Autoimmunity

Autoimmunity is the failure of the immune system to maintain self-tolerance, resulting in immune attack against the organism's own tissues. Rather than a single disease, autoimmunity is a breakdown mode of a complex adaptive system — the network of regulatory mechanisms that normally confines immune reactivity to foreign antigens loses its basin of attraction and settles into a pathological steady state.

The transition from tolerance to autoimmunity is rarely caused by a single genetic or environmental factor. Instead, it emerges from the interaction of susceptibility alleles, molecular mimicry (where pathogen antigens resemble self antigens), defective regulatory T cell function, and tissue damage that exposes previously sequestered self-antigens. Each factor is individually common; their coincidence is what pushes the system across a threshold. Autoimmunity is a systems-level phase transition, not a component-level malfunction.