I couldn't agree more with your (Alice Givan's) recent comments on the importance of quantification of activation antigens. In "normals", there will be some variation in the number of circulating T-cells expressing any particular activation antigen at any particular level because so-called "healthy" people will have been exposed to different levels of subclinical immunologic challenge before the blood sample was taken. However, many if not most activation antigens are present at low levels on unstimulated cells, and, as one uses more sensitive instruments and more specific reagents, one will discern a higher fraction of "positive" cells. It makes more sense to follow and report the median and percentiles (25th and 75th, 5th and 95th, or both) of numbers of antigens on defined subpopulations (CD3+CD4+, CD3+CD8+, or even finer distinctions) than to express results in terms of "positive" and "negative"; the only problems are 1)that we have to reach consensus on quantification before we can start doing this, and 2)that we'll have to recognize that data taken up to this point are of limited use. -Howard
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