In type II hypersensitivity, antibodies target which of the following?

In type II hypersensitivity, antibodies target which of the following?

• A. Against cell surface or extracellular matrix antigens
• B. Against soluble antigens forming immune complexes
• C. Against intracellular pathogens
• D. Against mucosal IgE

Answer: (A)

In type II hypersensitivity, antibodies act directly on antigens that are exposed on the surface of cells or on extracellular matrix components. When these antibodies (usually IgG or IgM) bind to those surface or matrix antigens, they trigger effector mechanisms such as complement activation, opsonization leading to phagocytosis, or antibody-dependent cellular cytotoxicity by natural killer cells. This is why this type is described as antibody-mediated cytotoxic or cytotoxic-like. Examples include antibodies against blood group antigens on red blood cells (causing transfusion or hemolytic reactions) and autoimmune diseases like autoimmune hemolytic anemia or Goodpasture syndrome, where antibodies target basement membrane components. Against soluble antigens forming immune complexes is characteristic of type III hypersensitivity, not type II. Targeting intracellular pathogens isn’t the primary role of circulating antibodies in this context, since antibodies mainly interact with antigens accessible on cell surfaces or within the extracellular matrix. Mucosal IgE and type I hypersensitivity involve IgE-mediated mast cell activation, not this cell-surface–antigen–directed, antibody-mediated cytotoxic process.

In type II hypersensitivity, antibodies act directly on antigens that are exposed on the surface of cells or on extracellular matrix components. When these antibodies (usually IgG or IgM) bind to those surface or matrix antigens, they trigger effector mechanisms such as complement activation, opsonization leading to phagocytosis, or antibody-dependent cellular cytotoxicity by natural killer cells. This is why this type is described as antibody-mediated cytotoxic or cytotoxic-like.

Examples include antibodies against blood group antigens on red blood cells (causing transfusion or hemolytic reactions) and autoimmune diseases like autoimmune hemolytic anemia or Goodpasture syndrome, where antibodies target basement membrane components.

Against soluble antigens forming immune complexes is characteristic of type III hypersensitivity, not type II. Targeting intracellular pathogens isn’t the primary role of circulating antibodies in this context, since antibodies mainly interact with antigens accessible on cell surfaces or within the extracellular matrix. Mucosal IgE and type I hypersensitivity involve IgE-mediated mast cell activation, not this cell-surface–antigen–directed, antibody-mediated cytotoxic process.