Mark, there has been a number of discussions on this list regarding
RA/RO... I'm not going to rehash those discussions, since I don't
want to bore everyone else. Go to the archives and read over the
material -- it includes references.
But once again, CD45RA+ cells are BOTH naive AND memory. You CANNOT
use RA and/or RO to identify naive T cells without an additional
marker such as CD62L, CD11a, CD27.
As for "Double-positive", it depends on how you define "positive".
Bright ("true") RA+RO+ double positives are very rare in peripheral
blood but common in active tissues (like tonsil). Cells positive for
one and dull for the other are normal resting memory T cells. There
are no double-negative cells that are viable.
Percentages in the peripheral blood are meaningless for the simple
reason that RA+ cells are a heterogeneous mixture of naive & memory.
Especially the CD8's, where anywhere between 20 and 80% of RA+ cells
can be memory. (In CD4, most (95%) are naive; however, in many
disease states including HIV, this fraction drops to under 50%).
mr
>Hello Flowers,
>
>I'm looking at CD45RA and RO expression on CD4 and CD8 T cells. Could
>somebody confirm for me whether these markers are mutually exclusive
>regarding their expression upon the cell membrane? I know that the naive
>cells are CD45RA+ and the CD45RO+ cells are memory cells, but is it possible
>to have double positive CD45RA+CD45RO+ T cells, or double negative
>CD45RA-CD45RO- T cells?
>If so, what percentages would be expected in the peripheral blood?
>
>
>I would love to have a reply from somebody in the know!
>
>Thanks,
>Mark
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