Some Important Cytokines

■ Interferons (IFNs)are glycoproteins important in the control of viral infections. In addition to being antiviral, IFN-gamma helps regulate the function of cells involved in the inflammatory response, particularly mononuclear phagocytes, and modulates certain responses of adaptive immunity. A number of interferons are available as commercial products in treating disease conditions such as hepatitis and some cancers.

■ Interleukins (ILs)are produced by leukocytes; at least 18 interleukins with various functions have been studied. As a group, interleukins are important in both innate immunity, including the inflammatory response, and in adaptive immunity. Their activities often overlap.

■ Tumor necrosis factors (TNFs)were discovered because of their activities in killing tumor cells, but they actually have multiple roles. TNF-alpha, which is produced by macrophages and other cell types, plays an instrumental role in initiating the inflammatory response. Tumor necrosis factors can also initiate the process of programmed cell death, or apoptosis. Monoclonal antibodies that block the act ion of TNF are an available therapy for some of these conditions.

Figure 1. Blood and Lymphoid CellsAll these types of cells are derived from precursor stem cells found in the bone marrow. Some of the steps not yet clearly defined are indicated by dotted arrows. Multiple steps occur between the stem cell and the final cells produced.

Groups of cytokines often act together to facilitate a particular response by the host defenses. For example, cytokines referred to as pro-inflammatory cytokinescontribute to inflammation (TNF-alpha, IL-1, IL-6, and others). Others are especially involved in promoting antibody responses (IL-4, IL-5, IL-10, and IL-14). A different group promotes responses that involve certain groups of T cells (IL-2, and IFN-gamma, and others).