Determination in the nanogram range of C1q in serum and unconcentrated CSF by electro-immunodiffusion

A new method for the determination of C1q in serum and cerebral spinal fluid (CSF) is described. The method has a sensitivity of 6 ng per assay or 1.2 mg/l. With this technique the mean value for C1q in normal human serum was 276 +/- 25 mg/l. The ratio of C1q in the blood compared with that in the CSF of normal individuals was more than 400: 1, since essentially no C1q could be detected in normal CSF. This ratio dropped considerably in some patients with neurological disorders, due to an increase in C1q levels in the CSF. Evidence is presented that these increased levels of CSF C1q are largely due to local synthesis of C1q rather than transudation of plasma C1q. This suggests that C1q in the CSF may serve as a marker of macrophage activity inside the central nervous system.