Which of the following explains the difference between type II and type III hypersensitivity reactions?

Which of the following explains the difference between type II and type III hypersensitivity reactions?

• A. Type II involves cellular antigens.
• B. Type III involves IgE.
• C. IgG is involved only in type III reactions.
• D. Type II reactions involve no antibody.

Answer: (A)

The key idea is how the antibodies cause damage in these two reactions. Type II hypersensitivity is antibody-mediated cytotoxicity: antibodies (usually IgG or IgM) bind to antigens on the surface of cells or in the extracellular matrix, marking those cells for destruction or dysfunction. This direct targeting of cellular antigens is why the correct statement says type II involves cellular antigens. In contrast, type III hypersensitivity is driven by immune complexes formed between antibodies and soluble antigens that deposit in tissues. These deposits trigger inflammation by activating complement and attracting neutrophils, but the damage is due to immune complex deposition rather than antibodies binding to cell surfaces. That’s why the other options don’t fit: type III does not specifically involve IgE (that’s typical of type I), IgG is involved in both type II and type III, and type II is not devoid of antibody—it is defined by antibody-mediated effects.

The key idea is how the antibodies cause damage in these two reactions. Type II hypersensitivity is antibody-mediated cytotoxicity: antibodies (usually IgG or IgM) bind to antigens on the surface of cells or in the extracellular matrix, marking those cells for destruction or dysfunction. This direct targeting of cellular antigens is why the correct statement says type II involves cellular antigens.

In contrast, type III hypersensitivity is driven by immune complexes formed between antibodies and soluble antigens that deposit in tissues. These deposits trigger inflammation by activating complement and attracting neutrophils, but the damage is due to immune complex deposition rather than antibodies binding to cell surfaces.

That’s why the other options don’t fit: type III does not specifically involve IgE (that’s typical of type I), IgG is involved in both type II and type III, and type II is not devoid of antibody—it is defined by antibody-mediated effects.