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Impaired Interleukin-12-Dependent T-Cell Functions During Aging: Role of Signal Transducer and Activator of Transcription 4 (STAT4) and Suppressor of Cytokine Signaling 3 (SOCS3)

Department of Internal Medicine, Immunology and Infectious Diseases, Section of Internal Medicine, University of Bari Medical School, Italy.

Address correspondence to Cosimo Tortorella, MD, Department of Internal Medicine, Immunology and Infectious Diseases, Section of Internal Medicine, Policlinico, 70124 Bari, Italy. E-mail: c.tortorella{at}intmed.uniba.it

Interleukin (IL)-12 is the major inducer of T helper cell (Th) 1-type responses. Despite a higher IL-12 production, phytohemagglutinin (PHA)-stimulated peripheral blood mononuclear cells (PBMC), as well as CD4⁺ or CD8⁺ T cells from elderly donors released interferon (IFN)- amounts similar to those observed in young controls, and underwent only a slight increase in IFN- production after IL-12 costimulation. These findings were not due to an age-related reduction in IL-12 receptor expression. Interestingly, no difference in PHA-triggered signal transducer and activator of transcription 4 (STAT4) phosphorylation between young and elderly donors was found, and a significant IL-12-induced STAT4 activation occurred only in PHA-preactivated cells from the younger group. The age-related defect in IL-12 signaling was STAT4-restricted as it did not involve the p38 mitogen-activated protein kinase (MAPK) pathway. Finally, suppressor of cytokine signaling 3 (SOCS3) expression was significantly higher in unstimulated cells from elderly individuals, and it did not diminish after cell stimulation. These results indicate that a defective STAT4 activation, likely dependent on elevated SOCS3 levels, is involved in the impaired IL-12-dependent T-cell functions with aging.