Question 23

Cytokines are released by one type of immune cell to directly activate another immune cell.

Cytokines are signaling molecules produced by immune cells that play a crucial role in cell communication, especially in the activation and regulation of immune responses.

A) lysozymes

Lysozymes are enzymes that break down bacterial cell walls, contributing to the immune defense but do not function as signaling molecules to activate other immune cells. Therefore, they do not fit the context of directly activating another immune cell.

B) cytokines

Cytokines are indeed the correct answer as they are specifically released by immune cells to facilitate communication and activation of other immune cells. They play a pivotal role in the immune response by promoting inflammation and guiding immune cell function.

C) perforin

Perforin is a protein that forms pores in the membranes of target cells, facilitating cell lysis, particularly in the context of cytotoxic T cells and natural killer cells. It does not activate immune cells; instead, it helps eliminate infected or cancerous cells.

D) granzymes

Granzymes are serine proteases released by cytotoxic T cells and natural killer cells that enter target cells through the pores formed by perforin. While they play a role in apoptosis of target cells, they do not act as signaling molecules to activate other immune cells.

Conclusion

Cytokines are essential for the immune system's communication and activation processes, making them the direct activators among immune cells. Other options, such as lysozymes, perforin, and granzymes, serve different functions within the immune response and do not fulfill the role of activating other immune cells. Thus, cytokines stand out as the correct answer.