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Complement Antibodies 

The complement system is a crucial part of the (innate) immune system, consisting of over 30 proteins that work together to help identify and destroy foreign pathogens and fight infections. Dysregulation of the system have been linked to a wide range of diseases such as several types of infections, but also to kidney, autoimmunity and eye diseases, thereby affecting millions of people.

Hycult Biotech offers the largest collection of antibodies targeting the complement system across human, rat, mouse and other species. Learn more about the different pathways and the complement antibodies we offer.

There are three major pathways of complement activation: the classical pathway, the lectin pathway, and the alternative pathway.

Classical Pathway

The complement system is an important component of innate immunity. The physiological functions of the complement system include defending against pathogens invasion, clearance of immune complex and apoptotic debris, and maintaining haemostatic balance. The classical pathway is activated when antibodies-antigen complexes are recognised by C1q. These immune complexes trigger a cascade of complment proteins to bind and activate one another, under normal physiological conditions ultimately leading to the formation of the membrane attack complex (MAC) that punctures and destroys the pathogen’s cell membrane.
C1q, a key player in the classical complement pathway, seamlessly bridges innate and adaptive immunity. As part of the C1 complex, along with C1r and C1s, it activates upon binding to antibody-antigen complexes. This vital function positions C1q as an essential mediator in immune clearance, preventing overstimulation.

Lectin pathway

In the lectin pathway, mannose binding-lectin (MBL) together with MBL-associated serine proteases (MASP) form complexes with polymeric lectin molecules which are involved in pattern recognition. Upon binding of the recognition molecules to carbohydrates on the surface of microorganisms, MASP are converted to their active forms and initiate complement activation. Three types of human MASP have been reported. MASP-1, MASP-2 and MASP-3. The structure of these complexes and subsequent activation is quite similar to the C1-antibody complex from the classical pathway.

When The lectin pathway is activated this leads, via C2b and C4b, to the formation of the C3-convertase. From this point the cascade of protein activation is similar to the classical pathway, ultimately leading to the formation of the MAC complex in the membrane.

Alternative Pathway

The alternative pathway is constantly active at low levels and can be triggered by the presence of certain molecules on the surface of pathogens or damaged host cells. This pathway also leads to t MAC formation. Characteristic for the alternative pathway is the amplification loop via fixed C3bBb and its tight regulation through factor D,I & H.

Terminal Pathway

The three activation pathways converge at the level of C5. C5b is considered the start of the terminal pathway (TP) of complement. After incorporation of C5b into the membrane, the MAC complex is built by subsequent addition of C6, C7, C8 and C9. This is initiated as a result of conformational changes of the preceding complement factor. The MAC complex can be seen as a barrel-shaped structure that inserts itself into the cell membrane, thus creating a pore. Besides its primary function of pathogen elimination, the complement system contributes to numerous auto-immune and inflammatory diseases, like SLE, AMD and transplant rejection. Furthermore, it contributes in the activation of the adaptive immune response.

Basically, the Terminal Complement Complex (TCC) and Membrane Attack Complex (MAC) resemble the same protein complex. The complex can exist as membrane bound variant as well as a soluble variant, respectively in general referred to as MAC and soluble TCC (sTCC; also called sC5b-9).

The emergence of a new generation of complement inhibitors has caused a Renaissance of the complement field. Overall, advancements in structural analysis, diagnostic tools, and understanding of its regulation offer promising avenues for elucidating role of complement in health and disease. Complement proteins and it specific complexes represent a fascinating part in immune biology, holding promise for improved diagnostics and therapeutic interventions in various pathological conditions.

Most popular complement antibodies

C3a/C3a des Arg, Human, mAb 2991

The activation products of the complement cascade, including C3a and C3a des Arg, are key to understanding the complement system’s function.

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C4d, Human, mAb 12D11

The formation of TCC causes lysis of cells or can trigger a variety of cellular metabolic pathways resulting in the synthesis and release of inflammatory mediators.

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C5, Human, mAb 10B6

This specific recognition of this antibody allows it to identify both C3b and full C3, providing valuable insights into the functionality of C3/C3b.

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TCC, Human, mAb aE11

The formation of TCC causes lysis of cells or can trigger a variety of cellular metabolic pathways resulting in the synthesis and release of inflammatory mediators.

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