FCN1 and arthritic joint disease: Reference mapping (Hao et al., 2024; Lotfollahi et al., 2024) showed that the majority of ICI-arthritis myeloid cells mapped onto four RA myeloid clusters: IL1B + FCN1 + HBEGF+, STAT1+ CXCL10+, SPP1+, and MERTK+ HBEGF+ clusters (Figure 3B).