Lymphoid System and Cellular Immunology Answers 283target. Helper T cells are greatly diminished during the immunodeficiency
that follows AIDS infection. Natural killer (NK) cells comprise about 10–15%
of circulating lymphocytes. They produce products that kill tumor cells.
Interleukin-1 (IL-1) plays a critical role in inflammation and in the
immune response mediating pathogenetic events. IL-1 is mainly secreted
by monocytes and macrophages and binds to T cells that have been acti-
vated by exposure to antigenic or mitogenic stimuli. Binding of IL-1
induces activated T cells to produce IL-2. There are two forms of IL-1: ker-
atinocytes secrete IL-1αand monocytes/macrophages secrete IL-1β. IL-1
binds to receptors on activated T cells to induce production and release of
IL-2. IL-1 has a wide variety of other effects including induction of
chemokine expression [e.g., monocyte chemoattractant protein-1, (MCP-1)],
upregulation of vascular adhesion molecules (e.g., selectins) by capillary
endothelium, and upregulation of matrix metalloproteases (MMPs) that
degrade the extracellular matrix and degrade IL-1. IL-1 is also required for
IFN-γ production. See the diagram that illustrates the role of IL-1 and IL-2
in communication between immune cells.