An application of PIXE method to cytolytic assay in immunological studies

Immunological studies have often been based on the results of cytolytic assay in which cells labelled with radioactive 51Cr are usually employed. The replacement of the radioactive isotope by a stable one is obviously desirable in order to eliminate the problem of radiation hazard and to prevent envirommental contamination. We applied PIXE (particle induced X-ray emission) method for the detection of stable chromium (Cr). MM46 cells labelled with natural Cr were treated with anti-MM46 serum and a rabbit complement. The remaining Cr was filtered. The released Cr was precipitated with ethanol and deposited on the filter. The specimens were bombarded with proton beams from a Van de Graaff accelerator and the X-rays produced were detected with a Si(Li) detector. The Cr peaks appeared clearly. One of the main advantages of the application of the PIXE method is its high sensitivity. Another merit of the present method is that it can easily compare the remaining ratio of several elements in cellular materials after lytic treatment. This information may be used as a parameter indicating differences in the process of cytolysis. (author)