PDCD1 and ankylosing spondylitis: We did not apply limits for the year of publication and used the following terms “spondyloarthritis” and “ankylosing spondylitis” in combination with “CD28, CD80, CD86, ICOS, ICOS-L, CD40L, CD40, OX40, OX40L, 4-1BB, 4-1BBL, CD27, PD-1, PD-L1, PD-L2, CTLA-4, TIM-3, B7-H3, B7-H4, FGL1, ICOS-L, CD160, BTLA, HVEM, TNFRSF14, CD70, B7-H7, B7-DC, GITR-L, GITR, OX40L, 4-1BBL, TIMG02, B7-DC, Galactin9, LIGHT”.