Anticomplementary activity in multiple sclerosis

Anticomplementary activity (ACA) is a common problem in serological work. Often it is regarded as an indicator of circulating immune complexes and has been clinically used as such. In a longitudinal study (Ryberg 1982b) ACA was determined in heated (56 degrees C for 30 min) sera from 35 MS patients followed for up to 5 years; in 18 of them ACA in heated CSF was also assayed. Persistent or transitory ACA of low titre was found in some sequences, usually without evident correlation with clinical events. Marked ACA in unheated sera was found more often in MS patients than in controls and showed dramatic changes in most of 15 sequences studied for this property, sometimes in a way suggesting a correlation with clinical exacerbations. This activity was heat labile and was not bound by an immunosorbent with affinity to human IgG and, therefore, is not likely to represent IgG containing aggregates or immune complexes.