Real-time uptake of Cy5-conjugated anti-Ri immunoglobulin G in living cultures compared with uptake in parallel cultures following fixation at the same time points. In cultures studied in real time, Cy5 conjugated anti-Ri immunoglobulin (Ig)G was visible within multiple neuronal populations at 6 hours, with an increase in intensity of intraneuronal IgG by 24 hours, similar to observations with anti-Hu IgG. Uptake of Cy5-conjugated anti-Ri IgG in parallel cultures fixed following incubation with antibody were indistinguishable from that observed in slice cultures studied in real time, confirming that IgG uptake seen in fixed cultures accurately reflected events occurring prior to fixation. Neurons containing Cy5-conjugated anti-Ri IgG at both time points excluded SYTOX dyes, indicating that antibody uptake had occurred in living cells. Images are representative of real-time studies employing anti-Ri sera from two different patients, carried out in triplicate. Magnification bar indicates 20 μm.