Human milk containing specific secretory IgA inhibits binding of Giardia lamblia to nylon and glass surfaces.

The effects of human milk, containing specific secretory IgA, on the adherence of Giardia lamblia trophozoites in the presence and in the absence of intestinal mucus in vitro were studied. It was found that the trophozoites treated with breast milk, containing specific secretory IgA to G. lamblia, showed a significant decrease (p less than 0.01) in adherence to nylon fibre columns and glass surfaces than did trophozoites treated with milk containing no SIgA antibodies. The adherence to glass surfaces was significantly more (p less than 0.01) in the presence of intestinal mucus than when the mucus was absent. Milk that did not contain specific secretory SIgA to G. lamblia did not decrease the adherence to glass surfaces either in the presence or in the absence of mucus. The fluorescence study revealed the binding of specific secretory IgA on the trophozoite surface. The results suggest that binding of SIgA antibodies in milk to G. lamblia trophozoites inhibits parasite adherence, thus protecting against this infection in breast-fed babies.

Lectin activity of axenic and xenic Giardia lamblia trophozoites.

The membrane bound lectin of Giardia lamblia is though to play an important role in the selective colonization of the proximal small intestine by the parasite. The lectin obtained from xenic lysetes of G.lamblia gave a titre of more than 1:2048 in the hemagglutination test with rabbit erythrocytes, whereas the axenic lysates required pre-treatment with proteases (trypsin and pronase) in order to obtain a titre of 1:32. Similar behavior was exhibited by enterocytes of the mouse small intestine when tested for agglutination. The activation of xenic trophofzoites by the intestinal proteases and the probable role of bacterial enzymes has been discussed.

Effect of excretory-secretory products of Giardia lamblia on glucose and phenylalanine transport in the small intestine of Swiss albino mice.

The transport of D-glucose and L-phenylalanine was measured in intestinal brush border membrane (BBM) vesicles treated with Excretory-secretory (ES) products of Giardia lamblia. Uptake was found to be significantly lower (P/0.01) in the treated vesicles than in the controls. Exposure of intestinal tissue to ES products resulted in net secretion (P/0.01) of Na+, C1- and 3-O-methyl-D-glucose. Both observations indicate that alterations in the absorptive functions of the intestine might be attributed to interaction of ES products with the BBM.

Effect of different Giardia lamblia inocula on glucose and amino acids transport in the intestinal brush border membrane vesicles of infected mice.

The transport of D-glucose, L-phenyl-alanine, L-lysine and L-aspartic acid was measured in the brush border membrane vesicles prepared from intestines of Swiss albino mice infected with three different inocula of Giardia lamblia cysts (100, 1,000 and 10,000 cysts). A significantly low uptake of nutrients was observed in the infected animals as compared with the uninfected groups (P less than 0.05). However, the uptake of nutrients did not alter significantly with varying inoculum size. With D-glucose the respective peak uptakes at 30 seconds were 59.3 +/- 5.5, 60.4 +/- 3.8 and 60.5 +/- 4.02 pmoles mg-1 protein, while with L-phenyl-alanine they were 158.1 +/- 8.3, 151.7 +/- 17.3 and 140.7 +/- 6.0 pmoles mg-1 protein. The same trend was observed for L-lysine and L-aspartic acid. Therefore we conclude that inoculum size does not influence the uptake of nutrients.