Question

Which one of the following is not an example of a type IV hypersensitivity? a. latex allergy b. Contact dermatitis (e.g., contact with poison ivy) c. a positive tuberculin skin test d. hemolytic disease of the newborn

Short answer

d. hemolytic disease of the newborn

Step-by-step solution

Understand Type IV Hypersensitivity

Type IV hypersensitivity is a delayed-type immune response mediated by T cells rather than antibodies. It typically occurs 24-72 hours after exposure to the antigen.

Analyze Each Option

Evaluate each option to determine if it aligns with the characteristics of type IV hypersensitivity.

Evaluate Option (a): Latex Allergy

Latex allergy is typically an immediate hypersensitivity (type I), mediated by IgE antibodies and occurring within minutes of exposure. Therefore, it is not an example of type IV hypersensitivity.

Evaluate Option (b): Contact Dermatitis

Contact dermatitis, such as that caused by poison ivy, is a classic example of type IV hypersensitivity. T cells are sensitized and cause a reaction 24-72 hours after contact.

Evaluate Option (c): Positive Tuberculin Skin Test

A positive tuberculin skin test is also an example of type IV hypersensitivity. It involves a delayed response by sensitized T cells to the tuberculin antigen.

Evaluate Option (d): Hemolytic Disease of the Newborn

Hemolytic disease of the newborn is an example of type II hypersensitivity, which involves antibody-mediated cell destruction. It does not fit the T-cell mediated response of type IV hypersensitivity.

Identify the Correct Answer

The option that does not fit the criteria for type IV hypersensitivity is (d) hemolytic disease of the newborn.

Key concepts

Immune Response

The human immune system is an intricate network designed to protect the body against harmful agents like bacteria, viruses, and toxins. The immune response is the body's way of identifying and eliminating these foreign invaders. There are two main types of immune responses: innate and adaptive. The innate immune system is the body's first line of defense and responds the same way to all types of threats. The adaptive immune system is more specialized and can remember specific pathogens for quicker responses in the future. T cells play a crucial role in the adaptive immune response.

T Cells

T cells, or T lymphocytes, are a type of white blood cell central to immune response. They develop in the thymus and have various roles depending on their type. There are two main types of T cells:

• Helper T cells (Th cells): These cells help activate other immune cells by releasing signaling molecules called cytokines.
• Cytotoxic T cells (Tc cells): These cells directly attack and kill infected or damaged cells.

T cells are critical for cell-mediated immunity, which involves the direct targeting of infected or abnormal cells.

Delayed-Type Hypersensitivity

Delayed-type hypersensitivity (DTH), also known as Type IV hypersensitivity, is a specific immune response that occurs late, typically 24-72 hours after exposure to an antigen. This type of hypersensitivity is mediated by T cells rather than antibodies.
In DTH, T cells become sensitized to an antigen during the initial exposure. Upon subsequent exposure, these sensitized T cells release cytokines, attracting more immune cells to the site, causing inflammation and tissue damage. Examples of DTH include the positive tuberculin skin test and allergic contact dermatitis, such as reactions to poison ivy.

Contact Dermatitis

Contact dermatitis is a type of skin inflammation that occurs when the skin comes into direct contact with an allergen or irritant. There are two main types of contact dermatitis: irritant contact dermatitis and allergic contact dermatitis.
Allergic contact dermatitis is a classic example of Type IV hypersensitivity. It occurs when T cells react 24-72 hours after exposure to an allergen like poison ivy, nickel, or certain cosmetics. Symptoms may include redness, swelling, and itching at the site of contact. Understanding contact dermatitis is important for diagnosing and managing allergic reactions effectively.