Immunolocalisation of mast cell tryptase, tumour necrosis factor(TNF)-α, interleukin (IL)-1α and IL-15 in the rheumatoid lesion.(a) Micrograph showing mast cell tryptase (red) with extracellularstaining indicative of mast cell (MC) activation associated with localizedoedema (arrow) and TNF-α expression (brown) by a proportion of mononuclearcells. (b) Micrograph showing mast cell tryptase (red), local MCactivation and associated mononuclear cells stained for IL-1α (brown).(c) Low power micrograph showing distribution of mast cells (tryptase,red) and their degranulation in rheumatoid synovial tissue. (d) Consecutive section to (c) stained for IL-15. Note the absence of IL-15from MC activation sites. (e) Micrograph of cartilage-pannus junction showingboth extracellular and intracellular staining for IL-15 (red). Note themicrofocal nature of cytokine production by a minority of cells. (f) Micrograph of rheumatoid lesion showing chondrocytic cells stained forIL-15 (red) with little evidence of cytokine production by the overlying pannustissue (to right of micrograph). Bars: (a) and (b) 35 μm;(c) and (d) 120 μm; (e) 35 μm; and (f) 45 μm.