IL-2 modulates IFNγ mRNA gene expression in cultured peripheral blood mononuclear cells from septic patients

Introduction

IL-2 activates numerous key cells in the immune system [1]. We have previously demonstrated that IFNγ mRNA gene expression in peripheral blood mononuclear cells (PBMC) is downregulated in patients with sepsis compared with healthy controls [2]. Here we investigated IFNγ gene expression in cultured PBMC from healthy controls and patients with severe sepsis and examined whether exogenous IL-2 can influence IFNγ mRNA expression.

Methods

PBMC were isolated from five healthy controls and five patients with severe sepsis and were cultured in 24-well plates. Cells were incubated in medium alone or stimulated with either 1 μg/ml lipopolysaccharide (LPS) for 24 hours (activate monocytes and B cells), 3 μg/ml anti-CD3 (mAb) for 4 hours (activate T cells), or 10 ng/ml phorbol myristate acetate (PMA) + 1 μM ionomycin for 4 hours (activate all cells). Each experiment was performed in the absence and presence of 50 U recombinant IL-2 (rIL-2). Total RNA was isolated and reverse transcribed. IFNγ mRNA gene expression was quantified with quantitative RT-PCR. Results were analysed with ANOVA and the t test where appropriate.

Results

IFNγ mRNA production is lower in PBMC of patients with sepsis compared with healthy controls (P = 0.03) but similar when measured in the presence of rIL-2. With T-cell stimulation, IFN mRNA was greater in PBMC from septic patients compared with controls (P = 0.02) but similar in the presence of rIL-2. With LPS stimulation of monocytes and B cells, IFNγ mRNA was lower in PBMC from septic patients compared with controls (P = 0.02), but similar in the presence of rIL-2. With PMA stimulation, IFNγ mRNA was similar in PBMC from septic patients and controls in the presence and absence of rIL-2.

Conclusion

IFNγ mRNA production is reduced in PBMC in sepsis but can be stimulated ex vivo to produce normal IFNγ levels In the absence of rIL-2, IFNγ mRNA production is inducible in T cells but not in monocytes and B cells. IL-2 modulation of IFN mRNA production appears to be stimulus dependent, and may contribute to the host defence mechanism.