Which of the following macrophage-secreted cytokines is NOT considered to be stimulators of NK cells? a. \(\mathrm{IL}-1\) b. IL-10 c. IL-12 d. IL-15 e. IL-18 f. IL-2

Natural Killer (NK) cells are a type of white blood cell that play a crucial role in the immune system. They are called natural killers because they can kill infected cells or cancer cells without being activated by specific antigens. These cells are part of the innate immune system, which provides rapid but non-specific responses to pathogens.

Cytokines are small proteins secreted by cells of the immune system, such as macrophages, to regulate immune responses. They can act as signaling molecules to coordinate various cells and promote or inhibit cellular responses. In the context of NK cells, some cytokines can stimulate their differentiation, activation, or proliferation, which might be essential for effective immunity against pathogens.

Now, let's evaluate each cytokine given in the exercise to determine whether they are stimulators of NK cells or not. a. \(\mathrm{IL}-1\): Interleukin-1 (IL-1) is a pro-inflammatory cytokine that plays a role in regulating immune responses. Although it has various functions, it is not considered a significant stimulator of NK cells. b. IL-10: Interleukin-10 (IL-10) is an anti-inflammatory cytokine. IL-10 is known to suppress the production of pro-inflammatory cytokines and inhibit the activation of immune cells, including NK cells. Therefore, IL-10 is NOT a stimulator of NK cells. c. IL-12: Interleukin-12 (IL-12) is a cytokine that promotes the differentiation and activation of NK cells and T cells. It is considered a key stimulator of NK cells. d. IL-15: Interleukin-15 (IL-15) is a cytokine that plays a role in stimulating the proliferation and activation of NK cells. It is considered a significant stimulator of NK cells. e. IL-18: Interleukin-18 (IL-18) is a pro-inflammatory cytokine that enhances the production of interferon-gamma (IFN-γ) by NK cells and T cells. It is also considered a stimulator of NK cells. f. IL-2: Interleukin-2 (IL-2) is a cytokine that promotes the proliferation, differentiation, and activation of various immune cells, including NK cells. It is considered a potent stimulator of NK cells.

Based on our evaluation of each option, we find that IL-10 is the only cytokine listed that does not stimulate NK cells. Therefore, the correct answer is option (b) IL-10.