C3 convertase (C4b-C2a) cleaves C3 into C3a and C3b. C3a goes into the plasma and C3b attaches to the red cell.
To detect in vitro binding, AHG serum needs to contain anti-C3b. [Some texts call anti-C3b by another name, anti-C3c: see below.]
Indirect Antiglobulin Test
In vitro (IAT with 15 - 60 min. incubation)
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| C3 convertase (C4b-C2a) cleaves C3 into C3a and C3b. C3a goes into the plasma and C3b attaches to the red cell. To detect in vitro binding, AHG serum needs to contain anti-C3b. [Some texts call anti-C3b by another name, anti-C3c: see below.] |
Direct Antiglobulin Test*
In vivo (DAT with incubation in the body for days)
Win increased incubation, C3b inactivator (INA) cleaves C3c from C3b, leaving mainly C3d on the red cell. To detect in vivo binding, AHG serum must contain anti-C3d.
Polyspecific antiglobulin serum contains anti-IgG, anti-C3b, anti-C3d.
Note: Red cells used for the DAT must be drawn into EDTA. EDTA chelates Ca++ (required for the Clqrs complex) and prevents complement from binding in vitro past Clq (even due to a harmless autoanti-I).
| Figure 2-12 |