VISUALIZATION OF LECTIN-LIKE PROTEINS IN HUMAN PLACENTA BY MEANS OF ANTI-PLANT LECTIN ANTIBODIES

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 ag glutinin, Ulex europaeus agglutinin, and Phaseolus vulgaris leukoagglu tinin (PHA-L), as well as one antibody raised in goat against PHA-L. E ven at high dilutions of the primary antibody, strong staining was obt ained 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 immunohistochemic al patterns distinguishes with great clarity between the trophoblast c ell layers, thus relating to developmental and functional parameters; another localises PHA-L-immunoreactivity to the syncytiotrophoblast. T hese results underline the validity of the immunohistochemical screeni ng as an approach in its own right. Both positive and negative control s 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-L-like c ross-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-bin ding fractions of approximate molecular weights 32 kDa and 60 kDa. The 30 kDa fraction from placenta and the 32 kDa fraction from PHA-L anti gen bound lactosylated BSA but not fucosylated BSA. Taken together, th e immunohistochemical and biochemical data reveal the presence in the placenta of lectins, one of which resembles PHA-L not only antigenical ly but also in molecular weight and in sugar-binding specificity.