Question

Which innate immune system component uses MHC class I molecules directly in its defense strategy? a. macrophages b. neutrophils c. NK cells d. interferon

Short answer

a. Macrophages b. Neutrophils c. NK cells d. Interferon Answer: c. NK cells

Step-by-step solution

Understanding MHC class I molecules

MHC class I molecules (Major Histocompatibility Complex class I) are proteins present on the surface of all nucleated cells in the body. They play a vital role in the immune system by presenting foreign antigens (such as peptides derived from intracellular pathogens) to cytotoxic T cells, which help to recognize and destroy the infected cells.

Understanding the role of macrophages

Macrophages are a part of the innate immune system and function as professional phagocytes, engulfing and destroying pathogens. Although they can present antigens to T-cells, their primary role in defense is not directly using MHC class I molecules.

Understanding the role of neutrophils

Neutrophils, similar to macrophages, are a part of the innate immune system and function as phagocytes by engulfing and destroying pathogens. Neutrophils do not directly use MHC class I molecules in their defense strategy.

Understanding the role of NK cells

NK cells (Natural Killer cells) are a part of the innate immune system and play a crucial role in immune surveillance. They recognize and destroy virus-infected cells and tumor cells by detecting the downregulation or absence of MHC class I molecules on their surface. NK cells indeed directly use MHC class I molecules to detect abnormal cells and initiate their defense strategy.

Understanding the role of interferon

Interferons are proteins released by cells in response to a viral infection. They alert nearby cells and stimulate them to produce antiviral proteins that inhibit the replication of viruses. Interferon itself does not directly use MHC class I molecules, but it can influence the expression of these molecules on the surface of infected cells.

Identifying the correct answer

Considering the roles of each component in the innate immune system, it is evident that NK cells (option c) are the ones that directly use MHC class I molecules in their defense strategy. Therefore, the correct answer is c. NK cells.