Hypersensitivity Immune Responses

Hypersensitive Immune Responses

Overview: This lecture covers hypersensitive immune responses, which are a set of conditions where the immune system overreacts to a particular stimulus. It is broken into four types and discusses the antigen, immune component, mechanism, and disease examples for each type.

Type 1 (IgE-Mediated):

• Antigen: Freely moving, such as pollen, venom, or proteins in peanuts.

• Immune Component: Antibody called IgE.

• Mechanism: The antigen is picked up by a B cell, which releases IgE antibodies that stick to mast cells. On the second exposure, the antigen binds to the antibodies and mast cells, releasing histamine and causing inflammation.

• Disease Examples: Allergic asthma, anaphylaxis.

• Mnemonic: AOK (Asthma, Allergies, Anaphylaxis).

Type 2 (Cytotoxic):

• Antigen: Fixed on the cell, such as blood type antigens.

• Immune Component: Antibody called IgG.

• Mechanism: If there is a mismatch between the antigen and antibody, the antibody will bind to the antigen and cause a complement response, leading to death of the cell.

• Disease Examples: Hemolytic disease of the newborn, transfusion reactions.

• Mnemonic: HDN (Hemolytic Disease of the Newborn).

Inflammatory Responses

Overview: This section covers inflammatory responses, such as hemolytic anemia and Goodpasture Syndrome, which can be caused by transfusion incompatibility.

Goodpasture Syndrome

• Goodpasture Syndrome is caused by an antigen on the cell in the kidney that reacts with an antibody (IgG or IgM).

• This reaction triggers a complement response, which kills off the cells in the glomerulus and causes nephritis.

Immune Complex Response

Overview: This section covers immune complex responses, which occur when an antigen from a bacterial infection meets up with an antibody to form an immune complex.

• The antigen and antibody form an immune complex, which can bind to certain tissues and cause inflammation.

• Examples of this type of response include host strep glomerular nephritis and systemic lupus erythematosus (SLE).

Delayed Type Response

Overview: This section covers delayed type responses, which are driven by lymphocytes rather than antibodies.

• In this type of response, a macrophage takes up an antigen and presents it on its membrane, which causes a T helper cell to become sensitized.

• The T helper cell then releases cytokines, which bring more macrophages to the area and cause dermatitis.

• Examples of this type of response include contact dermatitis (e.g. latex) and type 1 diabetes.