Question

Which of the following induces a type III hypersensitivity? a. release of inflammatory molecules from mast cells b. accumulation of immune complexes in tissues and small blood vessels c. destruction of cells bound by antigens d. destruction of cells bound by antibodies

Short answer

b. accumulation of immune complexes in tissues and small blood vessels

Step-by-step solution

Identify Type III Hypersensitivity

Type III hypersensitivity is characterized by the immune response in which immune complexes (antigen-antibody complexes) accumulate in tissues and trigger an inflammatory response.

Match Hypersensitivity with Options

Review each option and determine which one aligns with the description of a type III hypersensitivity. Only one option should describe the accumulation of immune complexes.

Choose the Correct Option

Select the option that matches the description of Type III hypersensitivity, which involves the accumulation of immune complexes in tissues and small blood vessels.

Key concepts

Immune Complexes Accumulation

When the body's immune system detects a foreign substance—a virus, bacteria, or even a non-living material—it often responds by producing antibodies that attach to the invader, forming complexes. In a typical immune reaction, these so-called 'immune complexes' are swiftly cleared away by immune cells. However, in Type III hypersensitivity, which includes disorders like systemic lupus erythematosus and rheumatoid arthritis, these complexes tend to accumulate.

This accumulation occurs because the body produces a robust amount of antibodies or because the complexes form quickly in large quantities that the body cannot eliminate effectively. They primarily deposit in tissues and small blood vessels, obstructing normal functions and leading to further complications such as tissue damage. This process begins with the interaction of an antigen with an antibody, primarily the IgG type, to form immune complexes that unfortunately do not clear as intended.

Inflammatory Response

The accumulated immune complexes that characterize Type III hypersensitivity trigger a series of reactions within the body known as the inflammatory response. This is the body's attempt to remove the complexes, but it often causes more harm than good.

When immune complexes settle in tissues, they activate complement proteins, which are a part of the immune system designed to combat infections. This activation results in the production of inflammatory molecules, such as chemokines and cytokines, which signal other immune cells to the site of the immune complex deposition. The arrival of immune cells, notably phagocytes like neutrophils, is intended for clearance but often leads to tissue damage. They release enzymes and reactive oxygen species meant to destroy pathogens, but when misdirected, they harm the body’s own cells.

Hypersensitivity Reactions

Hypersensitivity reactions are exaggerated or inappropriate responses of the immune system to an antigen or perceived threat. These responses can be immediate, as seen in allergies, or delayed, typically occurring hours to days after exposure to the antigen.

Type III hypersensitivity is one such delayed reaction, where the immune system, instead of protecting, inadvertently harms tissue through complex-mediated immune responses. It is differentiated from Type I (immediate and often allergic reactions mediated by IgE) and Type II (cytotoxic hypersensitivity where antibodies target cells with specific antigens) hypersensitivity reactions. Unlike Type I, which involves mast cells and basophils, Type III is solely focused on the antigen-antibody complex impact on tissues and cells, not directly involving cell destruction by antibodies or release of inflammatory molecules from mast cells. These complex-mediated issues are the hallmark of diseases like serum sickness and certain forms of glomerulonephritis, where understanding the underlying immune dysfunction is crucial for accurate diagnosis and appropriate treatment.