Complement research tools, everything you want is here!

In addition to Ig molecules in blood or body fluids, another type of macromolecules involved in immune effects are also found, called complement molecules. Its chemical composition is a group of immunoglobulins with enzymatic activity, accounting for about 10% of the total serum globulins. Early immunological studies found that this substance is essential in immune hemolytic reaction and bacteriolytic reaction, so it is called complement. Research in recent years has proved that complement is composed of 11 serum proteins, which are named C1...C9 according to the order of their discovery. Among them, C1 is composed of three subunits: Clq, Clr, and Cls, collectively referred to as the complement system.

The complement system, also known as the complement cascade, is a part of the immune system that enhances the ability of (complement) antibodies and phagocytes to remove microorganisms and damaged cells from the organism, promote inflammation and attack the cell membrane of pathogens. The complement system is composed of many small proteins, which are synthesized by the liver and circulate in the blood as inactive precursors. When stimulated by one of several triggers, the proteases in the system cleave specific proteins to release cytokines and trigger an amplification cascade of further cleavage. Therefore, the complement system is an important effector system and effect amplification system in the body, and its activation process is represented by a series of cascade enzymatic hydrolysis reactions of serine proteases. Three activation pathways of complement:

More specifically, complement triggers the following immune functions:

Complement System Pathways

Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the lectin pathway.

Overview of three pathways of complement system. Fig.1 Overview of three pathways of complement system.

  1. Classical pathway
  2. The classical pathway is triggered by the activation of the C1 complex. The activator (antigen-antibody complex) binds to C1q to activate C1r, C1s, C4, C2, C3 in order to form a cascade enzymatic reaction process of C3 convertase (C4b2a) and C5 convertase (C4b2a3b).

    C5b ~ C9 of the complement system constitute the MAC (membrane attack complex). The membrane attack complex (C5b6789n) is firmly attached to the surface of the target cell, and eventually causes the cell to rupture and die.

  3. Alternative pathway
  4. The difference between the alternative activation pathway and the classical activation pathway is that, the activation of the alternative pathway bypasses the three components of C1, C4 and C2 and directly activates C3. With the participation of factor B, factor D and properdin (P), C3 convertase and C5 convertase are formed, and a cascade of enzymatic reactions is initiated. In addition, the activating substances of the alternative activation pathway are not antigen-antibody complexes but bacterial cell wall components-lipopolysaccharides, as well as polysaccharides, peptidoglycans, teichoic acid, and aggregated IgA and IgG4. The alternative activation pathway can play an important anti-infective effect in the early stage of bacterial infection when no specific antibodies are produced.

    The classical and alternative complement pathways. Fig.2 The classical and alternative complement pathways.

  5. Lectin pathway / Mannose-Binding Lectin (MBL) pathway
  6. The lectin pathway is a cascade reaction in the complement system. Its structure is similar to the classical complement pathway. After activation, it proceeds through the action of C4 and C2, thereby further producing activated complement proteins downstream of the cascade reaction. Contrary to the classical complement pathway, the lectin pathway cannot recognize antibodies that bind to its target. The lectin pathway starts with mannose-binding lectin (MBL) or ficolin (Ficolin-1, Ficolin-2, and Ficolin-3) that bind certain sugars.

    In this pathway, mannose-binding lectins bind to mannose, glucose, or other sugars with 3- and 4-OH groups. After binding to the target molecule, MBL, CL-K1 and ficolins form a complex with MBL-related serine proteases 1 and 2 (MASP-1 and MASP-2), which cleave C4 and C2 to form C3 convertase (C4b2a), the complement cascade is then activated to form a membrane attack complex.

The lectin complement pathway. Fig.3 The lectin complement pathway.

The complement system plays an extremely important role in innate immune regulation, and there are more and more researches on the complement system. As a well-known supplier of products and solutions in the field of life sciences, Creative Biolabs provides you with the world's leading innate immune research reagent. Our complete complement research tools include: proteins/peptides involved in the complement system, ELISA assay kits suitable for a variety of samples, and affinity antibodies of a variety of species.

Complement proteins and peptides: More..

