Study of cell antigens and intracellular DNA by identification of element-containing labels and metallointercalators using inductively coupled plasma mass spectrometry.

The enumeration of absolute cell numbers and cell proliferation in clinical samples is important for diagnostic and research purposes. Detection of cellular DNA with fluorescent dyes is the most commonly used approach for cell enumeration in cytometry. Inductively coupled plasma mass spectrometry (ICPMS) has been recently introduced to the field of protein and cell surface antigen identification via ICPMS-linked immunoassays using element-labeled affinity reagents such as gold and lanthanide-conjugated antibodies. In the present work, we describe novel methods for using metallointercalators that irreversibly bind DNA and low concentrations of rare earth metals added to cell growth media for rapid and sensitive measurement of cell numbers by mass spectrometry. We show that Ir- and Rh-containing metallointercalators are useful reagents for labeling cells and normalizing signals when studying antigen expression on different types and numbers of cells. Results are presented for solution analysis performed by conventional ICPMS and compared to measurements obtained on the novel flow cytometer mass spectrometer (FC-MS) instrument, designed to analyze multiple antigens and DNA simultaneously in single cells.