DYNAMIC ADHESION OF CD8-POSITIVE CELLS TO ANTIBODY-COATED SURFACES - THE INITIAL STEP IS INDEPENDENT OF MICROFILAMENTS AND INTRACELLULAR DOMAINS OF CELL-BINDING MOLECULES

Cell adhesion is a multistep, metabolically active process usually req uiring several minutes or even hours to complete. This results in the formation of strong bonds that cannot be ruptured by mechanical forces encountered by living cells in their natural environment. However, th e first seconds after contact formation are much more sensitive to ext ernal conditions and may be the critical step of adhesion. This step i s very difficult to monitor without disturbing the observed system. We addressed this problem by studying the interaction between anti-CD8-c oated or control surfaces and murine lymphoid cell lines bearing wild- type CD8 molecules, or genetically engineered molecules bearing extrac ellular CD8 domains and transmembranar and intracytoplasmic domains of class I histocompatibility molecules, or with extensive deletion of i ntracytoplasmic domains. We used a new method that consisted of monito ring the motion of cells driven along adhesive surfaces by a hydrodyna mic force weaker than the reported strength of single ligand-receptor bonds, but sufficient to make free cells move with an easily detectabl e velocity of several micrometers per second. Cells exhibited short-te rm (less than or equal to 0.5 s) adhesions to the surface with a frequ ency of about one event per 30-s period of contact. These events did n ot require specific antigen-antibody bonds. However, when anti-CD8 wer e present, strong adhesion was achieved within <1 s, since most arrest s were longer than a standard observation period of 1 min. This bond s trengthening was not affected by cytochalasin, and it did not require intact intracellular domains on binding molecules. It is concluded tha t the initial step in strong adhesion may be viewed as a passive, diff usion-driven formation of a new specific bonds.