Product Name Species CAT#
Human C5 Protein, Natural - 200 µg Human CB-P271-K
Human C1q Protein, Natural - 1 mg Human CB-P272-K
Cobra Venom Factor Protein, Recombinant - 50 µg CB-P273-K
Human Properdin Protein, Natural - 100 µg Human CB-P274-K
Human Complement factor B Protein, Natural - 250 µg Human CB-P275-K
Human C4 Protein, Natural - 250 µg Human CB-P276-K
Rat C5L2 Protein, Peptide - 10 µg Rat CB-P277-K
Human Complement factor I Protein, Natural - 100 µg Human CB-P278-K
Human Complement factor H Protein, Natural - 250 µg Human CB-P279-K
Human C3a des Arg Protein, Natural - 50 µg Human CB-P280-K
Human C3a Protein, Natural - 50 µg Human CB-P281-K
Human C3 Protein, Natural - 250 µg Human CB-P282-K
Human C2 Protein, Natural - 50 µg Human CB-P283-K
Human C1 Protein, Natural - 200 µg Human CB-P284-K
Human C5L2 Peptide - 10 µg Human CB-P285-K

Complement system component assay kit: More..

Product Name Species CAT#
Complement C4D ELISA Kit [Human] Human CB-P057-K
Alternative Complement Pathway ELISA Kit [Human] Human CB-P058-K
Classical Complement Pathway ELISA Kit [Human] Human CB-P059-K
MBL Complement Pathway ELISA Kit [Human] Human CB-P060-K
Complement System Screen Kit [Human] Human CB-P061-K
Complement TCC/sC5b-9 [Human] Human CB-P062-K
Complement C3 Convertase (C3 Convertase) Detection Kit (Chemiluminescence Immunoassay) Human CB-P063-K
Complement Classical Pathway ELISA [Human] Human CB-P064-K
Complement TCC ELISA Kit [Human] Human CB-P065-K
Classical Complement Pathway Assay Kit [Rat] Rat CB-P066-K
Lectin Complement Pathway Assay Kit [Rat] Rat CB-P067-K
Alternative Complement Pathway Assay Kit [Rat] Rat CB-P068-K
Complement Pathway ELISA Kit, Plus [Rat] Rat CB-P069-K
Complement Factor B ELISA kit [Human]-1 x 96 det. Human CB-P070-K
Complement Factor B ELISA kit [Human]-2 x 96 det. Human CB-P071-K

Complement related antibodies: More..

Product Name Species CAT#
Anti-Human CR2 Monoclonal Antibody (clone BU33) -100 µg Human CB-P138-K
Anti-Human C3b/iC3b/C3c Monoclonal Antibody (clone C3-42.3) -100 µg Human CB-P139-K
Anti-Human iC3b/C3dg/C3d Monoclonal Antibody (clone C3-12.2) -100 µg Human CB-P140-K
Anti-Human C3b/iC3b Monoclonal Antibody (clone 3E7) -100 µg Human CB-P141-K
Anti-Human C3b/iC3b Monoclonal Antibody (clone 5G9) -100 µg Human CB-P142-K
Anti-Human TCC Monoclonal Antibody (clone aE11) -100 µg Human CB-P143-K
Anti-Human CD46 Monoclonal Antibody (clone M177) -100 µg Human CB-P144-K
Anti-Mouse C1q Monoclonal Antibody (clone JL-1) -100 µg Mouse CB-P145-K
Anti-Mouse C5 Monoclonal Antibody (clone BB5.1) -100 µg Mouse CB-P146-K
Anti-Human C1q Monoclonal Antibody (clone JL-1) -100 µg Human CB-P147-K
Anti-Human Factor Ba neoepitope Monoclonal Antibody (clone D22/3) -100 µg Human CB-P148-K
Anti-Pig DAF Monoclonal Antibody (clone PD2) -100 µg Pig CB-P149-K
Anti-Rat CD46 Monoclonal Antibody (clone MM.1) -100 µg Rat CB-P150-K
Anti-Rat CD59 Glycoprotein Monoclonal Antibody (clone TH9) -100 µg Rat CB-P151-K
Anti-Rat DAF Monoclonal Antibody (clone RDII-24) -100 µg Rat CB-P152-K

For more detailed information, please feel free to contact us or directly sent us an inquiry.


Creative Biolabs provides luciferase-based ADCC assay. This Jurkat cell based assay is pioneered by Creative Biolabs, and the methodology is very well accepted by the field. See attached ADCC Reporter Assay Protocol for further details. 

All products and services are for Research Use Only. Do Not use in humans.


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