Visualization of lectin-like proteins in human placenta by means of anti-plant lectin antibodies

Abstract

Proteins antigenically cross-reactive with lectins were sought in the placenta by immunohistochemistry using polyclonal antibodies raised in rabbit against four well-known lectins: Concanavalin A, Wheat germ agglutinin, Ulex europaeus agglutinin, and Phaseolus vulgaris leukoagglutinin (PHA-L), as well as one antibody raised in goat against PHA-L. Even at high dilutions of the primary antibody, strong staining was obtained after short incubations, in patterns generally resembling those obtained for placental lectins by other means, such as those based on binding capacity for glycosylated probes. One of the immunohistochemical patterns distinguishes with great clarity between the trophoblast cell layers, thus relating to developmental and functional parameters; another localises PHA-L-immunoreactivity to the syncytiotrophoblast. These results underline the validity of the immunohistochemical screening as an approach in its own right. Both positive and negative controls were applied to the immunohistochemical methodology. These controls showed that the staining patterns obtained relate to the specificities of the primary antibodies employed; i.e. to lectins. The PHA-Llike cross-reactivity was analysed immunochemically. In electrophoretically separated and Western-blotted placental extracts there were found anti-PHA-L-binding fractions of apparent molecular weights 30 kDa, 58 kDa and 67 kDa. Control studies of the PHA-L antigen showed anti-PHA-L-binding fractions of approximate molecular weights 32 kDa and 60 kDa. The 30 kDa fraction from placenta and the 32 kDa fraction from PHA-L antigen bound lactosylated BSA but not fucosylated BSA. Taken together, the immunohistochemical and biochemical data reveal the presence in the placenta of lectins, one of which resembles PHA-L not only antigenically but also in molecular weight and in sugar-binding specificity.