Extracellular methods of Killing.

http://en.wikipedia.org/wiki/Phagocyte

Interferon-gamma—which was once called macrophage activating factor—stimulates macrophages to produce nitric oxide. The source of interferon-gamma can be CD4+ T cells, CD8+ T cells, natural killer cells, B cells, natural killer T cells, monocytes, macrophages, or dendritic cells.Nitric oxide is then released from the macrophage and, because of its toxicity, kills microbes near the macrophage.Activated macrophages produce and secrete tumor necrosis factor. This cytokine—a class of signaling molecule—kills cancer cells and cells infected by viruses, and helps to activate the other cells of the immune system.

In some diseases, e.g., the rare chronic granulomatous disease, the efficiency of phagocytes is impaired, and recurrent bacterial infections are a problem.In this disease there is an abnormality affecting different elements of oxygen-dependent killing. Other rare congenital abnormalities, such as Chediak-Higashi syndrome, are also associated with defective killing of ingested microbes.