Membrane trafficking of CD1c on activated T cells

We investigated the regulation of and the intracellular traffickinginvolved in the membrane expression of CD1c antigen on activated matureT cells. Membrane expression of this glycoprotein was highly regulatedand dependent on the activation state of the cells. The presence of the CD1c antigen on activated peripheral blood mononuclear cells (PBMCs)was confirmed by flow cytometry, reverse transcriptase‐PCR (RT‐PCR),and immunoperoxidase staining. The RT‐PCR analysis of the α3‐ and3′‐untranslated regions of CD1C showed thatphytohemagglutinin (PHA) activation induced expression of transcriptsthat encode the three isoforms (soluble, membrane, andcytoplasmic/soluble). Immunocytochemical studies showed a specificassociation of CD1c with the cell membrane and a cytoplasmic, perinuclear distribution. Although flow‐cytometric staining confirmedthe intracellular presence of CD1c, membrane expression on PHA blastcells was not detected. We found that membrane detection of CD1cantigen was temperature dependent. Cell surface binding of theanti‐CD1c monoclonal antibody (mAb) was consistently negative at 4 and37°C but was detected at room temperature (18–22°C). Atphysiologic temperatures, activated PBMCs showed intracellularaccumulation of the anti‐CD1c mAbs, indicating that CD1c cycled betweencell surface and intracellular compartments. The CD1c exocytosispathway was sensitive to Brefeldin A, cytochalasin B, andchloroquine.