Interrelationship between signals transduced by phytohemagglutinin and interleukin 1

In the murine cell line LBRM‐331A5, phytohemagglutinin (PHA) induces secretion of the T cell growth factor interleukin 2 (IL2). IL1 augments PHA‐induced IL2 production. In this cell line, PHA stimulates a number of biochemical changes including phospholipid hydrolysis, increases in cytosolic free calcium ([Ca²⁺]_i), membrane hyperpolarization, cytosolic alkalinization, and tyrosine phosphorylation of specific substrates. Using LBRM cells, we have studied the interrelationship between these events and the secretion of IL2. Increases in [Ca²⁺]_i triggered by PHA or following addition of ionomycin result in membrane hyperpolarization but are not required for PHA‐induced cytosolic alkalinization or tyrosine phosphorylation. Addition of IL1 to PHA‐stimulated cells did not affect any of the biochemical parameters, although it significantly augmented PHA‐induced IL2 secretion. Increasing [Ca²⁺]_i with ionomycin did not trigger IL2 secretion, increases in cytosolic pH, or tyrosine phosphorylation in the presence or absence of IL1. Preventing increases in cytosolic pH did not alter PHA‐induced changes [Ca²⁺]_i in or membrane potential. These data are compatible with PHA including activation of phospholipase C and production of inositol phosphates resulting in both release of Ca²⁺ from internal stores and transmembrane uptake of Ca²⁺ as well as activation of protein kinase C. However, unlike other growth factor or mitogen‐stimulated systems, the changes stimulated by PHA and IL1 in LBRM cells including IL2 secretion are not regulated by a pertussis toxin‐sensitive G protein.