Representative kinetic traces illustrating the JRA-associated abnormality in metabolic oscillations of neutrophils. These traces show NAD(P)H autofluorescence intensity (ordinate) versus time (abscissa); to conserve space, only a few oscillations are shown. Polarised cells were studied on glass slides at 37°C. Using an anti-MPO antibody in immunofluorescence microscopy, JRA neutrophils can be classified as MPO-negative (left) and MPO-positive (right). Untreated MPO-negative cells demonstrated NAD(P)H oscillations with a period of approximately 20 seconds (trace a). The NAD(P)H oscillatory period of these cells decreased to 10 seconds in the presence of the activator LPS. In patients with JRA, a subpopulation of neutrophils are MPO-positive. In the absence of cell stimulation, MPO-positive cells cannot be distinguished from MPO-negative cells. However, in contrast to MPO-negative cells, MPO-positive cells undergo both a decrease in period to 10 seconds and a dramatic increase in the oscillatory amplitude. JDA, juvenile rheumatoid arthritis; LPS, lipopolysaccharide; MPO, myeloperoxidase; NAD(P)H, nicotinamide adenine dinucleotide (phosphate).