Quantitative evaluation of gene expression in freshly isolated human respiratory epithelial cells

Recent advances in molecular biology have led to development of methods to evaluate the in vivo expression of specific genes in epithelial cells of the human respiratory tract. These methods involve collection of small samples of respiratory epithelium from the human airway with a cytology brush, together with sensitive techniques to enumerate cells and to detect and quantify RNA using the polymerase chain reaction (PCR). Thus, using the typical kinds of tissue samples obtainable in a clinical setting, one can now evaluate in vivo expression of specific genes in human airway epithelium. Specifically, mRNA transcript levels can be determined on a copy number per cell basis even when the level of expression is in the range of 1-10 mRNA transcripts/cell. The currently available techniques for measuring mRNA transcript levels in small tissue samples are reviewed with emphasis on the use of quantitative PCR assays.