Transmucosal transport of phytohemagglutinin, concanavalin A and alpha-lactalbumin across rabbit ileum in vitro.

The transmucosal passage of alpha-lactalbumin (alpha-La), phytohemagglutinin (PHA), and concanavalin A (Con A) (1 mg/ml) was measured in the rabbit ileum mounted in the Ussing chamber, with and without 10(-2) M glucose or galactose. The transport of the radiolabelled proteins was assessed by radioisotopic determination, high pressure liquid chromatography (HPLC) and enzyme linked immunosorbent assay (ELISA). In the absence of galactose, the transmucosal transport was significantly higher for PHA (4.1 +/- 1.8 micrograms/h.cm2 mean +/- SE) than for alpha-La (2.9 +/- 1.2) and very low for Con A (0.6 +/- 0.5). HPLC analysis of the transported material revealed differential processing of the proteins. ELISA indicated that 3 percent of radiolabelled alpha-La that crossed the epithelium was in an immunoreactive form, whereas no immunoreactive forms of PHA and Con A were detected. The uptake or binding by the tissue was identical for PHA and Con A (7.8 +/- 2.9 and 5.8 +/- 2.8 micrograms/cm2, respectively), and significantly lower for alpha-La (1.5 +/- 0.31). 10(-2) M galactose did not modify the uptake or binding of alpha-La and Con A, but significantly decreased that of PHA to a level that was not significantly different from that of alpha-La. The present results indicate that the initial uptake of the proteins is most likely dependent upon their interactions with the luminal side of the epithelium. After uptake, the proteins are subjected to intracellular processing which also appeared differential. Thus, protein transport depends on the properties both of the compartment crossed (Glycocalyx, brush-border membrane, cytoplasm, basolateral membrane), and of the protein.