A factor in the culture filtrate of some Klebsiella isolates specifically modifies the fibroblasts of HLA-B27-positive normal individuals.

Cultured skin fibroblasts of HLA-B27-positive clinically normal individuals specifically bind, and are modified by, a factor in the culture filtrate of some Klebsiella isolates. These modified fibroblasts are serologically similar to the cells (lymphocytes and fibroblasts) of B27-positive patients with ankylosing spondylitis (B27+AS+). By contrast, B27+AS+ cells fail to bind the factor, presumably because a receptor present on B27+AS- cells has already been blocked or modified by a Klebsiella antigen in vivo.