Mustelus canis,the smooth dogfish shark as a model for immunoprivileged sites in yolk sac placentation and sperm storage

Placental viviparity and sperm storage make their first appearance in the vertebrate line in Chondrichthyes, the oldest extant jawed vertebrates. Although viviparity is advantageous for nourishment and growth of the offspring, it involves an immunological risk for sperm containing paternal antigens and the placenta containing fetal antigens. The placental smoothhound shark, Mustelus canis, has yolk sac placentation and stores sperm throughout the year in sperm storage tubules (SST) of the terminal zone (TZ) in the oviducal gland (OG) in the female. This animal has been used as a model to examine the uteroplacental complex and SST. Techniques used were transmission electron microscopy and immunohistochemistry to investigate the tissue expression of the cytokines interlukin 1 (IL-1) α, IL-1 β, its specific membrane receptor, IL-1 receptor type I (IL-1R tI) and macrophage migration inhibitory factor (MIF). In addition the uteroplacental complex has been profiled as to the diversity of its glycosylation, which was found to be as complex as that found in both reptilian and mammalian placenta. Immunostaining of the uteroplacental complex for IL-1 α, IL-1 β, IL-R tI revealed by binding leucocytes of both the mother and fetus. Yolk sac endoderm was also positive for all the epitopes studied while ectoderm was positive only for IL-1 α. Immunoreactivity in the uterine endometrium was obtained for IL-1 α and its receptor while the egg envelope was always negative. Placenta and SST were positive for MIF and IL-1 receptor. The present findings on the expression of the interleukin system and MIF in the uteroplacental complex and SST suggest that these cytokines are involved in evolutionarily conserved immunological mechanisms that anticipate the presence of paternal and fetal antigens in maternal tissues.