(p. 63) Immune mechanisms: adaptive immunity 

The role of adaptive immunity (i.e. the involvement of B and T lymphocytes) in the pathogenesis of axial spondyloarthritis has been investigated in both human disease and relevant animal models. Studies of B cell responses have not generally implicated an autoantibody in the disease, but there are abnormalities of antibody responses, particularly increased titres of antibodies to various gut bacteria. T cells are critical to the disease in animal models other than those where overexpression of a cytokine is engineered, suggesting that they are the drivers of the inflammatory response. There is convergent evidence from animal models, genetics in humans, and direct observation of human peripheral blood and joints to implicate T cells producing IL-17 under the influence of IL-23. These in turn may be responding to bacteria either in the gut or on the skin.