The recently classified type III interferon

Interferon

Interferons are proteins made and released by host cells in response to the presence of pathogens—such as viruses, bacteria, or parasites—or tumor cells. They allow communication between cells to trigger the protective defenses of the immune system that eradicate pathogens or tumors.IFNs belong to...

 group consists of three IFN-λ (lambda) molecules called IFN-λ1, IFN-λ2 and IFN-λ3 (also called IL29

Interleukin 29

Interleukin-29 is a protein that in humans is encoded by the IL29 gene that resides on chromosome 19.IL-29 is a member of the helical cytokine family and is a type III interferon. It is also known as IFNλ1 and is highly similar in amino acid sequence to the IL-28, the other type III interferon...

, IL28A

Interleukin 28

Interleukin-28 is a cytokine that comes in two isoforms, IL-28A and IL-28B, and plays a role in immune defense against viruses, including the induction an "antiviral state" by turning on Mx proteins, 2',5'-oligoadenylate synthetase as well as ISGF3G...

 and IL28B

Interleukin 28

Interleukin-28 is a cytokine that comes in two isoforms, IL-28A and IL-28B, and plays a role in immune defense against viruses, including the induction an "antiviral state" by turning on Mx proteins, 2',5'-oligoadenylate synthetase as well as ISGF3G...

 respectively). These IFNs signal through a receptor complex consisting of IL10R2 (also called CRF2-4) and IFNLR1 (also called CRF2-12).

Acceptance of this classification is less universal than that of type I and type II, and unlike the other two, it is not currently included in Medical Subject Headings

Medical Subject Headings

Medical Subject Headings is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences; it can also serve as a thesaurus that facilitates searching...

.