Fig. 1.

Intestinal and gut barrier involvement in early SpA

These bacterial molecules are known as PAMPs and may directly enter the circulation and potentially trigger inflammation at sites of high mechanical stress. Secondly, the impact of DAMPs may activate local innate immune cells to produce pro-inflammatory cytokines and other molecules that may enter the circulation. Thirdly, the possibility remains that the activated innate immune cells may circulate to entheses and bones as part of a gut–enthesis axis. PRR: pattern recognition receptors; PAMPs: pathogen-associated molecular patterns; NLR: nucleotide-binding oligomerization domain (NOD)-like receptors; TLR: Toll like receptors; RIG-I-like: retinoic acid-inducible gene-I-like receptors.