Final answer:
Cytokines are the broad-ranging molecules secreted by activated T lymphocytes, including helper T cells, which stimulate B cells to become antibody-producing plasma cells and enhance the immune response.
Step-by-step explanation:
The substance secreted by activated T lymphocytes with a broader range of effects than other interferons is known as cytokines. These cytokines include various proteins, among which are interferons, that serve as important signaling molecules in the immune response. Helper T cells (Th cells), particularly, are instrumental for their role in secreting cytokines that enhance various immune responses.
Helper T cells can be classified into different types based on the cytokines they produce. Upon activation, these T cells help stimulate B cells to proliferate and mature into plasma cells capable of producing antibodies. The cytokines secreted by Th cells also contribute to enhancing the cytotoxic function of other T cells and mobilize the innate immune system's components, such as natural killer (NK) cells.
Overall, the role of cytokines secreted by T cells is critical for the functioning of the adaptive immune system, enabling a highly specific and efficient response to pathogens.