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Aging is accompanied by chronic low-grade inflammation – a term which relates to increase in serum levels of cytokines such as interleukin 6 (IL-6), TNF-α and acute phase proteins such as C-reactive protein. Multiple studies in humans have shown that IL-6 most reliably increases with aging. Frailty is a geriatric syndrome characterized by decrease in physical ability and increased vulnerability to stressors. One of the most consistent findings in frail subjects is an elevation of serum IL-6 but we lack research which delineates is this a causational relationship. We developed a mouse model with inducible IL-6 expression (IL-6TET-ON/+ mice) that enables overexpression of IL-6 following stimulation with doxycycline (dox) administrated in food. IL-6 induction was dose dependent and led to increase in frailty as measured by 30-point murine clinical frailty index. Mice induced to express high levels of IL-6 quickly displayed an increase in frailty index, decrease in muscle grip strength and loss of fat. Mice induced to express 3–4 fold increase in IL-6 similar to frail humans displayed similar changes after months of induction. We measured IL-6 levels in serum and various tissues (gut, muscle, adipose, spleen) of aged (28-month-old) frail mice and adult controls as well as dox fed IL-6TET-ON/+ mice. We observed that IL-6 levels were increased in serums and spleen homogenates of aged mice and IL-6TET-ON/+ mice but not in other tissues. We determined that neutrophils were the main producers of IL-6 and their numbers were higher in spleens of aged and IL-6TET-ON/+ mice compared to adult controls. We conclude that elevated IL-6 serum levels are directly associated with age-related frailty and that spleen neutrophils are likely the main producers of IL-6.

The NOD mouse is an invaluable model for the study of autoimmune diabetes. Furthermore, although less appreciated, NOD mice are susceptible to other autoimmune diseases that can be differentially manifested by altering the balance of T cell costimulatory pathways. In this study, we show that constitutively expressing B7-1 on B cells (NOD-B7-1B-transgenic mice) resulted in reduced insulitis and completely protected NOD mice from developing diabetes. Furthermore, B7-1 expression led to a dramatic reduction of the B cell compartment due to a selective deletion of follicular B cells in the spleen, whereas marginal zone B cells were largely unaffected. B cell depletion was dependent on B cell specificity, mediated by CD8+ T cells, and occurred exclusively in the autoimmune-prone NOD background. Our results suggest that B cell deletion was a consequence of the specific activation of autoreactive T cells directed at peripheral self Ags presented by maturing B cells that expressed B7-1 costimulatory molecules. This study underscores the importance of B7 costimulatory molecules in controlling the amplitude and target of autoimmunity in genetically prone individuals and has important implications in the use of costimulatory pathway antagonists in the treatment of human autoimmune diseases.