84. Cohabiting with a sick mate: Relevance of olfactory contact to innate immune activity

Cohabitation with a sick cage-mate induced behavioral and immunological changes. Divergent signals including visual, olfactory, chemical, or tactile (Communication cues = CC) have been described as being involved in communication among individuals of the same and different species. This work was designed to analyze the effects of different CC on neutrophil activity (oxidative burst and phagocytosis). Female mice were paired and divided into one control (C) and one experimental (E) group. One mice of each E pair was inoculated i.p. with 5 X 106 Ehrlich tumor cells; the other animal of the pair, the object of this study, was not treated being referred to as “companion of sick partner” (CSP). One mouse of each C pair was called “companion of health partner” (CHP) remaining undisturbed; the other was injected with NaCl 0.9% (0.1 ml/10 g). Three experiments were done to analyze the effects of physical contact, olfactory and visual cues on neutrophil activity. Experimental mice were analyzed after fourteen days of cohabitation. Results showed that physical contact and visual cues were not relevant for neutrophil activity changes observed after cohabitation. On the contrary, the olfactory cures were fundamental for the decrease in neutrophil oxidative burst and phagocytosis. The present results strongly suggest that volatile compounds released by Ehrlich tumor-injected mice are perceived by their conspecifics, inducing the immune changes reported for cohabitation with a sick companion.