BTK protein but not mRNA expression is highly variable among CLL patients. (A) CD19⁺ cells from CLL patients (N = 30) were examined for BTK expression by immunoblot. Results are shown from 3 of 6 experiments. (B) RNA was extracted and converted to cDNA from CD19⁺ cells from CLL patients (N = 18) and CD19⁺ normal B cells (N = 5). RT-PCR analysis was done to determine quantities of BTK mRNA. Ct values are relative to 18S. Higher relative Ct values represent lower gene expression.