Anti-immunoglobulin antibodies in children with Schönlein-Henoch syndrome. Absence of serum anti-IgA antibodies

Abstract

Circulating immune complexes (CIC) that simultaneously contain IgG and IgA are frequently found in IgA nephropathy (IgA-N) and the Schönlein-Henoch syndrome (SHS). The presence of anti-immunoglobulin antibodies (IgA anti-IgG and IgG anti-IgA) was studied by ELISA in the serum of 39 children with SHS and compared to 30 normal children. The mean level of IgG anti-IgA antibodies (240±104 u/ml) in SHS patients was similar to control values (251±85 u/ml); the IgA anti-IgG antibodies were increased, although only the antibodies against Fc fraction of IgG were elevated (185±71 u/ml in patients vs 127±24 μ/ml in controls,P<0.0001) without a significant increase of IgA anti-IgGFab antibodies (141±54 μ/ml vs. 137±25 u/ml); 16/39 (41%) of the patients had increased levels of IgA anti-IgGFc and 6 of these had also high IgA anti-IgGFab. None of these patients had high IgA anti-IgGFab antibodies without simultaneous augmentation of IgA anti-IgGFc. Only 3/39 (7.7%) of SHS patients showed high levels of IgG anti-IgA antibodies. The correlation of IgA anti-IgGFc antibodies with IgA anti-IgGFab was very strong (P<0.0001) but lower with IgG anti-IgA antibodies (P<0.002). In addition, 8/39 children had renal involvement, nevertheless in these patients the findings were quite similar, with a non-significant elevation of IgA anti-IgGF ab antibodies. These results show that the IgA anti-IgG antibodies are more frequently increased than IgG anti-IgA antibodies in the SHS; moreover they are mainly directed against Fc fraction and are IgA-FR isotype. Our findings suggest that the CIC in SHS are likely formed by the reaction of IgA antibodies against IgG and not vice versa.