The complement system, a crucial component of innate immunity, plays a multifaceted role in host defense, inflammation, and immune regulation. As research into complement-targeted therapies accelerates, the need for reliable and nuanced testing methods has become increasingly apparent. A range of specialized assays now enables scientists to evaluate complement activity with precision, supporting therapeutic development.
Hemolysis Inhibition Assay
Evaluating Inhibitor Potency Among the most informative tools for assessing complement inhibition is the hemolysis inhibition assay. This method measures the ability of therapeutic agents—such as anti-C5 antibodies or regulatory proteins like CD55 and CD59—to prevent red blood cell lysis triggered by the membrane attack complex (MAC). By quantifying the extent of inhibition, researchers can determine the functional efficacy of complement-targeting compounds. The assay supports both classical (CH50) and alternative (AH50) pathway analysis, offering flexibility for diverse experimental needs.
CH50 Functional Test Kit
Classical Pathway Assessment For laboratories focused on the classical complement pathway, the CH50 functional test remains a gold standard. This assay evaluates serum’s capacity to lyse antibody-coated erythrocytes, producing a CH50 value that reflects overall pathway activity. The test is widely used to detect complement deficiencies, monitor disease progression, and assess the impact of immunomodulatory treatments. Its compatibility with multiple species and consistent reproducibility make it a staple in both clinical and research settings.
Individual Component Activity Testing
Molecular-Level Insights While total complement activity offers a broad overview, dissecting the function of individual components provides deeper understanding. Quantitative assays such as ELISA, nephelometry, and radial immunodiffusion (RID) allow for accurate measurement of proteins like C3, C4, C5, Factor B, and Factor H. Functional assays further assess each component’s ability to restore hemolytic activity in deficient serum, offering critical insights into immune dysfunction and therapeutic mechanisms. This dual approach is particularly valuable in the study of autoimmune diseases, infections, and complement-mediated disorders.
One of the final products of the complement system is the membrane attack complex (MAC), which forms pores in the target cell membrane, leading to cell lysis and death. MAC formation represents the common terminal pathway of the complement system, involving a series of protein cleavage and activation reactions via the classical, alternative, or lectin pathways. Specifically, C5 is cleaved into C5a and C5b by C5 convertase. C5b binds with C6, followed by C7, forming the C5b67 complex, which inserts into the cell membrane. Subsequent binding of C8 forms the C5b678 complex, and multiple C9 molecules polymerize on C5b678 to form a ring structure, creating a complete membrane attack complex (C5b6789). Through this mechanism, MAC directly damages the cell membranes of various pathogens, including bacteria, virus-infected cells, and certain tumor cells.
The Complement System: Key to Immune Defense and Regulation
The complement system stands as a pivotal element within the innate immune system, orchestrating a series of responses aimed at identifying and eliminating pathogens while triggering inflammation. However, dysregulation of this system can lead to inflammatory and autoimmune disorders.
While the complement system is pivotal for immune defense, its imbalance can contribute to various diseases, including Paroxysmal Nocturnal Hemoglobinuria (PNH), Atypical Hemolytic Uremic Syndrome (aHUS), and complement-mediated kidney disorders such as membranous nephropathy and IgA nephropathy. PNH involves the absence of protective proteins (e.g., CD55 and CD59) on red blood cell surfaces, rendering them vulnerable to MAC attack, resulting in hemolysis and anemia. In aHUS, deficiencies in complement regulatory proteins lead to excessive complement activation, MAC deposition in glomeruli, endothelial cell damage, and thrombus formation. In complement-mediated kidney diseases, MAC deposition on the glomerular basement membrane can precipitate glomerular injury and decline in kidney function.
To mitigate the harmful effects of complement system activation, complement inhibitors have been developed, such as Eculizumab (Soliris) and Ravulizumab (Ultomiris). These are C5 inhibitors that prevent MAC formation by blocking the cleavage of C5, commonly used to treat PNH and aHUS. Other drugs, such as Avacopan, are C5aR1 antagonists primarily used for the treatment of ANCA-associated vasculitis and other diseases.
With ongoing research into the complement system and complement inhibitors, there is hope for developing safer and more effective therapies for a broader range of patients. The roles of C5a and MAC in the tumor microenvironment are also emerging areas of research, offering potential new avenues for cancer treatment. Overall, the complement system plays an indispensable role in immune defense and regulation, and deeper insights into its function and related therapeutics will aid in better understanding and treating various immune-related diseases.
A Trusted Partner in Complement Research
Creative Biolabs distinguishes itself through its commitment to scientific rigor, customization, and client support. Its complement testing platform is designed to meet the diverse needs of researchers, from early-stage drug discovery to translational immunology. By offering high-quality assays and expert guidance, Creative Biolabs enables scientists to explore the complexities of the complement system with confidence.
As the field of immunology continues to embrace personalized and targeted therapies, complement testing stands out as a vital tool for discovery and innovation. With robust methodologies and adaptable formats, researchers are better equipped than ever to explore the complexities of the immune system and translate findings into impactful treatments.
