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Pfizer Global Research and Development, Fresnes, France
To study the requirements for activation of human Th1 and Th2
cells, soluble peptide/DR1 complexes were prepared from naturally
expressed DR1 protein. When immobilized, this material induced T cell
activation, as revealed by CD25 up-regulation. Unexpectedly, Th2 cells
required a higher density of peptide/DR1 complexes than Th1 cells to
initiate CD25 up-regulation. Similar findings were obtained with
immobilized or soluble and cross-linked anti-CD3 mAb. In contrast,
peptide/DR1 complexes displayed on the surface of nonprofessional APC
similarly induced CD25 up-regulation in Th1 and Th2 cells. Signaling
events distinguishing human Th1 and Th2 cells following TCR engagement
by anti-CD3 mAb were then studied. It was observed that upon TCR
triggering, the overall tyrosine phosphorylation profiles were fainter
in Th2 than in Th1 clones. Similar results were obtained with Th1- and
Th2-polarized polyclonal lines. Varying the dose of anti-CD3 mAb,
the kinetics of activation, and coengagement of CD3 and CD28 failed to
increase tyrosine phosphorylation in Th2 cells to levels reached in Th1
cells. In contrast, treatment with the tyrosine phosphatase inhibitor
phenylarsine oxide resulted in similar tyrosine phosphorylation levels
in Th2 and Th1 cells. These findings indicated that Th2 cells had an
intrinsically lower TCR-induced tyrosine phosphorylation capacity than
Th1 cells, which might be controlled by Th1- and Th2-specific
phosphatase profiles. Finally, a weaker association was found between
ZAP-70 and CD3
in Th2 than in Th1 cells after TCR engagement. Taken
together, these results constituted evidence that early events in the
TCR signaling cascades are distinct in human Th1 and Th2
cells.
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