OPTIMIZED FIXATION AND STORAGE-CONDITIONS FOR FISH ANALYSIS OF SINGLE-CELL SUSPENSIONS

In our protocol to isolate and identify fetal cells in maternal periph eral blood, antibody (Ab)-stained cells are preserved with paraformald ehyde (PF) before batch flow cytometric sorting. However, PF fixation compromises the quality of subsequent interphase fluorescence in situ hybridization (FISH). We therefore examined the effect of PF concentra tions and storage time in phosphate-buffered saline (PBS) on the quali ty of FISH signals. Cells were analyzed for changes in light scatter, morphology, and accessibility of target cell DNA. Fixation in 3% PF fo r 1 hr was ideal for both flow cytometry and subsequent FISH detection . However, beyond 10 days of storage, FISH duality deteriorated.