CD81 and posterior cortical atrophy: Figure 2 also shows that the CA IX band corresponded to the typical exosome fractions as identified by the expression of Alix and CD81 in the second and third fractions of the density gradient. As shown in Figure 2(A), CA IX in PCa exosomes is evidenced by the presence of two bands (58/54 kDa). The CTR exosomes (Figure 2(B)) exclusively showed the Alix and CD81 bands.