cocktails. The incidence of ANKENT and immune system development has been studied in these gnotobiotic colonies.

Results

When compared to GF and conventional (CV) males (prevalence of 0 and ~20%, respectively), high incidence (~20%) of ANKENT has been revealed in mice associated with a cocktail of bacteria isolated from the intestine of an ANKENT-afflicted CV male. In the cocktail, no strong pathogens and Enterobacteriae like E.coli or Salmonella were present. The first ANKENT case has also been observed in mice colonized with a more restricted cocktail containing two selected gram-positive microbial strains. Surface phenotype of lymphocytes isolated from systemic lymphatic tissues, MALT and diseased joint were characterized. No significant differences in lymphatic tissues were detected between individual experimental groups. However, the prevalence of CD4⁺ cells among joint-infiltrating lymphocytes was recorded.

Discussion

The presence of viruses, eukaryotic micro-organisms and noncultivable bacterial species (like segmented filamentous bacteria) is not required for ANKENT incidence. Although the autoimmune nature of the disease has not definitely been proven yet, the existence of specific ANKENT-triggering microbes strongly supports this hypothesis. The ANKENT-triggering agents are currently characterized by rRNA analysis.