Interferons are a group of signalling proteins (cytokines) that form an integral part of the innate immune system. In the broadest sense, the role of interferons is to facilitate, modulate and mediate the actions and reactions of the immune system by providing inter-cellular communication. The modulating role of interferons in the immune system has up- as well as down-regulating strands.

The clearest example of the role of interferons is, for example, the response to infection of a cell by a virus . A virus-infected cell secretes interferons as an alert and warning message to nearby cells to activate their defence against viral infection. In addition, some interferons activate those cells in the immune system that are responsible for eradicating pathogens, such as macrophages, natural killer cells and T cells. In addition, interferons also have important activating roles in the increased production of some major antigens (MHC antigens) when generally up-regulating a host’s defence against a pathogen.

The role of interferons is not restricted to their support to the immune system in eradicating viral infections. Some interferons are also known to support the immune system in recognising and eliminating malignant cells. The immune-system mechanisms activated in this situation are similar to those at work when the immune system has to deal with viral infections.

Unfortunately, virus strands and malignant cell lines have something else in common. Alongside the evolution of the host’s immune system, getting better at its multiple tasks, also virus strands and malignant cell lines evolve and develop strategies to escape detection and/or eradication by the immune system. These mechanisms include blocking of the signalling role of interferons, or the blocking of the actions triggered by a particular interferon. Some researchers have referred to this co-evolution of host and pathogen as an open-ended arms race. Virus species with abilities to escape the detection and/or action of the human immune system include the Epstein-Barr virus, several species of the herpes virus group (human cytomegalovirus, Kaposi sarcoma-associated herpes virus), the human papilloma virus, HPV which is associated with oropharyngeal malignancies and some strands of influenza virus.

Synthetic (produced by biochemical methods) interferons are used to treat a number of conditions, including multiple sclerosis (interferon beta) and hepatitis C, a viral infection of the liver that is known to be associated with an increased risk to develop liver carcinoma. Combined use of anti-viral drugs and interferon alpha has a high rate of success in treating hepatitis C and leads to reduced risk of malignancy developing on the back of the viral liver infection. A number of different haematological malignancies have been successfully treated with combination therapies including interferon alpha. These conditions include various forms of leukaemia and Hodgkin lymphoma. Treatment with interferon alpha for recurrent melanoma has also been reported. A limiting aspect for the use of interferons as drugs rests in severe adverse effects from systemic use of these agents; this aspect is perhaps not too surprising giving the multiple and varied roles of interferons in the immune system.