Occurrence of specific secretory immunoglobulin A in bile after inoculation of Giardia lamblia trophozoites into rat duodenum.

We studied the appearance of specific secretory immunoglobulin A (IgA) antibody in bile after inoculation of live Giardia lamblia trophozoites into rat intestine. Serial bile specimens collected before and after inoculation of trophozoites were assayed for IgA antibodies by indirect immunofluorescence. Secretory IgA antibodies to Giardia lamblia were first detected in bile at 3 days after inoculation, remained elevated through 12 days, and then returned to control levels. Positive immunofluorescence of trophozoites for IgA was observed at bile titers of 1:80 to 1:160, whereas control biles were usually negative at dilutions of 1:10 or less. Scanning electron microscopic examination of Giardia in conjunction with immunocytochemistry revealed IgA antibodies bound to the flagella and surfaces of the trophozoites including the adhesive disk. These data demonstrate the occurrence of a secretory IgA immune response directed against surface antigens of Giardia lamblia trophozoites in the rat.