from Case Western University
research group's attempts to better to characterize the activated, short-lived T cells that are typically present in the setting of untreated HIV infection.
used the radioactive label BrdU to identify S phase T cells in samples from HIV-infected individuals.He
found that a greater proportion of CD4 T cells were in S phase than CD8 T cells, which may be an interesting finding given that when other markers of T cell activation are used more CD8 T cells appear to be activated than CD4 T cells.The frequency of S phase T cells correlated with viral load levels.Both the CD4 and CD8 T cells in S phase displayed similar external markers: the activation molecule CD38 (but not two other potential markers of activation, CD25 and CD69), CD62L and CCR7 (two molecules associated with trafficking to the lymph nodes and generally found on resting, not activated, T cells) and CD45RO (a marker commonly used to identify memory T cells).
The S phase T cells also expressed high levels of caspase 3 (an enzyme associated with apoptosis) and low levels of bcl2 (a molecule associated with T cell survival), suggesting that these cells are indeed short-lived.Preliminary efforts to evaluate the specificity of the S phase T cells (i.e., which antigens they respond to) are underway.According to Sieg
, results so far indicate to be targeting antigens from HIV
although these analyses may be complicated by the tendency of recently activated T cells to temporarily down regulate the receptor they use for recognizing antigens (the T cell receptor or TCR).Sieg
stressed that this work is ongoing and more detailed results will eventually be presented and published.