C1 subcomponent conplexes in normal and pathological sera studied by crossed immunoelectrophoresis

Area of Science:

• Immunology
• Biochemistry
• Complement System

Background:

• The complement system is crucial for innate immunity.
• C1 complex, comprising C1q, C1r, and C1s, initiates the classical pathway.
• Understanding C1s protein species and their functions is vital for complement research.

Purpose of the Study:

• To characterize molecular species of C1s protein in normal and pathological human sera.
• To investigate the composition and potential function of different C1s complexes.
• To explore the activation mechanisms of C1 subcomponents during electrophoresis.

Main Methods:

• Crossed immunoelectrophoresis in the presence of calcium.
• Analysis of C1s protein species in pathological and normal sera.
• Electrophoretic separation and elution of C1 complexes.

Main Results:

• Pathological sera exhibited three C1s species (origin, beta1, alpha2), while normal sera showed two (origin, alpha2).
• The origin peak represented macromolecular C1; the alpha2 peak was a preformed C1 complex (C1 IA, C1s, C1r) lacking C4 cleaving activity.
• A novel beta1 region species was identified as a calcium-dependent C1r-C1s complex, likely a proenzyme, which formed macromolecular C1 upon C1q addition and exhibited C1s activity after activation.

Conclusions:

• Distinct C1s molecular species exist in serum, varying between normal and pathological states.
• A calcium-dependent C1r-C1s complex (beta1 species) is identified as a potential proenzyme form of C1.
• Electrophoresis can initiate C1 subcomponent activation, generating C1s activity from macromolecular C1 and the beta1 complex.