Complement Anaphylatoxin

Complement anaphylatoxins—C3a, C4a, and C5a—are potent bioactive peptides generated during complement system activation. These molecules serve as critical mediators of immune responses, bridging innate and adaptive immunity while modulating inflammatory pathways. At Creative Biolabs, our two decades of expertise in complement therapeutics have positioned us at the forefront of research and innovation targeting these dynamic molecules.

What is an Anaphylatoxin?

Friedberger discovered that C5a, a cleavage fragment of complement C5, could be toxic to guinea pigs in 1910, so he called C5a anaphylatoxin. In 1967, researchers also found that C3 cleavage fragment C3a also has similar activity. Since then, in 1979, another weakly active anaphylatoxin C4a was also discovered. Therefore, there are three types of anaphylatoxin that have been found and confirmed, namely C3a, C4a and C5a.

Fig. 1 Molecular models of human C3a, C4a, and C5a.^1,3

C3a, C4a and C5a are produced by cleavage near the N-terminus of the κ chains of complements C3, C4 and C5, respectively. They are all small molecular peptides, conformationally stable, pH resistant (pH 1-12), and heat resistant. These anaphylatoxins can bind to corresponding receptors on the surface of mast cells and basophils, stimulate cell degranulation, release active mediators such as histamine, and cause symptoms such as vasodilation, increased permeability, smooth muscle contraction, bronchospasm and other symptoms.

Structural Characteristics of Anaphylatoxins

Anaphylatoxins are active fragments produced by proteolytic cleavage of complement proteins C3, C4 and C5, with a highly conserved molecular architecture and a stable bioactive structure.

Table 1 Basic structural features of anaphylatoxins.

In summary, the core features are as follows:

• Conserved disulfide bonds: Six cysteine residues form three intra-chain disulfide bridges, stabilizing the core region essential for biological activity. Activity strength: C5a > C3a > C4a.
• α-helical domains: Circular dichroism studies reveal 40–50% α-helix content, critical for receptor binding and signaling.
• Receptor-binding motifs: The C-terminal pentapeptide of C3a/C5a directly interacts with G-protein-coupled receptors (C3aR, C5aR1).

Structural disruptions (e.g., disulfide bond cleavage) significantly impair activity, highlighting the importance of conformation in function.

Biological Functions of Anaphylatoxins

C3a, C4a, and C5a play multidimensional roles in innate and adaptive immunity by activating specific receptors and modulating immune cell activity. Their functional mechanisms can be categorized into the following core directions.

Innate Immune Modulation

Adaptive Immunomodulation

Fig. 2 The anaphylatoxins impact on intrinsic T cell and DC-mediated activation.^{2, 3}

Table 2 Comparative functions.

Anaphylatoxin Test

Creative Biolabs is one of the world's largest suppliers of complement testing, providing customers with high-quality complement activation product test services from diagnostics to drug development. Complement activation products include split fragments after enzymatic cleavage of certain components, such as C4 (C4a and C4d), C3 (C3a and C3d), factor B (Bb), C5 (C5a).

Detection of complement anaphylatoxins usually involves a variety of experimental techniques to accurately assess its level and function in an organism. The following are some of the common assays:

• ELISA: Use anti-neoepitope antibodies as capture antibodies to directly capture activated fragments without interference from inactivated components.
• Flow Cytometry: Indirectly assess the activity of allergenic toxins by detecting the expression level of cell surface receptors.
• PC Biosensors: Utilize photonic crystal technology to detect changes in cell morphology or adhesion, reflecting cell activation status.
• Mass Spectrometry: Direct detection and quantification of the presence of allergy toxins by liquid chromatography-mass spectrometry (LC-MS) technology.

Pathophysiological Roles and Disease Associations

Anaphylatoxins are key mediators of immune defense under physiological conditions, but its excessive or dysregulated activation can lead to a variety of diseases. Its effects are bi-directional.

Table 3 Mechanisms of different anaphylatoxins in disease.

Creative Biolabs pioneers innovative approaches to modulate anaphylatoxin pathways:

• Receptor antagonists: C5aR1 inhibitors, C3aR blockers
• Neutralizing antibodies: Anti-C5a monoclonal antibodies
• Enzymatic inactivation: Rapidly degrades circulating C3a/C5a

Solutions Provided by Creative Biolabs Targeting Anaphylatoxin-related Diseases:

Creative Biolabs Provides High-quality Anaphylatoxin Related Products.

• High-purity anaphylatoxin proteins: For in vitro assay development and drug screening.
• Customized antibody production: Targeting C3aR, C5aR1, or specific anaphylatoxin epitopes.

If you want more information, please feel free to contact us.

References

1. Pasupuleti, Mukesh, et al. "Preservation of antimicrobial properties of complement peptide C3a, from invertebrates to humans." Journal of Biological Chemistry 282.4 (2007): 2520-2528. https://doi.org/10.1074/jbc.M607848200
2. Schanzenbacher, Jovan, Jörg Köhl, and Christian M. Karsten. "Anaphylatoxins spark the flame in early autoimmunity." Frontiers in Immunology 13 (2022): 958392. https://doi.org/10.3389/fimmu.2022.958392
3. under Open Access license CC BY 4.0, without modification.

• Complement Receptors of Complement System: CR1
• Complement Receptors of Complement System: CR2
• Complement Receptors of Complement System: ITGAM
• Complement Receptors of Complement System: ITGAX
• Complement C1q Receptor
• Complement Receptor of the Immunoglobulin Superfamily/CRIg
• Anaphylatoxin Receptors