Membrane trafficking of CD1c on activated T cells

We investigated the regulation of and the intracellular trafficking involve d in the membrane expression of CD1c antigen on activated mature T cells. M embrane expression of this glycoprotein was highly regulated and dependent on the activation state of the cells. The presence of the CD I c antigen on activated peripheral blood mononuclear cells (PBMCs) was confirmed by flow cytometry, reverse transcriptase-PCR (RT-PCR), and immunoperoxidase staini ng. The RT-PCR analysis of the alpha3- and 3'-untranslated regions of CD1C showed that phytohemagglutinin (PRA) activation induced expression of trans cripts that encode the three isoforms (soluble, membrane, and cytoplasmic/s oluble). Immunocytochemical studies showed a specific association of CD I c with the cell membrane and a cytoplasmic, perinuclear distribution. Althou gh flow-cytometric staining confirmed the intracellular presence of CD1c, m embrane expression on PHA blast cells was not detected. We found that membr ane detection of CD1c antigen was temperature dependent. Cell surface bindi ng of the anti-CD1c monoclonal antibody (mAb) was consistently negative at 4 and 37 degreesC but was detected at room temperature (18-22 degreesC). At physiologic temperatures, activated PBMCs showed intracellular accumulatio n of the anti-CD1c mAbs, indicating that CD1c cycled between cell surface a nd intracellular compartments. The CD1c exocytosis pathway was sensitive to Brefeldin A, cytochalasin B, and chloroquine.