Interferons

Interferons: Interferon comprises a group of proteins produced by virus-infected cells.

Did you know? Interferons were originally called this because of their ability to interfere with viral replication in previously uninfected tissue culture cells.

Interferon A and interferon B:

·        Interferon A and interferon B are also known as type I antiviral interferons.

·        It is presumed that double stranded RNA (dsRNA) produced during the viral life cycle can induce the expression of IFN-A and IFN-ß by the infected cell.

·        IFN-A and IFN-ß bind to their respective receptors and act in an autocrine and paracrine fashion to induce an antiviral response or resistance to viral replication.

·        They lead to the transcription of several genes, gene encoding for an enzyme which causes:

1.     Activation of ribonuclease L (RNAse L), which degrades viral RNA.

2.     Induction of a specific protein kinase, which inactivates protein synthesis, thus blocking viral replication in infected cells.

3.     The binding of IFN-A and IFN-ß to NK cells induces lytic activity, making them very effective in killing virally infected cells.

Interferon Y:

·        IFN-Y is distinct functionally from the type I antiviral interferons, IFN-A and IFN-ß, and it is not directly induced by viral infection.

·        It is a cytokine produced by cytotoxic T cells, Th1 cells, and NK cells.

·        IFN-Y inhibits viral replication directly.

·        It induces the increased expression of MHC class I in infected cells. This ensures that infected cells will be recognized for cytotoxic attack.

·        It activates macrophages, recruiting them to sites of infection. Macrophages act as APCs or effector cells.

·        In early response, IFN-Y secreted by NK cells induces activated CD4 T cells to differentiate into Th1 cells, which are able to activate macrophages.

Table 5.2: Interferons and their actions

Cytokine	Secreted by	Action
Interferon A	Leukocytes, dendritic cells	Activates cellular genes, resulting in the production of proteins that confer an antiviral state on the cell; increased MHC class I expression.
Interferon B	Fibroblasts
Interferon Y	Th1 cells, NK cells, CD8+ T cells	Macrophage activation, increased expression of MHC molecules and antigen processing components, Ig class switching, suppresses Th2.

Table 5.3: Therapeutic uses of interferons

Interferon	Clinical use
Interferon A	Hepatitis B Hepatitis C Kaposi sarcoma Melanoma
Interferon B	Multiple sclerosis
Interferon Y	Chronic granulomatous disease (CGD) Osteopetrosis

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