AP50

Sceening test for the diagnosis of complement deficiency.

The complement system consists of a system of plasma proteins that can be activated on the surfaces of microorganisms. It was originally discovered as a complementary part of the antibody response (see Immunity, Acquired).

However, it is also involved in the reaction processes of innate immunity.

The complement system consists of > 30 complement proteins with partly inducible enzymatic activity as well as receptor proteins and regulatory proteins. They are present in the blood plasma dissolved or cell-bound. These proteins are designated with C and atomic number (e.g. C1; C2 etc.).

C3 is a central component of the complement system and is produced by resident tissue cells such as keratinocytes. The individual complement factors serve, among other things, to defend against microorganisms (e.g. bacteria, fungi, parasites; see also immunodeficiencies primary (complement defects).

The AP50 test works in the same way as the CH50 test. In contrast to this, sensitized rabbit erythrocytes are used and the formation of the C3 convertase is prevented. This activation pathway is Ca2+-dependent and is inhibited when the incubation mixtures of the AP50 assay are free of Ca2+. The AP50 assay is dependent on sequential activation of factors D, B, P, C3, C5, C6, C7, C8, and C9.

The activity of individual complement proteins can be determined in a similar way to the determination of individual factors of the coagulatory system, using deficiency plasmas lacking the complement protein of interest. Constant amounts of deficient plasma are incubated with increasing amounts of patient plasma.

1. https://www.labor-und-diagnose-2020.de/