Which of the following immune cells have the expression of CD8 on their faces
**Core Concept**
CD8 is a cell surface glycoprotein that serves as a co-receptor for T-cell receptors (TCRs) on the surface of T cells. It plays a crucial role in the recognition of antigens presented by major histocompatibility complex (MHC) class I molecules.
**Why the Correct Answer is Right**
CD8+ T cells, also known as cytotoxic T cells (CTLs), express CD8 on their surface. They recognize and kill infected cells or tumor cells by binding to MHC class I molecules on the surface of these cells. This interaction between CD8+ T cells and MHC class I molecules triggers a cascade of intracellular signaling events that ultimately lead to the release of cytotoxic granules and the destruction of the target cell. CD8+ T cells are essential for the immune system's ability to eliminate viral infections and cancer cells.
**Why Each Wrong Option is Incorrect**
**Option A:** CD4+ T cells, also known as helper T cells, express CD4 on their surface, not CD8. They play a critical role in coordinating the immune response by activating and directing other immune cells.
**Option B:** B cells, also known as plasma cells, do not express CD8 on their surface. They are responsible for producing antibodies to fight infections and are an essential part of the adaptive immune response.
**Option C:** Natural killer (NK) cells do not express CD8 on their surface. They are a type of lymphocyte that plays a key role in the innate immune response, recognizing and killing infected cells or tumor cells without prior antigen exposure.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that CD8+ T cells are responsible for killing infected cells or tumor cells, whereas CD4+ T cells help to activate and direct other immune cells. This distinction is critical in understanding the different roles of these T cell subsets in the immune response.
**Correct Answer: C. Natural killer (NK) cells do not express CD8 on their surface. They are a type of lymphocyte that plays a key role in the innate immune response, recognizing and killing infected cells or tumor cells without prior antigen exposure.