Double immunofluorescence of human neutrophil peptides 1-3 (HNP1-3) and human β-defensin 2 (HBD 2) in synovial tissue of an RA patient. Arrowheads show double-positive cells. Left panels: HNP1-3 (red staining) were co-localized with neutrophil elastase (green staining), as indicated by the yellow color in this overlay image. Right panels: HBD-2 (red fluorescence) was rarely detected. Some fibroblasts (green fluorescence in the upper right panel) and some CD19+ B lymphocytes (green fluorescence in the lower right panel) stained positive for HBD-2 (yellow overlay). Magnification 400×.