fixed jejunal tissue sampleswere embedded in paraffin. Then, 3 μmsections
were cut and placed onto silanized slides. After deparaffinized in
xylene and rehydrated in decreasing concentrations of ethanol, the
slideswere placed in citrate buffer (pH 6.0) and subjected to microwave
for antigen retrieval. To block endogenous peroxidase activity, slides
were incubated with 3% H2O2 for 20 min at room temperature. After
being washed in phosphate buffer saline (PBS, 0.01 M pH 7.2), the sections
were incubated in normal rabbit serum for 30 min. Subsequently,
rabbit anti-pig sIgA polyclonal primary antibodies (Invitrogen) was diluted
1:100 in PBS buffer (0.01 M, pH 7.2) and incubated overnight at
4 °C. Thereafter, the sections were incubated with a biotinylated secondary
goat anti-rabbit antibody for 10 h at 4 °C, followed by a 45-
min incubation with avidin-biotin complex (ABC) reagent for 30 min
at roomtemperature. The sectionswerewashed three times in PBS during
all incubations. 3,3′-diaminobenzidine (DAB) was used as substrate
to visualize the bound antibodies and the sections were counterstained
with hematoxylin and mounted with glycerol gelatin. Finally, the sections
were imaged using a Leica DMIRB microscope (Leica, Germany),
and the image of each slice at least in 5 different fields was analyzed.
The average integrated optical density of the positive products was detected
by using the Image-pro plus software (version 6.0 forWindows)
at 200× magnification.