Do human spermatozoa reactivate in the cytoplasm of somatic cells?

The morphological changes following Sendai virus-enhanced interaction of purified fractions of human spermatozoa with various types of fibroblast lines were examined over a period of several days. The incorporation of spermatozoa was monitored by a variety of immunofluorescent staining techniques, including one for protamin. The initially high incorporation frequency (30--40%) was accompanied by swelling of the acrosome and nucleus, which, in most instances, was followed by gradual lysis of the sperm components. However, a small proportion of all incorporated spermatozoa (2%) exhibited chromatin decondensation, accompanied by a shift from a protamin to histone content and induction of RNA and DNA synthesis. These latter cells appear to fit the criteria for true reactivation and electron-microscope studies show that they do not undergo phagocytosis as do the majority of incorporated spermatozoa.