IFNG and diphtheria: Pro-inflammatory cytokines such as IL-15 and IL-6 increase in the bone marrow of older adults, along with CD8+ CD28- accumulation and CD8+CD69+ T cells which produce interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α), plus other pro-inflammatory cytokines.23,24 Concomitantly, there is a significant reduction of total and antigen-specific plasma cells with age, for example those against tetanus and diphtheria.