Systemic lupus erythematosus (SLE) primarily involves which type of hypersensitivity reaction?

SLE is a prototype Type III hypersensitivity disease. In SLE, autoantibodies (anti-dsDNA, anti-Sm, anti-phospholipid) form immune complexes with self-antigens. These complexes deposit in tissues (kidneys, joints, skin, blood vessels) and activate the complement cascade, leading to inflammation and tissue damage. Manifestations include the butterfly rash, glomerulonephritis, serositis, and arthritis. Oral manifestations include ulcers and the lupus erythematosus (LE) cell. SLE can also involve Type II mechanisms (autoantibodies against blood cells causing hemolytic anemia, thrombocytopenia), but Type III is the predominant classification.