ABSTRACT
We have examined intracellular biochemical and metabolic changes induced by antibodies specific for glycosylphosphatidylinositol (GPI)-anchored cell surface molecules. In lymphoid cells the earliest detectable responses are phosphorylation of intracellular substrates. The GPI-linked target antigens are also rapidly redistributed into patches and caps on the cell surface and then internalised. Between two and five hours later, cytokine receptors are expressed. Later, cells become metabolically active and begin to proliferate and express endogenous cytokines, thus promoting autocrine growth. Very early events, such as kinase activity, are induced by antibody binding alone and are characteristic of the cell surface molecule recognised by antibodies. Thus, the initial events in the activation cascade are critical in selecting the metabolic route. Progression down the activation cascade requires further signals such as cross-linking antibodies, exogenous cytokines, phorbol esters, or accessory cells. Once in cycle, cells no longer display evidence of their original route of activation. Activated T lymphocytes acquire resitance to cleavage by GPI-specific phospholipase C, suggesting a possible feedback mechanism to limit cell proliferation