Solubilization of immune complexes and inhibition of immune precipitation in SLE sera

The ability of serum to in vitro process immune complexes both preformed (ICSC) and during their formation (ICPIC) has been evaluated in 37 patients affected by systemic lupus erythematosus (SLE). ICSC was found to be significantly lower in these patients than in normal controls (p less than 0.001), and strictly related to the phase of the disease. Correlations were evidenced between ICSC and haemolytic activity of the classical and alternative pathways of complement, levels of the complement components C3 and C4, and incidence of circulating immune complexes. Low values of ICPIC were demonstrated almost only in sera of patients with active SLE; in fact, ICPIC was impaired in 6 sera only, and five of them were collected in the acute phase. All sera with decreased ICPIC also displayed a very low level of the C4 complement component.