Tuberculin Type Hypersensitivities, also known as Type IV delayed hypersensitivity reactions or cell-mediated hypersensitivity, refer to a group of immune responses that occur in the body upon exposure to certain antigens. These antigens are typically derived from mycobacteria, specifically the bacterium Mycobacterium tuberculosis, which is responsible for causing tuberculosis.
In this type of immune response, the body's immune system reacts to the antigen by initiating a complex cascade of events. First, special immune cells called T lymphocytes recognize the antigen and become activated. These activated T cells release chemical mediators, such as cytokines and chemokines, which recruit and activate other immune cells, including macrophages and neutrophils.
The activated macrophages play a critical role in the immune response, as they engulf and destroy the antigen, presenting its fragments on their cell surface to further stimulate the immune system. This process results in the formation of characteristic skin reactions, such as erythema (redness), induration (hardening), and swelling, at the site of antigen exposure.
Tuberculin Type Hypersensitivities are commonly used in diagnostic tests, such as the tuberculin skin test, also known as the Mantoux test or the purified protein derivative (PPD) test, to detect previous exposure to the tuberculosis bacterium. A positive reaction to the test indicates a previous or current infection with Mycobacterium tuberculosis.
It is important to note that while Type IV hypersensitivity responses are associated with protective immunity against tuberculosis, they can also contribute to the development of chronic inflammation and tissue damage in certain situations, such as in individuals with a compromised immune system or in the context of autoimmune diseases.
