Immunocytochemical localization of lysozyme in the nephrocytes of the harvestman, Leiobunum rotundum.

Nephrocytes are cells involved in the metabolism of hemolymph components and are characterized by peripheral finger-like projections bordering a labyrinthine channel system. The antibacterial protein lysozyme was localized in anterior and pericardial nephrocytes of the harvestman, Leiobunum rotundum, by biochemical and immuno-gold postembedding-labelling techniques. Lysozyme-activity was demonstrated in experimental animals, challenged by Micrococcus luteus Gram positive bacteria. With SDS-electrophoresis, lysozyme was proved to be present in nephrocytes adjoining the heart, before studies at the electron microscopical level were carried out. The opilionid lysozyme was found to have a molecular weight of 14,000 Da, thus belonging to the c-type lysozyme which is represented by hen-egg-white lysozyme. In untreated animals the presence of lysozyme could not be proved by electrophoresis. With immunogold labelling, however, lysozyme could be clearly localized in the vesicles of nephrocytes of untreated animals. Additional control experiments were carried out which revealed that the nephrocytes of L. rotundum in vivo are able to take up native lysozyme from an exterior medium. Therefore, the problem needs to be solved if nephrocyte vesicles transport lysozyme into or out of the cell.