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TCR Comodulation of Nonengaged TCR Takes Place by a Protein Kinase C and CD3 Di-Leucine-Based Motif-Dependent Mechanism ¹

Charlotte Menné Bonefeld^*, Anette B. Rasmussen^*, Jens Peter H. Lauritsen^*, Marina von Essen^*, Niels Ødum^*, Peter S. Andersen and Carsten Geisler^2,*

^* Institute of Medical Microbiology and Immunology, Panum Institute, University of Copenhagen, Copenhagen; and Symphogen, Lyngby, Denmark

One of the earliest events following TCR triggering is TCR down-regulation. However, the mechanisms behind TCR down-regulation are still not fully known. Some studies have suggested that only directly triggered TCR are internalized, whereas others studies have indicated that, in addition to triggered receptors, nonengaged TCR are also internalized (comodulated). In this study, we used transfected T cells expressing two different TCR to analyze whether comodulation took place. We show that TCR triggering by anti-TCR mAb and peptide-MHC complexes clearly induced internalization of nonengaged TCR. By using a panel of mAb against the Ti chain, we demonstrate that the comodulation kinetics depended on the affinity of the ligand. Thus, high-affinity mAb (K_D = 2.3 nM) induced a rapid but reversible comodulation, whereas low-affinity mAb (K_D = 6200 nM) induced a slower but more permanent type of comodulation. Like internalization of engaged TCR, comodulation was dependent on protein tyrosine kinase activity. Finally, we found that in contrast to internalization of engaged TCR, comodulation was highly dependent on protein kinase C activity and the CD3 di-leucine-based motif. Based on these observations, a physiological role of comodulation is proposed and the plausibility of the TCR serial triggering model is discussed.

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