Purpose of review: Spondyloarthritis (SpA) is a chronic immune-mediated inflammatory disease of unknown origin. Here we aim to review whether SpA is driven by T-cell and/or B-cell autoreactivity or by abnormal innate immune responses.
Recent findings: SpA does not share genetic risk factors, female predominance, presence of disease-specific autoantibodies and response to T-cell or B-cell-targeted therapies with prototypical autoimmune diseases like rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Growing evidence indicates that increased responsiveness of innate immune cells such as macrophages, mast cells and neutrophils drives inflammation in SpA. The altered innate immune response may be related to nonantigen-presenting functions of HLA-B27, including the induction of an unfolded protein response, and can be triggered by bacterial and mechanical stress. Innate immune cells appear to be the main producers of both pro-inflammatory (tumor necrosis factor, IL-1, IL-23, IL-17) and anti-inflammatory (IL-10) cytokines in SpA.
Summary: The predominance of myeloid above lymphoid alterations suggests an autoinflammatory rather than autoimmune origin of inflammation in SpA. Therefore, targeting innate cells or their inflammatory mediators may be more effective than T-cell or B-cell-directed therapies.