How does the loss of MHC class I receptors affect the immune system?

The correct answer highlights the critical role of MHC class I molecules in the immune response, particularly concerning the function of cytotoxic T cells (CD8+ T cells). MHC class I receptors are found on nearly all nucleated cells in the body and are essential for presenting endogenous antigens, such as those derived from viral infections or intracellular pathogens, to cytotoxic T cells.

When MHC class I receptors are lost or dysfunctional, cytotoxic T cells cannot effectively recognize and bind to infected or abnormal cells. This impairment severely hampers the immune system's ability to eliminate cells that harbor pathogens, leading to an increased risk of persistent infections and possibly allowing tumor cells to evade immune surveillance. The cytotoxic T cells are specifically designed to kill cells that present abnormal peptides (such as those from viruses), and without MHC class I, they are unable to receive the signal indicating that a cell is infected or diseased.

In contrast, the other options do not accurately reflect the direct consequences of MHC class I loss. B cell activation primarily relies on help from T helper cells and is not directly influenced by MHC class I. Antibody production also requires T cell interactions but is more related to MHC class II molecules, which present exogenous antigens