What type of hypersensitivity reaction is systemic lupus erythematosus (SLE)?

Systemic lupus erythematosus (SLE) is classified as a Type III hypersensitivity reaction. This type of hypersensitivity is characterized by the formation of immune complexes, which are aggregates of antibodies and antigens. In the case of SLE, autoantibodies target various nuclear components such as DNA, histones, and ribonucleoproteins.

These autoantibody-antigen complexes circulate in the bloodstream and can deposit in various tissues, including the skin, kidneys, and joints, leading to inflammation and tissue damage. This deposition triggers an inflammatory response mediated by the complement system and various immune cells, further exacerbating the symptoms of the disease.

Understanding the mechanisms involved in Type III hypersensitivity is crucial for recognizing how SLE manifests in different organs and helps explain the diverse clinical features that can occur, such as glomerulonephritis and skin rashes. This differs from other types of hypersensitivity; for instance, Type I involves IgE-mediated responses, Type II is related to antibody-mediated cell destruction, and Type IV is a delayed-type reaction predominantly mediated by T cells, none of which are the underlying mechanism in SLE.