The mononuclear cells of the inflamed synovial membrane.
D000818:Animals; D001172:Arthritis, Rheumatoid / Q000473:pathology*; D006168:Guinea Pigs; D006801:Humans; D008214:Lymphocytes / Q000473:pathology*; D010950:Plasma Cells / Q000473:pathology*; D013583:Synovial Membrane / Q000473:pathology*