IgG4 antibodies in Egyptian patients with schistosomiasis.

Serum immunoglobulins were determined in 40 Egyptian patients with schistosomiasis. In addition to the well-established elevation in total IgE, a striking imbalance in the IgG subclass levels was found: IgG3 and IgG4 levels were markedly elevated, whereas IgG2 levels were normal. The IgG4 level did not correlate with the IgG3 level, but a weak correlation between the IgG4 levels and the logarithmic value of the IgE levels was observed (r = 0.49). We determined anti-schistosome antibodies in the IgE and IgG classes and in the IgG4 subclass by a RAST-type of assay. As test antigens an adult worm antigen preparation (AWA) and a soluble egg antigen preparation (SEA) were used. IgE antibodies reacted predominantly with AWA, whereas IgG4 antibodies, especially in patients with recent infections, were directed mainly against SEA. The hypothesis is put forward that the IgG4 antibodies interfere with the effector activities of anti-schistosome antibodies, and thus inhibit complement activation and mast cell triggering.