Which of the following is (are) true regarding type III hypersensitivity reactions? Select all that apply. (NCLEX/HESI/TEAS)
a. They involve IgG.
b. They involve IgM.
c. They are considered delayed reactions.
d. They include autoimmune disorders like multiple sclerosis.
e. They are rare compared with type I reactions.

Verified step by step guidance

1. Understand that type III hypersensitivity reactions are immune complex-mediated reactions.
2. Recognize that these reactions typically involve the formation of immune complexes between antigens and antibodies, primarily IgG and sometimes IgM.
3. Note that these immune complexes can deposit in various tissues, leading to inflammation and tissue damage.
4. Consider that type III hypersensitivity reactions are not classified as delayed-type hypersensitivity; they are more immediate compared to type IV reactions.
5. Identify that autoimmune disorders like systemic lupus erythematosus (SLE) are classic examples of type III hypersensitivity, but multiple sclerosis is not typically classified under this category.

Key Concepts

Type III Hypersensitivity

Type III hypersensitivity reactions are immune responses that occur when antigen-antibody complexes form and deposit in tissues, leading to inflammation and tissue damage. These reactions are mediated primarily by IgG and IgM antibodies, which can trigger complement activation and attract leukocytes, resulting in local inflammation. Common examples include conditions like systemic lupus erythematosus and rheumatoid arthritis.

Delayed Reactions

Delayed hypersensitivity reactions, often associated with Type IV hypersensitivity, typically take hours to days to manifest. However, Type III reactions can also exhibit delayed characteristics due to the time required for immune complex formation and subsequent tissue damage. Understanding the timing of these reactions is crucial for differentiating them from immediate hypersensitivity responses.

Autoimmune Disorders

Autoimmune disorders occur when the immune system mistakenly attacks the body's own tissues. Type III hypersensitivity is implicated in several autoimmune diseases, such as multiple sclerosis and lupus, where immune complexes contribute to tissue injury. Recognizing the link between these hypersensitivity reactions and autoimmune conditions is essential for understanding their pathophysiology and clinical implications.