Antibody-dependent cell-mediated cytotoxicity (ADCC) is an immune response mechanism in which antibodies bound to antigens on target cells stimulate effector cells, such as natural killer (NK) cells, to destroy those target cells. It represents a collaboration between the humoral and cellular arms of the immune system.
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ADCC is an important defense mechanism against viruses, bacteria, and tumor cells by enhancing the killing of target cells.
The process involves antibodies binding to antigens on the surface of target cells, which then crosslink Fc receptors on effector cells like NK cells.
Crosslinking of Fc receptors activates the effector cell, triggering the release of cytotoxic granules that induce apoptosis in the target cell.
ADCC is particularly effective against pathogens that have evaded other immune mechanisms, such as intracellular bacteria or viruses.
The strength of the ADCC response is influenced by the antibody isotype, Fc receptor expression on effector cells, and the density of target antigens.
Review Questions
Explain the role of antibodies in the ADCC process and how it bridges the humoral and cellular immune responses.
In ADCC, antibodies act as a crucial link between the humoral and cellular immune responses. The antibodies bind to antigens expressed on the surface of target cells, such as virus-infected cells or tumor cells. This binding then crosslinks Fc receptors on effector cells, like natural killer (NK) cells, activating them to release cytotoxic granules that induce apoptosis in the target cell. This collaboration between the antibody-mediated humoral response and the cell-mediated killing by effector cells represents a powerful immune defense mechanism against a variety of pathogens and transformed cells.
Describe the key factors that influence the strength and effectiveness of the ADCC response.
The strength and effectiveness of the ADCC response are influenced by several key factors. The antibody isotype, or class, plays a role, as different isotypes have varying affinities for Fc receptors on effector cells. The expression levels of Fc receptors on the effector cells, such as NK cells, also impact the potency of the ADCC response. Additionally, the density of target antigens on the surface of the pathogen or transformed cell is crucial, as higher antigen density allows for more effective crosslinking of Fc receptors and activation of the effector cells. These factors work together to determine the overall potency of the ADCC-mediated immune defense against threats like viruses, bacteria, and cancer cells.
Analyze the significance of ADCC in the immune response against pathogens that have evaded other immune mechanisms, and explain how it contributes to a comprehensive defense against such threats.
ADCC plays a vital role in the immune response against pathogens that have managed to evade other immune mechanisms, such as intracellular bacteria or viruses. These types of threats can often hide from or resist other immune defenses, but ADCC provides an additional layer of protection. By targeting antibody-coated cells for destruction by effector cells like NK cells, ADCC can eliminate infected or transformed cells that have escaped the reach of other immune responses. This comprehensive defense, involving both humoral and cell-mediated components, is crucial for effectively combating pathogens that have developed strategies to avoid immune detection or clearance. The ADCC mechanism, therefore, significantly enhances the immune system's ability to mount a robust and multi-faceted response against a wide range of threats.
The immune response mediated by antibodies produced by B cells, which circulate in the blood and lymph and neutralize or mark pathogens for destruction.
Cell-Mediated Immunity: The immune response mediated by T cells, which directly attack and destroy infected or cancerous cells.