Amyloid P-component(C1t) and complement: Lack of physical or functional relationship

Studies were carried out to determine if Clt, which is identical to the P-component of amyloid (AP), plays a role in Cl structure or function, or modulates the activity of Cl or its sub-units. Analyses of Cl in serum by a direct immunodiffusion method showed conclusively that AP was not a constituent of Cl. Further, AP did not interact physically with Cl or with Clq, Clr or Cls individually or in any combination, nor did it activate precursor Cl. Although some preparations contained Cl r-like hemolytic activity, this was due to the variable presence of a contaminating serine esterase, with properties suggesting that the contaminant was Clr. AP was also completely devoid of ability to provide Clr-like activity to sera genetically deficient in Clr. Immunodepletion studies showed that AP was not essential for hemolytic activity. As reported by others, Ap formed a calcium-dependent bond with agarose. In addition, AP interacted with IgG and aggregated in the presence of calcium. These studies cumulatively demonstrate that AP is not a sub-component of Cl and further show that AP does not interact with, or modulate the activity of Cl or any of its sub-units. The present experiments also furnish alternative explanations for earlier studies which led to the conclusion that AP was a fourth Cl subcomponent.