Kontaktijärjestelmä

Kontaktijärjestelmä, meaning "contact system" in Finnish, refers to a group of plasma proteins that are activated sequentially to initiate and amplify inflammatory responses. These proteins, primarily found in the blood, play a crucial role in the innate immune system, acting as a first line of defense against pathogens. The contact system is distinct from the complement system and the coagulation cascade, although there are interactions between these pathways.

The contact system is primarily triggered by negatively charged surfaces, such as bacterial endotoxins, urate crystals, or damaged tissues. Upon activation, the system involves several key components, including Factor XII (Hageman factor), prekallikrein, high-molecular-weight kininogen (HMWK), and kallikrein. The activation cascade leads to the generation of kallikrein, which cleaves HMWK to release bradykinin. Bradykinin is a potent mediator that causes vasodilation, increased vascular permeability, and pain, all characteristic features of inflammation.

In addition to its role in inflammation, the contact system also contributes to blood coagulation and fibrinolysis. Activated Factor XII can initiate the intrinsic pathway of coagulation. Furthermore, kallikrein can cleave plasminogen to plasmin, an enzyme involved in breaking down blood clots. Dysregulation of the contact system can lead to various clinical conditions, including hereditary angioedema, a disorder characterized by recurrent swelling episodes. Research continues to explore the complex interplay of the contact system and its therapeutic implications.