Innate immunity degradation

Terao Y, Mori Y, Yamaguchi M et al. Group A streptococcal cysteine protease degrades C3 (C3b) and contributes to evasion of innate immunity. J Biol Chem 2008 283(10) 6253-6260. 

Predicted activation of the innate immune system during degradation... 

The overview of innate immune system activation on material surfaces (see Section 4.6) assumes that the inherent properties of the material remain constant over time and that the response is mainly due to the protein adsorption onto the material surface. However, the situation is more challenging when it comes to biodegradable materials, because they (obviously) will change in surface topography and size over time. In addition, because the degradation of most commonly used materials leads to the production of hydroxyl acids and eventually carbon dioxide, a lowering of the pH in the adjacent tissue is found. This change in pH leads to a dramatic increase in complement activation and opsonization [4], and to increased inflammation. 

The biocompatibility of a biomaterial is primarily related to its interaction with the innate immune system, ie, ultimately the inflammatory response that is induced. Factors that influence such response include physicochemical and stmctural properties of the surface and the total surface area of the material. For a biodegradable material, these properties change over time and for most polymers, the pH also decreases in the tissue adjacent to the material during degradation. Consequently, the biocompatibility of a biomaterial needs to be reassessed at different steps, because a degrading material no longer possesses the properties of the original, biocompatible material. 

Many bacteria express a variety of peptidases with a different degree of specificity ranging from nonspecific to specific enzymes. Some of them degraded proteins involved in human innate immunity (for review, see Potempa and Pike 2009). An example is the metallopeptidase aureolysin from Staphylococcus aureus that cleaves and inactivates LL-37 (Sieprawska-Lupa et al. 2004). 

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