Immune mechanisms: innate immunity

Innate immune mechanisms are strongly implied in the pathophysiology of spondyloarthritis (SpA). This chapter discusses available data on the role of the innate immune system in relation to HLA-B27, genetic associations, and the cellular and molecular characteristics of disease target tissue. Regarding the linkage with MCH-class I molecule HLA-B27, the chapter discusses the arthritogenic peptide hypothesis and three popular antigen-independent theories. The genetic architecture of the disease argues against a role for the adaptive immune system and identifies cytokine pathways, such as IL-1, TNF, and IL-23/IL-17. In experimental as well as in human SpA, the importance of these cytokine pathways are confirmed by effective reduction of signs and symptoms upon blockade of specific molecules. In-depth cellular and molecular analysis of the target tissue identifies a contribution of cells with strong innate features, rather than cells of the adaptive immune system.