Since pro-inflammatory cytokines and chemokines and inflammation-inducing transcription factors play key roles in the pathogenesis of MPA and GPA [14], TREM-1-related signalling could be inferred to reflect systemic inflammation; based on this theoretical background, several previous studies have demonstrated the clinical role of sTREM-1 in various autoimmune diseases including rheumatoid arthritis, systemic lupus erythematosus, and Behcet disease [[15], [16], [17]]. Here, TREM1 is linked to granulomatosis with polyangiitis.