Cells that can directly attack target cells include all of the following except a. macrophages, b. cytotoxic T cells, c. helper T cells, d. natural killer cells.

Verified step by step guidance

1. Understand the role of each cell type in the immune response.
2. Macrophages are phagocytic cells that engulf and digest pathogens, but they do not directly attack target cells.
3. Cytotoxic T cells (CD8+ T cells) directly attack and destroy infected or cancerous cells.
4. Helper T cells (CD4+ T cells) assist other cells in the immune response but do not directly attack target cells.
5. Natural killer (NK) cells are part of the innate immune system and can directly attack and kill virus-infected cells or tumor cells.

Key Concepts

Cytotoxic T Cells

Cytotoxic T cells, also known as CD8+ T cells, are a type of immune cell that directly kill infected or cancerous cells. They recognize specific antigens presented by infected cells and release cytotoxic substances that induce apoptosis, or programmed cell death, in the target cells.

Helper T Cells

Helper T cells, or CD4+ T cells, play a crucial role in the immune response by assisting other immune cells rather than directly attacking pathogens. They secrete cytokines that enhance the activity of B cells and cytotoxic T cells, thereby coordinating the overall immune response.

Natural Killer Cells

Natural killer (NK) cells are a type of lymphocyte that can directly attack and destroy virus-infected cells and tumor cells without prior sensitization. They recognize stressed cells in the absence of antibodies and MHC, allowing for a rapid immune response to infected or malignant cells.