Immune Aging in Rheumatoid Arthritis

Abstract

Rheumatoid arthritis (RA) is a life-long autoimmune disease caused by the confluence of genetic and environmental variables that lead to loss of self-tolerance and persistent joint inflammation. RA occurs at the highest incidence in individuals >65 years old, implicating the aging process in disease susceptibility. Transformative approaches in molecular immunology and in functional genomics have paved the way for pathway paradigms underlying the replacement of immune homeostasis with auto-destructive immunity in affected patients, including the process of immune aging. Patients with RA have a signature of premature immune aging, best understood for CD4⁺ T cells which function as pathogenic effectors in this HLA class II-associated disease. Premature immune aging is present in healthy HLA-DRB1*04⁺ individuals, placing accelerated immune aging prior to joint inflammation. Aging-related molecular abnormalities directly implicated in turning RA CD4⁺ T cells into pro-inflammatory effector cells are linked to malfunction of subcellular organelles, such as mitochondria, lysosomes, lipid droplets and the endoplasmic reticulum. Resulting changes in T cell behavior include cellular hypermobility; tissue invasiveness; unopposed mTORC activation; excessive release of tumor necrosis factor α (TNF); lysosomal failure; clonal expansion and immunogenic cell death. Aged and metabolically reprogrammed T cells in RA patients are accompanied by age-associated B cells (ABC), which specialize in autoantibody production. Clonal hematopoiesis drives myeloid cell aging by producing aged monocytes and hypermetabolic macrophages (Mϕ) that sustain the process of inflammaging. Here, we synthesize insights into the relationship of RA risk and immune aging and discuss mechanisms through which immune aging can cause autoimmunity.