ACTA1 and rheumatoid arthritis: To investigate the presence and distribution of the fibroblast-like myeloid cell populations across RA pathotypes, we deployed multicolor immunofluorescence in the synovium sections of patients to assess the expression of their markers, including CD45, CD68, α-SMA, COL3A1, and CD163 Sections of 9 patients (lymphoid: myeloid: fibroid = 3: 3: 3) were included.