C1 SUBCOMPONENT COMPLEXES IN NORMAL AND PATHOLOGICAL SERA STUDIED BY CROSSED IMMUNOELECTROPHORESIS

Abstract

Selected pathological sera gave three molecular species of C1s protein on crossed immunoelectrophoresis in the presence of calcium. Cls precipitates were obtained at the origin and in the β₁ and α₂ regions. 12 normal sera gave C1s protein peaks at the origin and in α₃ position. One of the normal sera also contained a small amount of the β₃ C1s protein. The Cls protein at the origin represented macromolecular C1. The α₂ peak was a complex composed of CI IA, C1s and C1r proteins. This complex was preformed in serum and did not show C4 cleaving activity. The molecular species in the β₁ region was shown to be a calcium-dependent complex of C1r and C1s, probably in proenzyme form. The C1r-C1s complex formed macromolecular C1 on addition of purified C1q to serum. During electrophoresis activation of C1 subcomponents was initiated by a mechanism involving C1r with generation of C1s activity in eluted fractions corresponding to the position of macromolecular C1 as well as in the β region. The significance of β₁ C1s complexes or of α₂ C1s complexes in normal and pathological sera was discussed.