Which cells secrete chemicals that attack and kill invading microbes?

The correct choice consists of T lymphocytes, specifically a subset known as cytotoxic T cells, which play a crucial role in the immune response against invading microbes. These cells are trained to identify and eliminate infected cells and can recognize antigens presented by these cells. When activated, cytotoxic T cells release perforin and granzymes, which form pores in the target cell's membrane and induce apoptosis, effectively killing the infected cells and helping to clear the infection.

While B lymphocytes are vital for producing antibodies that neutralize pathogens, natural killer cells provide a rapid response to viral-infected cells and tumors, and macrophages are important for phagocytosing and digesting microbes and presenting antigens. However, it is T lymphocytes that directly engage with infected cells and orchestrate a targeted destruction of those cells, highlighting their significant role in cell-mediated immunity.