The study was performed to further elucidate the mechanisms of dysfunctional T-cell activation following extensive burn and mechanical injuries. The major regulatory level of interleukin-2 (IL-2) release under stressful conditions was determined via parallel analysis of IL-2 messenger RNA (mRNA) expression and IL-2 protein synthesis in mitogen-stimulated peripheral blood mononuclear cell (PBMCs) cultures on consecutive days postinjury. Furthermore, we wanted to scrutinize if inadequate lymphokine production after trauma is possibly a result of defective transduction of extracellular signals to the T-cell nucleus. Fourteen patients (11 men, 3 women, average age 38 +/- 6 years, injury Severity Score 34 +/- 2) were included in the study. The PBMCs were isolated on days 1, 3, 5, 7, and 10 and stimulated either with the mitogen phytohemagglutinin (PHA) alone or in combination with the protein kinase C (PKC) activator phorbol myristate acetate (PMA). The protein release was examined via bioassay (human con-A blasts) from the supernatants, and the cellular RNA was indicated by radioactive hybridization with the specific complementary DNA (cDNA) after Northern blotting. The IL-2 protein synthesis generated in PHA-stimulated PBMC cultures following trauma, compared with that in controls (0.62 +/- 0.04 U/mL) was persistently and significantly depressed during the observation time with a 57% inhibition on day 10-identical with that on day 1. The Northern blot analysis of IL-2 mRNA expression in the lysates of PHA-stimulated cell cultures after trauma could not detect any mRNA signal for IL-2, in contrast to the control cells. The addition of phorbol ester as a co-stimulus to the PBMC cultures of the trauma population induced very distinct mRNA signals for IL-2, with a signal intensity that was comparable with that found in the cells of healthy controls. The quantity of IL-2 protein generated from PBMC cultures of the trauma population on all days after trauma following PHA/PMA co-stimulation over 4 hours was identical with that of the control group (0.68 +/- 0.04 U/mL). We saw a considerable enhancement of IL-2 protein release following stimulation with phorbol esters during 20 hours, the degree of which was also identical between patients and controls (1.25 +/- 0.03 U/mL). The analysis of the corresponding profiles of IL-2 mRNA expression and IL-2 protein synthesis, which were documented for the individual patients, revealed a very close concurrence between the quality of gene expression and lymphokine production, and led us to conclude that the stress-induced alteration of IL-2 synthesis is regulated on the transcriptional level. The restoration of adequate IL-2 synthesis following injury evidently reflects the increase of mRNA for IL-2, and was accomplished through the administration of a co-stimulus PMA, a compound that mimicks the action of essential second messengers. From that finding, we further concluded that the expression of mRNA for IL-2 and IL-2 secretion following trauma is not constitutionally defective, but most likely attributable to alterations in the transmission of signals from the cell membrane to the nucleus. It remains to be determined, however, which of the substrates involved within the cascade of messengers are ultimately-under stressful conditions-responsible for the failure of IL-2 mRNA expression.