Most cytokines are secreted proteins with wide-ranging immunoregulatory and hematopoietic activities as illustrated in Figure 13-4 (in cache) . One cytokine featured at this web site is lymphotoxin-a (LT-a) or tumor necrosis factor-b (TNF-b) as it is sometimes called. This cytokine represents one of several members of the TNF family of cytokines which bind to one or more receptors of the TNF receptor family. Because TNF-like cytokines are homotrimeric in structure, they can bind one, two, or three TNF-like receptors. Receptor clustering appears to be a key initiating step for cytokine function. The three-dimensional structure of the LT-a/(TNF-R1)₃ complex is examined on the linked web page.

The following web sites have additional interesting and useful information regarding cytokine and cytokine receptor structure and function: