C1q deficiency is linked to autoimmune disorders

Human C1q ELISA: a reliable measurement

C1q: first step in classical complement activation

• C1q is an integral part of the first component of complement (C1)
• Formation of an antibody-antigen complex (immunocomplex) activates the classical pathway of the complement system. 
• C1q triggers the activation process by docking onto antibodies within these immunocomplexes
• C1q bridges the innate and adaptive immune systems
• Necrosis and apoptosis results in exposure of endogenous danger patterns, which can be directly recognized by C1q, thus activating the classical pathway
• Activated C1 cleaves complement proteins C2 and C4, resulting in the formation of C4bC2a, also called C3 convertase

C1q and diseases

• Deficieny of C1q is directly linked to Systemic Lupus Erythematosus (SLE) and glomerulonephritis due to homozygous congenital deletions
• Deficiency of C1q is associated with a higher risk of pyogenic infections
• Decrease in C1q serum levels results in reduced uptake of apoptotic cells
• The decrease of phagocytosis results in increased autoimmunity resulting in more circulating auto-antibodies

Matrix influences in human C1q ELISA

• Different matrices were evaluated in the human C1q ELISA
• Serum as well as plasma has to be diluted 200x to obtain reliable measurement (Fig 1)
• C1q in bronchoalveolar lavages (BAL) can be detected accurately when BAL is diluted at least 2x (Fig 2)
• No influence of anticoagulant was detected

Validation of human C1q ELISA

• C1q-depleted serum was spiked with purified C1q
• Recovery of spiked C1q was within the limits of 80-120% 
• No C1q was detected in C1q-depleted serum

Reference standard

• Purified C1q derived from Complement Technology Inc was used to validate our standard calculation (Fig 3)
• Perfect match between external C1q source and Hycult Biotech C1q (R2= 0.9997)

Specifications of human C1q ELISA (Cat.# HK356)

• Working time of 3.5 hours
• 100 µl sample/well
• Detection limit of 15.6 ng/ml
• Concentration range 15.6 – 1000 ng/ml
• Useful for serum,  plasma and BAL
• Detection of unbound C1q as well as C1q-immunocomplexes (CIC)
• Cross-reactive with mouse and rat C1q

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