Interleukin-1 and lipopolysaccharide enhance intercellular adhesion molecule-1 expression in cell lines of human squamous cell carcinoma

Changing paradigms in dermatology: tumor necrosis factor alpha (TNF-alpha) blockade in psoriasis and psoriatic arthritis

Psoriasis is an inflammatory T cell-mediated disease characterized by epidermal hyperplasia and parakeratosis, resulting in lesional areas of thick and scaling skin. Elevated levels of proinflammatory cytokines, including TNF-alpha, are found in psoriatic lesions. TNF-alpha has many effects in producing an inflammatory response such as stimulating production of pro-inflammatory molecules (eg, IL-1, IL-6, IL-8, NF-kappaB) and adhesion molecules (eg, ICAM-1, P-selectin, E-selectin). As such, TNF-alpha is a target for immunotherapy in the treatment of psoriasis and psoriatic arthritis. The role of TNF-alpha in the pathogenesis of psoriasis is reviewed, along with clinical trials demonstrating the efficacy of new anti-TNF-alpha immunobiologics in the treatment of psoriasis and psoriatic arthritis.

Proinflammatory cytokines upregulate expression of calprotectin (L1 protein, MRP-8/MRP-14) in cultured human keratinocytes

BACKGROUND

Normal skin contains no epidermal calprotectin. In biopsies from various inflammatory skin disorders, however, this antimicrobial protein occurs in the cytoplasm of keratinocytes.

OBJECTIVES

To exclude the possibility of epidermal uptake of calprotectin from granulocytes and macrophages in diseased skin, we investigated whether cytokine-stimulated human keratinocytes can express calprotectin in vitro.

METHODS

Keratinocytes from healthy individuals were cultured in serum-free keratinocyte medium. The cells were stimulated with different cytokines [interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-10 and IL-13], both separately and in various combinations. Cytoplasmic protein levels of calprotectin were measured by an enzyme-linked immunosorbent assay performed on fixed adherent keratinocytes, and mRNA expression was determined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Calprotectin was produced by cytokine-stimulated keratinocytes, especially in response to combinations of the proinflammatory cytokines, which showed an additive upregulatory effect. When expression of mRNA for the light (MRP-8) and heavy (MRP-14) calprotectin chain was determined by RT-PCR, their respective levels were shown to be increased four- to ninefold and three- to fivefold after 24 h of combined stimulation with IFN-gamma and TNF-alpha. The time course of calprotectin production showed no significant elevation for the first 16 h but then increased and peaked after 36 h.

CONCLUSIONS

Cultured human keratinocytes stimulated with proinflammatory cytokines produce calprotectin, suggesting that epidermal expression of this antimicrobial protein in diseased skin reflects compartmentalized synthesis rather than uptake from dermal inflammatory cells.

Keratins and the keratinocyte activation cycle

In wound healing and many pathologic conditions, keratinocytes become activated: they turn into migratory, hyperproliferative cells that produce and secrete extracellular matrix components and signaling polypeptides. At the same time, their cytoskeleton is also altered by the production of specific keratin proteins. These changes are orchestrated by growth factors, chemokines, and cytokines produced by keratinocytes and other cutaneous cell types. The responding intracellular signaling pathways activate transcription factors that regulate expression of keratin genes. Analysis of these processes led us to propose the existence of a keratinocyte activation cycle, in which the cells first become activated by the release of IL-1. Subsequently, they maintain the activated state by autocrine production of proinflammatory and proliferative signals. Keratins K6 and K16 are markers of the active state. Signals from the lymphocytes, in the form of Interferon-gamma, induce the expression of K17 and make keratinocytes contractile. This enables the keratinocytes to shrink the provisional fibronectin-rich basement membrane. Signals from the fibroblasts, in the form of TGF-beta, induce the expression of K5 and K14, revert the keratinocytes to the healthy basal phenotype, and thus complete the activation cycle.