Cosedimentation of ICs and MPs. (A) Fluorescent microscopy images of antihuman IgG-FITC or antihuman IgM-FITC-stained 20 500g pellets from RA and OA SFs. Images were captured at room temperature using a Zeiss LSM 510 Meta confocal laser scanning microscope equipped with an inverted Axiovert 200M microscope, 63× Plan Apochromat oil immersion differential interference contrast objectives (numerical aperture, 1.4). The acquisition software was AIM LSM, Version 4.2. (B) The 20 500g pellet from RA SF was analyzed by immune EM, stained with antihuman IgG-HRP or antihuman IgM-HRP. Arrowheads indicate immunopositive structures among MPs. Original magnification × 50 000. Scale bar represents 400 nm. Images were captured at room temperature using Hitachi 7100 electron microscope equipped with a Megaview II digital camera. (C) FC analysis revealed that isolated ICs were present in the pellet and were nearly absent in the supernatant (SN). (D) Isolated IgG or IgM ICs from RA SFs were also analyzed by DLS. The x-axis is set to logarithmic scale; a(r_h) denotes the coefficient of autocorrelation function of the scattered electric field. DLS experiments were carried out at 21°C.