Localization of cylicin II in sperm cells. Calyx structures of human spermatozoa visualized by immunofluorescence microscopy using the serum of a multiple myeloma patient with a paraprotein specific for human cylicin II. The serum intensively decorates cylicin II, forming an equatorial belt around the sperm heads (red). The DNA dye DAPI was used to counterstain the nuclei.