CD19 and B-cell chronic lymphocytic leukemia: In CLL patients, the frequencies of both Tfh and Tfr cells positively correlated with peripheral CD19+ B cell numbers (Tfh %, r = 0.336, p = 0.039; Tfr %, r = 0.379, p = 0.019; Tfh absolute, r = 0.307, p = 0.061 [trend]; Tfr absolute, r = 0.449, p = 0.005), while no such associations were observed in HCs.