Complement component 1s

Complement Component 1

Diagram of the classical pathway of complement activation, showing the role of Complement Component 1.

Complement Component 1 (C1) is a crucial protein complex in the complement system, which is part of the innate immune system. The complement system enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promotes inflammation, and attacks the pathogen's cell membrane.

Structure

C1 is a complex of three different proteins: C1q, C1r, and C1s. These proteins are organized in a specific structure that allows C1 to function effectively in the immune response.

• C1q is a large molecule composed of 18 polypeptide chains, forming a structure that can bind to the Fc region of immunoglobulins.
• C1r and C1s are serine proteases that are activated in a cascade manner.

Function

C1 is the first component of the classical pathway of complement activation. It is responsible for recognizing and binding to the antigen-antibody complex. Upon binding, C1 undergoes a conformational change that activates C1r, which in turn activates C1s. Activated C1s then cleaves and activates the next components in the cascade, C4 and C2, leading to the formation of the C3 convertase.

Activation

The activation of C1 is tightly regulated to prevent excessive inflammation and tissue damage. C1 is activated when C1q binds to the Fc region of IgG or IgM antibodies that are bound to antigens. This binding triggers the activation of C1r and C1s, initiating the complement cascade.

Role in Disease

Deficiencies or dysfunctions in C1 can lead to immune system disorders. For example, C1 deficiency can result in increased susceptibility to infections and autoimmune diseases such as systemic lupus erythematosus.

Related Pages

• Complement system
• Classical pathway
• Antibody
• Immune system