Olfactory stimuli and allo-recognition

Abstract

A number of species have demonstrated the ability to recognise related individuals by scent alone in a manner which may relate to their major histocompatibility (MHC) genotype. Further, the scent of the members of the opposite sex can activate aggressive responses, affect mating preference, induce oestrus, induce implantation delay or loss, augment early embryo survival and even alter the quality of the recipients immune defences. Two well known reproductive responses to pheromonal stimuli include the Whitten and Bruce effects. The “Whitten effect” is initiated by the presence of odours of an alien male, resulting in the onset of oestrus in un-mated female mice. The “Bruce effect” defines a complete pre-implantation block of pregnancy in mated females exposed to odours of an alien male. Conversely, if an alien male is introduced to a pregnant mouse on the day after implantation the incidence of spontaneous early embryo losses may be reduced. Therefore, neuroendocrine mediators induced by pheromonal messages derived from the resident male can alter the maternal cell-mediated immune response in the uterus to the fetal graft, dramatically affecting the outcome of pregnancy.