Fig. 10. Correlation analysis shows 
-adaptin is more closely associated with endosomes containing IgA than with those containing Tf. Correlation coefficients were calculated comparing the 3-D distributions of -adaptin and either Tf or IgA (see Materials and Methods). Briefly, cells were labeled to steady state with either Tf or IgA, and then processed for -adaptin immunofluorescence. 3-D image volumes were collected, and 15 cells from each condition selected for correlation analysis. (A) Correlation coefficients, calculated for individual cells, are plotted against the total fluorescence of internalized Tf (closed circles) or IgA (open circles). Although variable, the correlations between IgA and -adaptin were uniformly higher than those between Tf and -adaptin, and largely independent of the levels of Tf or IgA fluorescence. (B) Bar graphs of the pooled data show a mean correlation coefficient of 0.29±0.05 between IgA and -adaptin, and a mean correlation coefficient of 0.14±0.04 between Tf and -adaptin. The potential range of this assay is demonstrated in cells labeled with a combination of Alexa488-Tf and Alexa568-Tf, which codistribute in the same compartments. Analysis of 15 cells yielded a mean correlation of 0.75±0.04. The mean correlation coefficient dropped to 0.01±0.07 when the region of analysis of one image of each pair was rotated 180°.
