Flow cytometric analysis of cellular BTK expression in a normal donor and in an XLA patient (family 19) and his mother. Dot plot maps of BTK versus CD20 gated for lymphocytes (A) and histograms gated for CD14⁺ monocytes (B) were obtained as described in the legend of Fig 2. Five thousand cells were evaluated in each gated population. The dashed line indicates the control antibody.