Sorted cells were used for RNA isolation and RT-PCR following an overnight recovery. CCSP mRNA expression was detected in CCSP + cell fraction, but not in CCSP 2 cells ( Figure 3A) . We also mounted cells on slides using Cell Adherence Media for immunofluorescence (IF). We found that 98% (225/ 230) of the cells in CCSP + sorted fraction were positive for CCSP IF. We also found that 97% of the cells in the CCSP + fraction revealed the expression of another Clara cell maker UGRP1 by IF. All of the cells in CCSP + sorted fraction expressed pan-keratin. Rare CCSP + sorted cells revealed the presence of pro-SPC ( Figure 3) . These data demonstrated that sorting by flow cytometry is a useful and simple method for harvesting purified CCSPcontaining Clara cells. 