CD4 and CD45 regulate qualitatively distinct patterns of calcium mobilization in individual CD4+ T cells

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Abstract
An early consequence of T cell activation is an increase in intracellular calcium concentration. Recent advances in video laser microscopic techniques enable the examination of individual cells over time following stimulation. Such studies have revealed that cells can undergo qualitatively distinct patterns of calcium mobilization, suggesting that different patterns of calcium flux may be associated with different signaling pathways and may differentially affect late events in cell activation. In this report, we identify distinct patterns of calcium mobilization in CD4+ T cells following the antibody‐mediated cross‐linking of either CD3 or CD4, or following the cross‐linking of both CD3 and CD4 simultaneously. These effects can be further modified by the cross‐linking of CD45. We find that antibody cross‐linking of CD3 alone induces a single spike in the vast majority of cells shortly after the addition of the cross‐linking antibody. In contrast, cross‐linking CD4 alone induces a delayed pattern of repetitive calcium spikes which are decreased in amplitude compared to CD3 cross‐linking. Simultaneous cross‐linking of CD3 and CD4 induces a sustained increase in intracellular calcium mobilization which is dependent on the presence of extracellular calcium. This sustained increase in intracellular calcium concentration is also seen following physiologic cross‐linking of CD3 and CD4 after T cell interaction with specific antigen and antigen‐presenting cells. Finally, the simultaneous cross‐linking of CD45, CD3 and CD4 abrogates the sustained increase in calcium seen following CD3 and CD4 cross‐linking. These results suggest that the qualitative nature of T cell receptor signaling can be modulated by the molecular association of other signaling molecules, which may be part of the T cell receptor complex or not.