Impaired IgA response to Giardia heat shock antigen in children with persistent diarrhoea and giardiasis.

The serum antibody response in Gambian children with persistent diarrhoea and giardiasis has been studied. Total serum IgG, IgA, and IgM concentrations were increased in these patients as compared with controls from the same area. Determination of the concentrations of Giardia specific antibodies by enzyme linked immuno adsorbent assay (ELISA), however, revealed that only IgM was raised while those of IgA and IgG were similar to the controls. Analysis of the antigenic determinants of the IgG and IgA responses by immunoblotting showed that patients with chronic infection unlike those who clear the infection have no IgA response to a 57 kDa Giardia heat shock antigen. The association of high concentrations of Giardia specific IgM, low concentrations of Giardia specific IgA and IgG and inability to clear the infection suggests that the switch from an IgM to an IgG or IgA response is inefficient.