Objective: To investigate the effects of hypoxia on T-lymphocyte expression of IL-2 messenger RNA (mRNA), after cell activation with phorbol ester and ionomycin.
Design: Prospective, controlled, cellular trial.
Setting: University research laboratory.
Subjects: EL4.6.1 cells, a murine T-cell lymphoma line.
Interventions: Tissue culture media was deoxygenated and flushed continuously with 100% helium to maintain a PO2 of 30 to 40 torr (< 40 torr [< 5.3 kPa]), or flushed with 10% oxygen/90% helium to maintain a PO2 of 45 to 55 torr (> 45 torr [> 6.0 kPa]). The pH was maintained between 7.3 and 7.6. The media was inoculated with EL4 cells. Aliquots of cells were obtained at intervals and divided into two groups: an immediate group, stimulated immediately, and an overnight group that was returned to normal incubator conditions of 5% CO2/humidified room air for 18 hrs before stimulation.
Measurements and main results: Gas tension, pH, cell count, and viability were determined for each aliquot. Cells were stimulated with phorbol myristate acetate and ionomycin for 4 hrs, at which time levels of interleukin-2 (IL-2) messenger RNA (mRNA) and gamma actin mRNA were measured by solution hybridization and enzyme immunoassay. The results were expressed as IL-2 mRNA/gamma actin mRNA ratio, normalised to baseline room air values. Cell viability and housekeeping functions (gamma actin mRNA expression) were unaffected by hypoxia. Cells exposed to a PO2 of < 40 torr (< 5.3 kPa) demonstrated a dramatic reduction in IL-2 mRNA expression with increasing duration of hypoxia. These effects persisted after an 18-hr recovery period. There was no effect on IL-2 mRNA expression when cells were exposed to a PO2 of > 45 torr (> 6.0 kPa).
Conclusions: The regulation of IL-2 transcription in the T lymphocyte appears to be exquisitely sensitive to changes in oxygen tension. Exposure to a PO2 of < 40 torr (< 5.3 kPa) causes prolonged impairment of IL-2 mRNA expression. IL-2 is an important growth factor for T and NK cells, and plays a pivotal role in the regulation of the host's immune response. The long-lasting effects of brief hypoxic exposure may, in part, explain the critically ill patient's predisposition to infectious complications.