Page 79 - Veterinary Immunology, 10th Edition

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FIG. 3.2 The origins and some of the biological activities of
interleukin-1.

During severe infections, IL-1β circulates in the bloodstream

where, in association with TNF-α, it is responsible for sickness
behavior. Thus it acts on the brain to cause fever, lethargy, and
malaise. It acts on muscle cells to mobilize amino acids, causing
pain and fatigue. It acts on liver cells to induce the production of

new proteins, called acute-phase proteins, that also assist in the
defense of the body (Chapter 7).
The most important IL-1 receptors are CD121a and CD121b.
CD121a is a signaling receptor, whereas CD121b is not. CD121b

thus binds IL-1, but nothing more happens. If soluble CD121b binds
IL-1, it acts as an antagonist. IL-1 activity is also regulated by IL-1
receptor antagonist (IL-1RA), a protein that binds and blocks
CD121a. IL-1RA is therefore an important regulator of IL-1 activity

and inflammation. It reduces mortality in septic shock and graft-
versus-host disease and has antiinflammatory effects (Chapter 8).
IL-1 is a member of a large family of cytokines that regulate
innate immune responses. Other important family members include
IL-1RA, IL-18, IL-33, IL-36, IL-37, and IL-38 (Chapter 8 and

Appendix 3). All these cytokines signal through closely related
receptors. Some, like IL-36, have a proinflammatory effect, while
others such as IL-37 have antiinflammatory effects.

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