Cross-reactivity among different Giardia lamblia isolates using immunofluorescent antibody and enzyme immunoassay techniques.

Rabbit antisera to 11 Giardia lamblia isolates were reacted with 8 G. lamblia isolates using single antibody ELISA and indirect immunofluorescent antibody techniques (IFA). Using living trophozoite organisms, IFA showed marked surface fluorescence with homologous antisera-organism pairs while heterologous pairs showed reduced or no reactivity. Using formalin-fixed trophozoites, the pattern of fluorescence changed to include diffuse internal fluorescence with both homologous and heterologous pairs. In contrast to the variability in surface fluorescence, similar reactivity was noted for homologous and heterologous antisera-isolate pairs with the ELISA. In addition, a double antibody enzyme immunoassay using rabbit antisera prepared to 2 G. lamblia isolates was performed with 8 different isolates as test antigen. All 8 were equally well detected. These data confirm previous findings that G. lamblia isolates have both different and common antigens. The different antigens appear to be on the surface of the organism while the common antigens appear to be internal or somatic.