IL-20: biological functions and clinical implications.

IL-20 belongs to the IL-10 family and plays a role in skin inflammation and the development of hematopoietic cells. Little is known about its other biological functions and clinical implications, however. Updated information about IL-20, such as its identification, expression, receptors, signaling, biological activities, and potential clinical implications, is illustrated in this review based on our research and on data available in the literature. Our studies of IL-20 show that it is a pleiotropic cytokine with potent inflammatory, angiogenic, and chemoattractive characteristics. Inflammation and angiogenesis are essential for the pathogenesis of rheumatoid arthritis and atherosclerosis. Based on in vitro data and clinical samples, we demonstrated that IL-20 is involved in the diseases of rheumatoid arthritis and atherosclerosis. In addition, we found in our studies that IL-20 signaled through different molecules in several cells. The present review presents the clinical implications of IL-20 in rheumatoid arthritis and atherosclerosis. It may provide new therapeutic options in the future.

Detection of IL-20 and its receptors on psoriatic skin.

The aim of this study was to investigate the expression of interleukin-20 (IL-20) and its receptors on psoriatic skin by immunohistochemical analysis and to evaluate the correlation of CD8-positive T lymphocytes with epidermal proliferation. Overexpression of IL-20 and its receptors was detected in the keratinocytes of the lesional skin of psoriasis and spongiotic dermatitis. The expression pattern of IL-20 spreads throughout the whole layer of epidermis, while IL-19 was expressed in up to three or four layers suprabasally. The serum level of IL-20 in psoriatic patients was significantly lower than that in healthy controls. IL-20 upregulated KGF transcripts on CD8-positive T cells. We hypothesize that overexpression of IL-20 is correlated with keratinocyte proliferation that acts through their receptor complex expressed by keratinocytes themselves. Furthermore, IL-20 can stimulate CD8-positive lymphocytes to produce KGF, which may contribute to sustaining the hyperproliferative status of the keratinocytes.

IL-19 induced Th2 cytokines and was up-regulated in asthma patients.

IL-19 belongs to the IL-10 family, which includes IL-10, IL-19, IL-20, IL-22, melanoma differentiation-associated gene-7 (IL-24), and AK155 (IL-26). IL-10 has been shown to inhibit allergen-induced airway hyperreactivity and inflammation. To determine whether IL-19 was also associated with asthma, we used ELISA to analyze the serum level of IL-19 in patients with asthma and found that their serum IL-19 levels were twice those of healthy controls. Patients with a high level of IL-19 also had high levels of IL-4 and IL-13. In a dust mite-induced murine model of asthma, we found that IL-19 level in asthmatic BALB/cJ mice was also twice that of healthy control mice. IL-19 transcript was also induced in the lungs of asthmatic mice. Electroporation i.m. of the IL-19 gene into healthy mice up-regulated IL-4 and IL-5, but not IL-13. However, IL-19 up-regulated IL-13 in asthmatic mice. In vitro, IL-19 induced IL-4, IL-5, IL-10, and IL-13 production by activated T cells. Activation of T cells was required for induction of IL-13 because IL-19 did not induce IL-13 production on nonstimulated T cells. Taken together, these results demonstrated that IL-19 up-regulates Th2 cytokines on activated T cells and might play an important role in the pathogenesis of asthma.