A Molecular Mechanism for TNF-α-Mediated Downregulation of B Cell Responses

B cell function with age is decreased in class switch recombination (CSR), activation-induced cytidine deaminase (AID), and stability of E47 mRNA. The latter is regulated, at least in part, by tristetraprolin (TTP), which is increased in aged B cells and also negatively regulates TNF-alpha. In this study, we investigated whether B cells produce TNF-alpha, whether this changes with age, and how this affects their function upon stimulation. Our hypothesis is that in aging there is a feedback mechanism of autocrine inflammatory cytokines (TNF-alpha) that lowers the expression of AID and CSR. Our results showed that unstimulated B cells from old BALB/c mice make significantly more TNF-alpha mRNA and protein than do B cells from young mice, but after stimulation the old make less than the young; thus, they are refractory to stimulation. The increase in TNF-alpha made by old B cells is primarily due to follicular, but not minor, subsets of B cells. Incubation of B cells with TNF-alpha before LPS stimulation decreased both young and old B cell responses. Importantly, B cell function was restored by adding anti-TNF-alpha Ab to cultured B cells. To address a molecular mechanism, we found that incubation of B cells with TNF-alpha before LPS stimulation induced TTP, a physiological regulator of mRNA stability of the transcription factor E47, which is crucial for CSR. Finally, anti-TNF-alpha given in vivo increased B cell function in old, but not in young, follicular B cells. These results suggest new molecular mechanisms that contribute to reduced Ab responses in aging. The Journal of Immunology, 2012, 188: 279-286.