IL-32 is the name given to the NK4 transcript first reported in
IL-2 activated T lymphocytes and natural killer cells 13 years ago without known function. The novel
cytokine has six
isoforms. In an study to isolate a soluble form of the IL-32 receptor from human urine, IL-32alpha bound proteinase-3 with high affinity and was not affected by
enzyme inhibition. IL-32alpha/IL-32gamma were expressed as recombinant molecules. The
cytokine exhibits properties characteristic of proinflammatory
cytokines and also induces the degradation of inhibitory kappaB and phosphorylation of
mitogen activated
protein p38.
Monoclonal antibodies to IL-32 identify its presence in a variety of human tissues from diseases states. Epithelial cells from healthy subjects express low levels of the
cytokine, but in disease conditions such as
chronic obstructive pulmonary disease,
Crohn's disease and
psoriasis, the expression increases markedly. IL-32 is a major transcript in gene array studies in epithelial cells stimulated with IFNgamma in vitro. In
rheumatoid arthritis, synovial tissues reveals increased content of IL-32, which correlates with severity of disease. A highly significant correlation has been observed between the number of synovial and macrophagic cells positive for IL-32 and the level of erythrocytes sedimentation, IL-1beta, tumour
necrosis factor alpha, and
IL-18. Thus, IL-32 exhibits many properties of proinflammatory
cytokines and associations with disease severity.