Instead, superantigens link the b chain of the TCR directly to the class II MHC molecule on the APC, an interaction that is sufficient to activate the T cell in the absence of any other co-stimulatory signals. Cell-mediated immunity is that in which effector cells play the major role, and antibody plays a minor role or no role at all. Macrophages and neutrophils are important in the elimination of bacteria. Neutrophils kill by producing nitric oxide, while macrophages are a major source of cytokines. Its production is induced by endotoxin.
Macrophages also produce a number of interleukins, interferons and colony-stimulating factors.
IFN a and b are anti-viral and increase MHC class I expression. They produce lytic enzymes, oxygen radicals, major basic protein and eosinophil cationic protein. The activity of eosinophils is enhanced by mast cell and basophil products. NK cells kill by producing perforin, granzymes, and IFN g , and by inducing apoptosis in target cells that express Fas. IFN g has a weak anti-viral effect, synergizes with TNF a to enhance NO synthesis, and increases expression of MHC class I and II molecules.