>- In the CD56+ population I also observe 2 intensities: does anyone know >what these two populations represent? Is it possible that the CD56high >cells are gamma-delta cells? No, these are not gamma-delta T cells. They are both NK populations; the "bright" CD56+ population is thought to be an early differentiation stage of NK. The cells are uniformly CD94+ and do not express other "kir" molecules. (That's not to say that there aren't CD56+ T cells--but these are pretty rare and are swamped by the large excess of NK cells in PBMC. If you gate on CD3+, then you will see the CD56+ T cells.) >- I see a CD4low population (monocytes) and a reminescent CD4high, but I >see the same phenomenon with CD8 (sometimes there's a nice segregation >between the two, but in most cases there isn't): are the CD8low cells NK >cells? Some CD8-low cells are NK cells; others are "IEL-like" (intra-epithelial lymphocyte) T cells that are probably extra-thymic in origin. These cells actually express just as much CD8-alpha as "regular" T cells, but the CD8 is comprised of only CD8a/a homodimers rather than CD8a/b heterodimers. The reason they appear less bright in CD8 is that the typical CD8 antibody we use has a much higher affinity for CD8a/b and is titred with that in mind--so the CD8a/a molecules are not saturated (hence less bright). If you put in 10x more CD8 antibody, you will find that the "CD8-dull" cells are actually just as bright as the "CD8-bright" cells. mr
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