T cell activation: in vivo veritas.
Phenotypic changes in CD4(+) T cells undergoing antigen-dependent activation were compared in vivo and in vitro. The most obvious difference was in expression of CD25, the alpha chain of the high affinity receptor for IL-2. High level expression of CD25 in vivo is restricted to a small fraction of the cells at the leading edge of the cell division profile, whereas all activated cells express high levels of CD25 in cultures responding to antigen. Because IL-2 is known to upregulate expression of CD25 in preactivated T cells, this suggests a difference in IL-2 exposure in the two responses. A number of other markers, including CD54, show a similar difference in the pattern of expression in vivo and in vitro. Using 6-colour flow cytometry, it was demonstrated that the small percentage of cells expressing CD25 in vivo coexpresses a very high level of a number of other activation markers, including CD38, CD44 and Ly-6A/E, suggesting that these may also be upregulated by autocrine IL-2.
Fazekas de St  Groth
Barbara
B
Centenary Institute of Cancer Medicine and Cell Biology, Newtown, NSW 2042, Australia. B.Fazekas@centenary.usyd.edu.au
Smith
Adrian L
AL
Higgins
Caroline A
CA
D000818:Animals; D015703:Antigens, CD / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002455:Cell Division / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008822:Mice, Transgenic; D011948:Receptors, Antigen, T-Cell / Q000235:genetics / Q000276:immunology*; D015375:Receptors, Interleukin-2 / Q000276:immunology*
D015703:Antigens, CD; D011948:Receptors, Antigen, T-Cell; D015375:Receptors, Interleukin-2