The biological effects of interferons

Interferons induce a wide range of biological effects. Generally, type I interferons induce similar effects, which are distinct from the effects induced by IFN-y. The most pronounced effect of type I interferons relates to their antiviral activity, as well as their anti-proliferative effect on various cell types, including certain tumour cell types. Anti-tumour effects are likely due not only to a direct anti-proliferative effect on the tumour cells themselves, but also due to the ability of type I interferons to increase NK and T-cytotoxic cell activity. These cells can recognize and destroy cancer cells. 

Not all type I interferons induce exactly the same range of responses, and the antiviral to antiproliferative activity ratio differs from one type I interferon to another. As all bind the same receptor, the molecular basis by which variation in biological activities is achieved is poorly understood as yet. 

IFN-y exhibits, at best, weak antiviral and anti-proliferative activity. When co-administered with type I interferons, however, it potentates these IFN-a/p activities. IFN-y is directly involved in regulating most aspects of the immune and inflammatory responses. It promotes activation, growth and differentiation of a wide variety of cell types involved in these physiological processes (Table 8.7). 

IFN-y represents the main macrophage-activating factor, thus enhancing macrophage-mediated effects, including  

Binding of IFN-y to its surface receptor on polymorphonuclear neutrophils induces increased expression of the gene coding for a neutrophil cell surface protein capable of binding the Fc portion (i.e. the constant region see also Box 13.2) of IgG. This greatly increases the phagocytotic and cytotoxic activities of these cells. 

IFN-y also directly modulates the immune response by alfecting growth, dilferentiation and function of both T and B lymphocytes. These elfects are quite complex, and are often influenced by additional cytokines. IFN-y acts as a growth factor in an autocrine manner for some T cell sub-populations, while it is capable of suppressing growth of other T cell types. It appears to have an inhibitory effect on development of immature B lymphocyte populations but may support mature B cell survival. It can both upregulate and downregulate antibody production under various circumstances. 

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