Question

Some cells may not have class I MHC proteins on their surfaces due to a viral infection or because they have become cancerous. How does the immune system respond?

A. B cells present multiple antigens to a helper T cell for activation.
B. Natural Killer cells attach to these cells and kill them.
C. IgE binds to the cells.
D. Eosinophils engulf them.

Answer 1

When cells lack class I MHC proteins due to viral infection or becoming cancerous, the immune system responds by using Natural Killer cells to kill these cells and activating cytotoxic T cells.

Step-by-step explanation:

When cells are infected by a virus or become cancerous, they may not have class I MHC proteins on their surfaces. In response to this, the immune system has multiple mechanisms to target these cells.

• Natural Killer cells recognize cells that do not have class I MHC proteins and kill them. This is because class I MHC proteins are normally present on healthy cells, so their absence indicates an abnormal or infected cell.
• Cytotoxic T cells are activated by professional antigen-presenting cells, such as dendritic cells, macrophages, and B cells, which present antigens to them. These activated cytotoxic T cells can then directly kill the infected or cancerous cells.
• Eosinophils, which are a type of white blood cell, are mainly involved in the immune response against parasites and may play a role in certain infections. However, they are not specifically activated in response to cells lacking class I MHC proteins.