In systemic lupus erythematosus, soluble antigens and antibodies precipitate along blood vessel linings. Which hypersensitivity type is this?

1. Four types of hypersensitivity are used to sort these over-reactions, with the first three mediated by B cells and the fourth by T cells. 2. Type I is immediate hypersensitivity, driven by allergen-specific IgE crosslinked on the mast cell surface. 3. Type II involves IgG-mediated lysis of cells by complement proteins, as in mismatched blood transfusions. 4. Type III occurs when soluble antigens, mostly DNA and other material from the nucleus, and antibodies accumulate in the blood and precipitate along blood vessel linings. 5. Those immune complexes lodge in the kidneys, joints and other organs, where they activate complement proteins and cause inflammation. 6. Systemic lupus erythematosus is the named example of that mechanism, so the answer is type III. 7. Type IV is the delayed cellular reaction of the tuberculin test, which recruits macrophages instead of depositing complexes. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 21 "The Lymphatic and Immune System", section 21.6 Diseases Associated with Depressed or Overactive Immune Responses_