Induction of high‐affinity paf receptor expression during T cell activation

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Abstract
Activated human T cells via the CD2 or the CD3 pathways exhibited a higher capacitythan resting T lymphocytes to incorporate and metabolize [3H] pafacether (paf) at 37°C. Resting T lymphocytes lacked specific binding capacity for paf, yet high‐affinity paf receptors (paf‐R) were inducedon CD3‐ or CD2‐dependent activation. This up‐regulation in the number of paf‐R became apparent by day 1 of culture, reached a maximum of about 25000 sites cell by days 4 to 6 and subsequently declined. Interestingly, human recombinant interleukin‐2 in a dose‐dependent manner prevented the decrease of high‐affinity paf‐R expression on T cells. By contrast, the receptor affinitywas constant throughout the culture period. Thus, paf‐R at different stages of Tcell activation were indistinguishable with respect to receptor‐ligand interaction, and differed only in their number. Together, these data demonstrate that after activation human T cells develop membrane high‐affinity paf‐binding sites. They also suggest for the first time that expression of the paf‐R are coupled to T cell activation and/or differentiation.