Question 1

What is the Meaning of Type IV Hypersensitivity?

Accepted Answer

Type IV Hypersensitivity is a delayed-type, cell-mediated immune reaction, distinct from antibody-mediated responses. It primarily involves T lymphocytes and macrophages. Clinical manifestations typically develop 24 to 72 hours after antigen exposure, defining its characteristic delayed onset within immune reactions.

Question 2

What is the Context of Type IV Hypersensitivity?

Accepted Answer

Within the adaptive immune system, Type IV Hypersensitivity acts as a critical defense against intracellular pathogens and specific environmental antigens. This response activates T helper cells and cytotoxic T lymphocytes after antigen-presenting cells process antigens. It also contributes to immune surveillance and mediates tissue rejection.

Question 3

What is the Significance of Type IV Hypersensitivity?

Accepted Answer

Understanding Type IV Hypersensitivity is clinically important, explaining the pathology of many conditions and diagnostic tests. It accounts for delayed skin reactions in contact dermatitis, like from nickel. This mechanism is central to the tuberculin skin test for tuberculosis exposure and contributes to certain autoimmune disorders.

Question 4

What is the Mechanism of Type IV Hypersensitivity?

Accepted Answer

The mechanism involves sensitization and effector phases. During sensitization, antigen-presenting cells activate naive T cells into specific T helper (Th1) or cytotoxic T lymphocytes. Upon re-exposure, these activated T cells release cytokines, recruiting and activating macrophages. This leads to localized inflammation and tissue damage.

Question 5

What is the Application of Type IV Hypersensitivity?

Accepted Answer

Clinically, Type IV Hypersensitivity applies to diagnostic and therapeutic areas. Patch testing identifies contact allergens by eliciting a delayed skin reaction. The PPD skin test for tuberculosis screening directly relies on this immune response. This understanding is vital for managing chronic inflammatory conditions and preventing organ rejection.

Question 6

What is the Metric of Type IV Hypersensitivity?

Accepted Answer

Assessment involves clinical observation and specific diagnostic tests. For skin reactions, erythema and induration size are measured 24 to 72 hours post-exposure. Tissue biopsies may reveal perivascular lymphocytic infiltration. In vitro assays, like lymphocyte proliferation tests, can quantify T-cell responses to specific antigens.

Question 7

What is the Risk of Type IV Hypersensitivity?

Accepted Answer

While protective, an exaggerated or misdirected Type IV response carries significant clinical risks. Severe contact dermatitis can lead to extensive skin damage and secondary infections. In autoimmune diseases, an inappropriate Type IV response causes chronic inflammation and tissue destruction. This immune reaction is also a primary driver of chronic organ transplant rejection.

Type IV Hypersensitivity

Meaning

Context

Significance

Mechanism

Application

Metric

Risk

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