Regulation of cytokine production in aging: use of recombinant cytokines to upregulate mitogen-stimulated spleen cells

We investigated the production of IL-2 and IFN- γ (Th1 type) and IL-4 (Th2 type) cytokines by mitogen-activated spleen cells from young, adult and old mice. Cytokine production was evaluated in culture supernatants by CTLL proliferation (IL-2), ELISA (IFN- γ), CT4.S proliferation (IL-4) and in mRNA extracted from activated CD4+ cells by RT-PCR (IL-2, IFN- γ and IL-4). Results show that the production of IL-2, as protein and mRNA, is profoundly depressed by aging, whereas that of IFN- γ, as protein and mRNA, firstly declines and then increases with age. The production of IL-4, as protein, monotonically declines with aging whereas, as mRNA, firstly decreases and then increases above the level in young mice. Spleen cells in culture were also incubated with mitogens and with a recombinant cytokine (IL-1 β, IL-2, IL-3, IL-4, IL-12 or IFN- γ) at various concentrations. It was found that recombinant cytokines by and large enhance cytokine production when the level induced by mitogens only is low. This conclusion applies to IL-2 and IFN- γ production as protein and mRNA. The addition of recombinant cytokines also increases the production of IL-4 at the protein level in spleen cells from old mice but, at the mRNA level, only in spleen cells from young mice. This finding suggests age-related changes in IL-4-specific mRNA transcription rate and post-transcriptional half-life as well as translation kinetics.