A caveat for clinicians- while what Mario says concerning levels of CD56+ T cells is true in most healthy Caucasian Americans, it is not necessarily true in Asians or other select populations and is not applicable in general to patient populations. Many disease processes, neoplastic and infectious, affect the levels of CD56+ T cells. Maryalice >>- 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 Maryalice Stetler-Stevenson Director Flow Cytometry Unit Laboratory of Pathology, NCI, NIH
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