The function of immune cells is dependent upon a constant and adequate supply of energy (ATP), which is mainly formed by oxidative phosphorylation (OXPHOS). In arthritis, microenvironmental conditions are characterized by low levels of oxygen and glucose. Thus, effector cells of the innate immune system are recruited to sites where they face an acute need to respond to these demanding conditions. We investigated how immune cells maintain viability and function under these circumstances, and which immune processes are limited to what extent by energy deficiency.

From peripheral mononuclear cells obtained from healthy donors, we isolated CD4⁺ T-cells (MACS, > 98% purity) and incubated them (37°C, 5% CO2) in RPMI 1640 with 11.1 mmol/l glucose (permits OXPHOS and glycolysis) and without glucose (permits OXPHOS only). As a measure of oxidative ATP formation, cellular oxygen consumption was determined amperometrically with a Clark electrode. Under the conditions of unaffected ATP production and ATP production inhibited stepwise using myxothiazole, PMA/ionomycin-stimulated cytokine production (IL-2, IL-4, IFN-γ, TNF-α, 6 hours) and anti-CD3-/anti-CD28-stimulated proliferation (over 96 hours) were quantified.

In the glucose-containing medium, both stimulated cytokine production and proliferation were unaffected, even under complete suppression of OXPHOS. Only when OXPHOS and glycolysis were suppressed simultaneously and almost completely were cytokine production and proliferation significantly decreased.

We have quantified the energy requirement of specific immune functions in human CD4⁺ T cells. Under maximally inhibited OXPHOS, glycolysis fully compensates for the ATP supply for the energy requirements of the immune functions investigated. These data demonstrate a high adaptive potential of CD4⁺ T cells to maintain specific immune functions even under massively impaired energetic conditions.