[Cystatin C--modulator of immune processes]

Cystatin C is a lowmolecular protein (13 kDa) that inhibits the activity of lysosomal cysteine proteinases with the strongest activity against cathepsin B and H. The recent experiments show that the level of cystatin C is independented of chronic and acute inflammatory process which frequently coexist with end stage renal diseases. Recent studies challange the theory because a higher concentration of cystatin C in serum correlated well with a higher concentration of inflammatory markers such as a CRP and fibrinogen in the patients. In vitro experiments on cultured monocytes and macrophages discovered that after stimulation by LPS and INF the expression of the cystatin C gene and synthesis of this protein was reduced. Cystatin C plays important modulatory function in regulation of the natural immunity, protecting our body against viruses, bacteries and parasites. Moreover, cystatin C binds the C4 component and modulates activation of the classical complement pathway. The experiments also show that cystatin C could influence non-specific immune response through the inhibition of the superoxide anion generation (respiratory burst), phagocytosis, chemotaxis and apoptosis of neutrophils. Similarly, the cystatin C can modulate the specific immune response through the inhibition of cathepsin S, bindining membrane receptors for TGF-beta or increasing MHC class II expression on dendritic cells.