[Incidence of circulating immune complexes in pediatric diseases. Comparative study with adults].

Circulating immune complexes were studied using 3.5% polyethyleneglycol precipitation in 312 children with various diseases whose ages ranged from 1 month to 14 years. One hundred and one patients (32.6%) were positive and the groups with the highest percentage were those with viral hepatitis (90%), sepsis (80.7%), collagen diseases (76.4%) and Schonlein-Henoch purpura (57.1%). We found immune complexes less frequently in idiopathic thrombocytopenic purpura than in published series of adult cases, possibly due to the fact that the diseases in children is due to a different pathogenetic mechanism. The composition of the immune complexes was tested by 1% agarose immunodiffusion against a panel of antisera. IgG and IgM were found most frequently, and IgA was very uncommon except in some cases of hepatitis. C4 was the most frequently found complement component, followed by C3. Important differences between the various diseases studied were noted. Our results are very similar to those previously published by other authors. Whereas serum autoantibodies and autoimmune diseases are less common in children than in adults, circulating immune complexes seem to have a similar frequency in children to that already reported for adults. It is difficult to assess the significance of circulating immune complexes. They might be (a) a mere "marker" of no pathogenic significance (b) a mechanism of tissue damage by intravascular deposition, or (c) they might interfere with the cell membrane receptors of macrophages, producing a defect in phagocytosis. However, we were unable to demonstrate an increased number of infections in these patients.