Immunocytochemical localization of a specific antigen in cell walls of Penicillium islandicum

Abstract

Immunofluorescence and immunogold labelling methods at the light and electron microscope levels respectively, were employed in order to determine the site(s) of binding of a monoclonal antibody PI01, specific for Penicillium islandicum , and raised in a previous study to soluble surface molecules of that fungus. By immunofluorescence labelling the PI01 antibody was localized at the walls of the vegetative hyphae but was not present in sporulating hyphae. By immunogold labelling the PI01 antibody was observed to bind to the outer wall layers in young actively-growing hyphae and at the interface between the outer pigmented and inner translucent wall layers in older hyphae and conidiophores. In conidiophores, the PI01-antigen appeared to diminish towards the distal ends of the metulae and the antigen was completely absent from phialides and conidia. We postulate that the specific antigen is an exoenzyme, possibly an autolysin and emphasise the importance of ultrastructural localization of antigens over immunofluorescence labelling techniques.