Dissociation of phosphoinositide hydrolysis and Ca²⁺ fluxes from the biological responses of a T-cell hybridoma

Abstract

T lymphocytes can be activated in a variety of ways, including occupancy of the T cell antigen receptor (TCR) complex or cross-linking of certain cell-surface molecules with antibody^1–4. Two of the earliest events seen after stimulation are the hydrolysis of phosphatidylinositol bisphosphate to inositol trisphosphate (Ins P₃) and 1,2-diacylglycerol (DAG)^5–7, and an increase in the concentration of intracellular Ca²⁺ ([Ca²⁺]_i)^8–11. Later, the cell secretes lymphokines and expresses lymphokine receptors¹. It has been postulated that the products of the hydrolysis of phosphatidylinositols (Ptd Ins) and fluctuations in [Ca²⁺]_i are critical 'second messengers≈, transmitting the signals for the initiation of the later events. We have examined the relationship between these second messengers and the secretion of IL-2 in a murine T cell variant whose missing TCR complex had been reconstituted by gene transfer. Surprisingly, although the IL-2 responses of the transfectant could not be distinguished from the original line expressing the same TCR, Ptd Ins hydrolysis and the increase in [Ca²⁺]_i were substantially reduced or absent in the reconstituted cell. It is therefore possible to dissociate these early biochemical changes from a late biological response, raising questions about the putative causal relationship of these events.