Complement System
The complement system is part of the innate immune system and plays an important role in the host defense, inflammation, tissue regeneration and other physiological processes. Complement activation results in opsonization of pathogens and their removal by phagocytes. It also causes chemotactic attraction of phagocytes and macrophages. Furthermore, the complement system forms the terminal attack complex (MAC), a membrane channel causing osmotic lysis of the respective pathogen. While complement is not adaptable it does complement the adaptive immune system and it is also involved in B and T cell response regulation.
Activation of complement unfolds along three different complement activation pathways depending on the nature of the pathogen: the classical pathway, the lectin pathway, and the alternative pathway. All three converge into the common terminal pathway that leads to the formation of the MAC. In addition, anaphylatoxins C3a and C5a elicit a plethora of physiological responses that range from chemoattraction to apoptosis. The complement system consists of more than 30 proteins that are either present as soluble proteins in the blood or as membrane-associated proteins. Most exist as inactive zymogens that are then sequentially cleaved and activated. The central component in all three pathways is component C3, the most abundant complement protein found in the blood. Its activation induces the formation of the activation products C3a, C3b, and C5a and ultimately the MAC.
In addition to these three established pathways, it has been shown that factors such as kallikrein, plasmin, thrombin, and factor XIIa activate the complement system independently of the C3 protein.
Classical Pathway
C1QA (Complement Component 1, Q Subcomponent, A Chain):
C1QB (Complement Component 1, Q Subcomponent, B Chain):
C1QC (Complement Component 1, Q Subcomponent, C Chain):
C1R (Complement Component 1, R Subcomponent):
| C1S (Complement Component 1, S Subcomponent): | C1S antibodies | C1S ELISA Kits | C1S Proteins |
| C4a - C4A: | C4a antibodies | C4a ELISA Kits | C4a Proteins |
| C4 - Complement 4: | C4 antibodies | C4 ELISA Kits | C4 Proteins |
| C4b - C4B: | C4b antibodies | C4b ELISA Kits | C4b Proteins |
Lectin Pathway
MASP1 (Mannan-Binding Lectin serine Peptidase 1 (C4/C2 Activating Component of Ra-Reactive Factor)):
| MBL2 (Mannose-Binding Lectin (Protein C) 2, Soluble): | MBL2 antibodies | MBL2 ELISA Kits | MBL2 Proteins |
| MASP2 (Mannan-Binding Lectin serine Peptidase 2): | MASP2 antibodies | MASP2 ELISA Kits | MASP2 Proteins |
| FCN1 (Ficolin (Collagen/fibrinogen Domain Containing) 1): | FCN1 antibodies | FCN1 ELISA Kits | FCN1 Proteins |
| FCN2 (Ficolin (Collagen/fibrinogen Domain Containing Lectin) 2 (Hucolin)): | FCN2 antibodies | FCN2 ELISA Kits | FCN2 Proteins |
| FCN3 (Ficolin (Collagen/fibrinogen Domain Containing) 3 (Hakata Antigen)): | FCN3 antibodies | FCN3 ELISA Kits | FCN3 Proteins |
Alternative Pathway
CFB - Complement Factor B
CFD - Adipsin
| C3 (Complement Component 3): | C3 antibodies | C3 ELISA Kits | C3 Proteins |
| C3b - Complement Fragment 3b: | |||
| CFH - Complement Factor H: | CFH antibodies | CFH ELISA Kits | CFH Proteins |
Terminal Pathway
C5 - Complement Component 5
| C5a - C5A: | C5a antibodies | C5a ELISA Kits | C5a Proteins |
| C7 (Complement Component C7): | C7 antibodies | C7 ELISA Kits | C7 Proteins |
| C8A (Complement Component 8, alpha Polypeptide): | C8A antibodies | C8A ELISA Kits | C8A Proteins |
| C8B (Complement Component 8, beta Polypeptide): | C8B antibodies | C8B ELISA Kits | C8B Proteins |
| C8G (Complement Component 8, gamma Polypeptide): | C8G antibodies | C8G ELISA Kits | C8G Proteins |
| C9 (Complement Component C9): | C9 antibodies | C9 ELISA Kits | C9 Proteins |
Regulators
CD55 (Complement Decay-Accelerating Factor):
CD59 (CD59):
| SERPING1 (Serpin Peptidase Inhibitor, Clade G (C1 Inhibitor), Member 1): | SERPING1 antibodies | SERPING1 ELISA Kits | SERPING1 Proteins |
| CFI - Complement Factor I: | CFI antibodies | CFI ELISA Kits | CFI Proteins |
| CR1 (Complement Component Receptor 1 (CD35)): | CR1 antibodies | CR1 ELISA Kits | |
| CFP (Complement Factor P): | CFP antibodies | CFP ELISA Kits | CFP Proteins |
| C4BPA (Complement Component 4 Binding Protein, alpha): | C4BPA antibodies | C4BPA ELISA Kits | C4BPA Proteins |
| C4BPB (Complement Component 4 Binding Protein, beta): | C4BPB antibodies | C4BPB ELISA Kits | C4BPB Proteins |
Extrinsic Pathway
F2 - Prothrombin
