Immunological cross-reactivities between proteins secreted by the subcommissural organ, and plant lectins

The glial subcommissural organ (SCO) discharges a glycoprotein-rich secretory product into the third ventricle to form Reissner's fibre (RF). The SCO proteins bear N-linked oligosaccharides, such as mediate many cell-cell and cell-matrix interactions. In such interactions the corresponding partner molecule recognising the sugar chain is often a sugar-specific protein (lectin). We present here evidence that the constituents of the SCO secretory product include proteins immunologically cross-reactive with certain plant lectins. Polyclonal antisera directed against Phaseolus vulgaris agglutinin-L (PHA-L) labelled the apically released RF-material of the rat SCO. Indirect ELISA studies shows in addition that anti-RF antisera bound to certain plant lectins (PHA-L, Con A). Dot spot assays demonstrated binding of anti-PHA-L to RF proteins. In Western blots of RF proteins anti-PHA-L, anti-RCA and anti-Con A bound to distinctive subsets of the RF protein fractions.