CD38 is laterally associated with CD16 on the membrane of YT CD16⁺ cells.

(A) Cells were stained with Cy3-conjugated CD38 mAb and the indicated FITC-conjugated mAb. FITC was excited at 488 nm and Cy3 emissions were collected at more than 600 nm. The cytofluorographic profiles show representative data from 3 independent experiments. Each quadrant shows Cy3 emissions at more than 600 nm in the absence and presence of the indicated FITC-conjugated mAb. A right shift of the curve indicates FRET. (B) Bar graph shows the mean ± SD for the median fluorescence intensities on the membrane of YT CD16⁺ cells, expressed as median fluorescent channels derived from the results of 3 independent experiments. The asterisk indicates the CD16 FRET that is significantly higher than the CD71 FRET in the same cell line (P < .05; Wilcoxon matched pair, signed rank test). (C) Capping of the CD38 molecules induces cocapping of CD16 but not of HLA class I molecules. The same result was obtained by reverting the order of the mAbs, ie, by capping with CD16 and cocapping with CD38. The table shows cumulative data from several experiments. The numbers of caps and cocaps is presented as a percentage of cells analyzed. Cells showing partial redistribution of the surface molecule detected by the primary capping antibody were excluded from the analysis. The asterisks indicate a significant difference. Original magnification × 50.