ANTIBODY-INDUCED MODULATION OF CD26 SURFACE EXPRESSION

The ability of different anti-CD26 monoclonal antibodies to modulate t he expression of CD26 on human T lymphocytes was investigated. By mean s of a new non-radioactive method using fluorescein isothiocyanate (FI TC)-labelled and unlabelled anti-CD26 monoclonal antibodies and flow c ytometry, we measured the internalization and re-expression of CD26 on freshly isolated resting human T lymphocytes. The modulation of CD26 surface expression takes place in primarily CD26(+) as well as in CD26 (-) T lymphocytes, indicating the presence of an intracellular CD26 po ol. In fact, with two different anti-CD26 monoclonal antibodies (Ta1 a nd M5) intracellular CD26 was detected out of which newly expressed CD 26 might have originated. This intracellular CD26 pool appears to be m aintained by continuous translation of CD26 mRNA.