Killer cells & helper cells are part of –
**Core Concept**
Killer cells and helper cells are types of lymphocytes, which are a subset of white blood cells that play a crucial role in the immune system. Killer cells, also known as cytotoxic T cells, are responsible for directly killing infected cells or tumor cells, while helper cells, also known as T helper cells, assist in activating and directing other immune cells.
**Why the Correct Answer is Right**
Killer cells and helper cells are both types of T cells, which are a subset of lymphocytes. T cells are characterized by the presence of the T cell receptor (TCR) on their surface, which recognizes and binds to specific antigens. Killer cells express the CD8 co-receptor, while helper cells express the CD4 co-receptor. Both types of cells play essential roles in cell-mediated immunity, with killer cells directly killing infected cells and helper cells assisting in activating and directing other immune cells.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because killer cells and helper cells are not types of B cells, which are another subset of lymphocytes that produce antibodies to neutralize pathogens.
**Option B:** This option is incorrect because killer cells and helper cells are not types of macrophages, which are a type of phagocytic cell that engulfs and digests foreign particles and microorganisms.
**Option C:** This option is incorrect because killer cells and helper cells are not types of dendritic cells, which are a type of antigen-presenting cell that helps to activate T cells.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that killer cells and helper cells are both types of T cells, and understanding their distinct roles in cell-mediated immunity is crucial for diagnosing and treating various immune-related disorders.
**Correct Answer:** D. T cells