Identification of mononuclear cells in human blood. I. Qualitative and quantitative data on surface markers after formaldehyde fixation of the cells.

The technical details of a fixation procedure with formaldehyde which was applied in a direct membrane immunofluorescence technique to mononuclear cells from normal human blood are described. After separation of the cells with Ficoll--Isopaque according to Böyum (1963) they were washed and fixed with 0 . 04% formaldehyde in PBS for 10 min and washed again. This cell suspension can be stored at 4 degrees C for at least 24 hr and the slides prepared from them at -20 degrees C for at least some months. In practice, this fixation procedure not only appeared to be effective in the preservation of cells but also showed a number of additional advantages, such as the short handling period, including the fixation procedure and the avoidance of loss of cells. Moreover, true B lymphocytes, as defined by the synthesis of immunoglobulins and the incorporation of these molecules into their cell membrane, are recognized convincingly.