The specificity of serum antibodies to Giardia lamblia and to enterobacteria in gastrointestinal disease.

A comparative evaluation was made of immunofluorescent serum antibodies against Giardia lamblia and enterobacteria isolated from the upper intestine of patients with severe giardiasis. The study was carried out on sera from 51 patients belonging to seven intestinal disease groups. Antibodies against Giardia and against some enterobacteria were present in all eight cases of giardiasis with malabsorption, and absent in all five cases of invasive amoebiasis and in six normal control sera. Bacterial antibodies were found in the other five groups of intestinal disease, in 29 out of 38 cases. Giardia antibodies were found in only two of the other groups, tropical sprue (two cases) and coeliac disease (two cases). Thus Giardia antibodies may not signify active giardiasis but they were of restricted distribution and were sometimes present at relatively high titre. Bacterial antibodies were widely distributed but always at low titre. Absorption experiments indicated that the two types of antibody did not cross-react.