Fluorescent antibody localization of Microciona prolifera aggregation factor and its baseplate component

Specific rabbit antisera were prepared against purified aggregation factor and its membrane-associated receptor, baseplate, derived from the marine sponge. Microciona prolifera. They were utilized in conjunction with fluorescent-labeled goat anti-rabbit IgG in an assay to demonstrate the surface localizations of both components. The specificity of antibody preparations for AF and BP was demonstrated through inhibition of the rotation-mediated assay by homotypic antibody. This study confirms the presence of aggregation factor on the surface of disaggregated sponge cells maintained in the presence of the divalent cations, Ca++ and Mg++, and its absence when cells are maintained in Ca++ and Mg++-free seawater. The location of BP could also be demonstrated on the cell surface. Aggregation factors and baseplate appear to be heavily distributed on archeocytes and choanocytes, but are localized less intensely on gray cells. Gray cells are typified by yellowish autofluorescence of their intracellular granules in stained and control preparations. The reaction of anti-Microciona aggregation factor with its homotypic factor appeared to be species specificity judged by immunofluorescence assays and by inhibition of rotation-mediated assay by anti-homotypic AF since antibodies prepared against heterotypic AF preparations were unreactive.