C3 Nephritic Factors (C3Nefs) Test

C3 nephritic factors (C3NeFs) are associated with renal disease, dense deposit disease, partial lipodystrophy, post-streptococcal glomerulonephritis, systemic lupus erythematosus, and meningococcal meningitis. It plays a very critical role in the development of these diseases. C3NeFs test helps to diagnose and study the occurrence and development of these diseases. Creative Biolabs has many years of experience in C3NeFs testing. Our dedicated team can provide the highest quality C3NeFs testing services to customers from all over the world to meet their needs.

Introduction of C3Nefs

Nephritic factors (NFs) comprise a heterogeneous group of autoantibodies against neoepitopes generated in the C3 and C5 convertases of the complement system, causing its dysregulation. C3Nefs are IgG and IgM autoantibodies that bind directly to C3 convertase (C3bBb) of the AP. Most C3Nefs recognize the neoepitope on the C3bBb complex and stabilizes it, but some of them can also bind C3b or Bb alone. Stabilization of the C3bBb convertase by C3Nefs results in higher and prolonged activity, C3 and C5 consumption and activation of the terminal pathway. C3Nefs stabilize the convertase, significantly increasing its half-life, and inhibit accelerated decay mediated by FH, DAF, and CR1. Many research reported that some C3Nefs require the presence of properdin and others are properdin independent, separating C3NeFs into properdin-dependent and -independent groups with different effects in vivo. In addition, some C3NeFs stabilize the C5 convertase, causing C5 consumption and terminal pathway activation.

C3Nefs Tests

Modern tests are based on measuring the binding of NFs to the preformed C3 convertase (binding assays) or measuring C3 convertase activity (functional assays). The binding assays measure the capacity of C3Nefs to bind and stabilize the C3 convertase of AP, whereas functional assays measure C3 cleavage by immunofixation electrophoresis, hemolytic assays (HA) or other methods.

1. Binding Assays

There are several procedures described for the detection of C3Nefs. Typically, C3b is immobilized on the microplate surface and then reacted with FB and FD. High yields of microplate attached convertase complexes are achieved by the addition of NiCl₂ or NiSO₄. The most widely used binding assays are enzyme-linked immunosorbent assays (ELISAs), including C3 convertase stabilization ELISA (COS), C3 convertase with added properdin ELISA (COS-P), C3Nef IgG-binding ELISA (CO-Ig). COS and COS-P are used to detect plate-bound Bb fragments with a polyclonal antibody, while CO-Ig is used to detect immunoglobulins bound to preformed convertase complex.

1. Functional Assays

   Functional assays generally involve three methods, as follows:

   1. Immunofixation electrophoresis: the functional activity of C3Nefs can be determined through quantifying complement activation products (mostly C3 fragments) by two-dimensional immunoelectrophoresis, immunofixation electrophoresis or western blotting.
   2. HA: the primary method for the detection of C3Nefs activity is the HA test, which measures the lysis of sheep (SE)/rabbit erythrocytes (RE). In these tests, purified complement components are added to perform convertases on the surface of SE sensitized with anti-sheep antibodies (EA). Later, purified FB and FD are added to form specifically AP convertase. C3Nefs activity is measured by the incubation of SE with a mixture of normal human serum (NHS) and patient's serum. Considering that RE could be lysed by human serum, it is necessary to block the terminal pathway using C5 blockers when measuring the lysis of RE.
   3. Other methods: another option to measure C3Nefs activity is through the quantification of anaphylatoxins C3a (Fig.1).

Fig.1 Diagnostic tests for the detection of nephritic factors (NFs). (Corvillo, 2019)

Our Service of C3Nefs Tests

Creative Biolabs is the leading provider of complement testing services. Our extensive and professional complement testing services have earned a good reputation and we helped our clients complete a large number of complementary testing services, significantly accelerating their project progress. We offer a wide variety of functional tests of complement activity, including measures of complement proteins and their activation products, the detection of autoantibodies to different proteins and/or protein complexes. In terms of C3Nefs testing, we have multifunctional detection technology and a variety of advanced equipment, which enables us to provide customers with quality C3Nefs testing services.

Our advantages:

1. Easy to perform and reproducible results
2. Fast turnaround time
3. Detailed analysis report and expert interpretation

If you have any questions about our testing services, please feel free to contact us.

Reference
1. Corvillo, F.; et al. Nephritic Factors: An Overview of Classification, Diagnostic Tools and Clinical Associations. Front Immunol. 2019, 10: 886.

• Anti-C1q Autoantibody Test
• Anti-C3 Autoantibody Test
• C1 Inhibitor Autoantibody Test
• Anti-factor H Autoantibody Test
• Anti-factor B Autoantibody Test