The requirement for lymphocyte function-associated antigen 1 in homotypic leukocyte adhesion stimulated by phorbol ester.

Abstract

Lymphocytes become adherent and aggregate after stimulation with phorbol esters such as PMA. Time-lapse video showed that aggregating cells were motile and exhibited vigorous pseudopodial movements. Adhesion sites were initiated between pseudopodia of neighboring cells, and then moved to the uropod. PMA-stimulated aggregation by EBV-transformed B cell lines, SKW-3 (a T cell line), differentiated U937 (a monocytic line), and blood lymphocytes was inhibited by mAbs to LFA-1. A number of different mAb to the LFA-1 alpha and beta subunits and F(ab')2 and Fab' fragments inhibited aggregation. Furthermore, lymphoblasts from normal individuals, but not from LFA-1-deficient patients, aggregated in response to PMA. These findings suggest LFA-1 is critically involved in stimulated lymphocyte adhesion. LFA-1 expression was not increased by PMA stimulation, showing that other mechanisms regulate LFA-1-dependent adherence. LFA-1-deficient patient cells were able to coaggregate with LFA-1+ cells, showing that aggregation is not mediated by like-like interactions between LFA-1 molecules on opposite cells. Aggregation was Mg+2-dependent, inhibited by cytochalasin B, and was reversed when LFA-1 mAb was added to preformed aggregates. Previous findings suggesting that LFA-1 is important in a wide variety of leukocyte functions are elucidated by this work, which shows that LFA-1 is a general leukocyte cell adhesion molecule, the activity of which is regulated by cell activation.

The Number of Responding CD4 T Cells and the Dose of Antigen Conjointly Determine the Th1/Th2 Phenotype by Modulating B7/CD28 Interactions

“…It is becoming better appreciated that, during the course of their activation, T cells form substantial homo-and heterotypic clusters around the activating APC and that direct T cell-T cell signaling occurs within these clusters (52)(53)(54)(55)(56). In the context of our study, we believe that critical CD28-B7 interactions may be occurring within these T cell clusters.…”

NF-κB inhibition causes spontaneous apoptosis in Epstein–Barr virus-transformed lymphoblastoid cells

“…An early effect of growth in Tc Ϫ media was that the cells no longer grew in aggregates. Homotypic adhesion of LCLs is because of lymphocyte function-associated antigen 1 and ICAM-1 (48,49), and ICAM-1 expression can be regulated by NF-B (50). FACS analysis revealed a 2-fold decrease in ICAM-1 expression on cells grown in Tc Ϫ media (Fig.…”

A Single Amino Acid in the Cytoplasmic Domain of the β2 Integrin Lymphocyte Function-associated Antigen-1 Regulates Avidity-dependent Inside-out Signaling

“…Activation of LFA-1 is required for efficient binding to its ligand ICAM-1. The addition of the phorbol ester PMA has been shown to activate LFA-1 on leukocytes (10). When wild type LFA-1 is transfected into the erythroleukemic cell line K562 (K562-␣ L /␤ 2 ) (Figs.…”

“…Inside-out signals are initiated upon triggering of specific cell surface molecules, generating intracellular signals that induce a high affinity and/or avidity state of LFA-1 (9). Both conformational changes (affinity) in the presence of Mg 2ϩ and altered surface distribution of LFA-1 into clusters (avidity) upon Ca 2ϩ binding result in strong ligand binding (8,10,11). Although the ␣ L and ␤ 2 cytoplasmic domains of LFA-1 are relatively short and do not contain any intrinsic kinase activity, they are important for affinity and avidity regulation.…”