Unfortunately there is little consensus on how to quantitate antigen expression. Calibrations beads to convert relative fluorescence intensity (preferably median, rather than mean) are one approach, such as MESF units. In clinical practice I have evolved to a rather simple approach of reporting antigen "density" in terms of + (less than normal cell counterpart), ++ (similar to normal cell counterpart), and +++ (higher than normal cell counterpart). For example, CLL is typically CD20+, being less CD20 expression than seen on normal B cells, which would be defined as CD20++. This approach does not require additional expense in beads and software and allows for "corrections" between instrument types and PMT settings, as well as F/P ratio differences between antibody clones. However, I am the first to admit this is far from universally accepted or used, but does circumvent the problems with the arbitrary practice of quantify by the position on a log scale. Another approach is to ratio the fluorescence intensity to a reference bead or known cell population (Janis Giorgi advocated using CD4 T cells). This lack of consensus in quantitative cytometry is increasingly becoming problematic, but is beginning to be addressed by the European working group and efforts have also started by the Clinical Cytometry Society to drive a scientifically based consensus definition. So stay tuned....... Regards, Bruce H. Davis, M.D. Maine Medical Center Research Institute 81 Research Drive Scarborough, Maine 04074 USA PHONE: 207-885-8113 FAX: 207-885-8110 Email: davisb@mmc.org >>> "LEE Wing-Keung" <wklee@ha.org.hk> 10/11/01 01:09PM >>> Dear Flow-ers, Could you kindly give some opinions on the following question? 1. What are the significants of quantitative analysis of antigen expression (e.g. for those cases of immunophenotyping of malignant haematological diseases? 2. How / What are the criteria to define the dim, intermediate or strong antigenic expression? For example: dim for those overlapping the isotopic cutoff, intermediate for those behind the isotopic cutoff and strong for those with 2 log scale of the isotopic control. As coded in Haematologic 2001; 86:675-692, they suggested to use median fluorescence intensity (MFI). Any idea? Best Regards, W.K. LEE United Christian Hospital, Hong Kong, China.
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