Cytolysin A (ClyA) is a newly discovered cytolytic protein of Escherichia coli K-12 that mediates a hemolytic phenotype. We show here that highly purified ClyA and ClyA-expressing E. coli were cytotoxic and apoptogenic to fresh as well as cultured human and murine monocytes/macrophages.

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Human lymphocytes, freshly isolated from blood, were allowed to settle on surfaces coated by collagen type 1, fibronectin, laminin, IgG or albumin at different concentrations. In separate cultures the lymphocytes were also exposed to these proteins in soluble form. The lymphocytes, predominantly T cells, attached to two-dimensional collagen substrata both in the presence and absence of serum but did not adhere or adhered poorly to substrata coated with fibronectin, laminin, IgG and albumin. In contrast, T blasts induced in a mixed lymphocyte culture adhered to fibronectin-coated substratum. During contact with substratum-bound collagen for a 24-h period, 47 +/- 15% of the freshly purified lymphocytes from separate individuals developed motile behavior whereas 16 +/- 4% of the cells became motile on fibronectin. Gelatin (denatured collagen) also mediated attachment of lymphocytes to surfaces but only at comparatively high concentrations (40 mg/ml). Collagen and gelatin in solution also caused agglutination and motility of the vast majority of freshly isolated T lymphocytes whereas fibronectin and other proteins, when presented in soluble form, did not. Cell agglutination was maximal at moderate (10 or 20 mg/ml) and cell motility at low gelatin concentrations (1 to 10 mg/ml). High gelatin concentrations (20 and 40 mg/ml) did not induce motile behavior. Cytochalasin B augmented the proportion of adherent cells on gelatin-coated substrata. In the presence of cytochalasin B gelatin mediated substrate-adhesion at concentrations below those which normally induced adhesion indicating that motile behavior counteracted persistent lymphocyte adhesion to the substratum. Noteworthy, gelatin/collagen is unique among ligands (e.g. plasma fibronectin and other serum proteins) in its capacity to induce motility in the vast majority of resting lymphocytes freshly isolated from blood within a relatively short period. Taken together these results indicate that circulating lymphocytes have a collagen/gelatin-binding plasma membrane component. Cross-linking of this component is a likely explanation for the selective inducing effect of gelatin and collagen on lymphocyte motility. The present results showed that the lymphocyte plasma membrane contains collagen-binding components with a relative molecular mass of 130 and 55 kDa. The 55-kDa component also reacted with an anti-fibronectin antibody. Thus, interactions with the extracellular matrix may control lymphocyte locomotor capacity.

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The mechanisms controlling the formation of pseudopodia and other active cell edges in T lymphocytes are not understood. We show here that T lymphocytes express thrombospondin-1 (TSP-1). TSP-1 in T lymphocytes has a high turnover as shown by the fact that brefeldin and monensin rapidly increase while cycloheximide tend to decrease the cellular TSP-1 content. T cell TSP-1 is preferentially stored intracellularly and shows variable cell surface expression. T lymphocyte adhesion to fibronectin and collagen type IV induces TSP-1 expression on the cell surface via a brefeldin sensitive mechanism. A monoclonal antibody to TSP-1 inhibits the flattening and pseudopodia formation of the adherent T cells. Furthermore, the same antibody to TSP-1 also exerts an inhibitory effect on T cell migration in the absence of exogenous TSP-1. These results indicate that endogenous TSP-1 is part of an adhesion-dependent mechanism controlling cytoplasmic spreading and migration in T lymphocytes.