Significance of non-pathogenic cross reactive bowel flora in patients with ankylosing spondylitis.

We have previously shown that antisera raised in rabbits to certain enteric cross reactive strains of bacteria are capable of specifically lysing the peripheral blood lymphocytes of HLA-B27 positive patients with ankylosing spondylitis (B27+ AS+). We now report that bacteria with cross reactive antigenic determinants are found in the bowel flora of all of 52 B27+ AS+ patients but in only one of 50 HLA-B27 positive normal controls (B27+ AS-). These organisms are functionally similar to the cross reactive enteric bacteria originally reported. They are not confined to a particular genus or species and their cross reactive serological nature appears to be a property shared by all enteric organisms isolated from B27+ AS+ patients. Organisms with these properties have been shown to persist in the bowel flora of 14 B27+ AS+ patients followed up for more than one year.