Final answer:
The correct answer is c. IL-12 secreted by macrophages and IFN-γ produced by NK cells, which is a positive-feedback loop enhancing immune response. Option b.
Step-by-step explanation:
The positive-feedback loop established between macrophages and dendritic cells in infected tissues involves the secretion of IL-12 by the macrophage and IFN-γ (interferon-gamma) by the Natural Killer (NK) cell. Macrophages play a crucial role in the innate immune response and are involved in phagocytosis of pathogens. When an infection occurs, macrophages can stimulate naive T cells to become TH1 cells, which then produce cytokines that improve the macrophage's capability to destroy intracellular pathogens. Similarly, IL-12 secreted by macrophages acts as a signal to potentiate NK cells, prompting them to release IFN-γ, a critical cytokine for the immune response, which further activates macrophages and enhances their ability to kill infected or tumor cells.
Thus, the correct answer to the question is c. IL-12; IFN-γ. This interaction enhances both the adaptive and innate immune responses, leading to an effective clearance of the pathogen or infected cells.