The Ultrastructural Lesions Induced by Antibody and Complement in Rabbit Spermatozoa1

Abstract

Rabbit sperm were immobilized in 5 min after mixing with antibody (goat antisemen; antiepididymal sperm) and unheated complement (C′). Heated C′ was ineffective. Ultrastructural examination of the immobilized sperm revealed cell membrane damage, namely, rupture at the acrosomal apex. Otherwise, the trilaminar cell membrane structure was retained. 10-nm “holes” similar to those reported in lysed erythrocytes were not observed. Amorphous material coated both antibody and control goat globulin-treated sperm. At least in the case of the control, this may be related to the natural agglutinins for rabbit cells present in normal goat serum. Striking changes occurred in the outer acrosomal membrane (oAcm) of the immobilized sperm. These consisted of regularly spaced 60- to 200-nm holes through which the acrosomal material exuded. In extreme cases, the sperm cell membrane in the acrosomal region, the oAcm, and the acrosomal material were all absent exposing the inner acrosomal membrane of the immobilized sperm. Treatment with goat antiseminal plasma (antigen from vasectomized male) globulin plus C’ did not produce sperm immobilization or ultrastructural changes. The observations suggest that sperm immobilization results from antibody–complement rupture of the sperm cell membrane and a special reaction in the oAcm of the acrosomal apparatus.