Interactions among the MHC, Diet and Bacteria in the Production of Social Odors in Rodents

Abstract

Many mammals can be identified by their individual odors or “olfactory fingerprints” (Brown, 1979) and these individual odors have been linked to genetic differences at the major histocompatibility complex (MHC) in both laboratory mice (Yamazak et al., 1991) and rats (Brown et al., 1987). The MHC regions of the mouse and rat have a similar organization (Brown et al., 1990), each having three different regions, each of which contributes to the individual’s body odor (Brown et al., 1989; Yamazaki et al., 1990a). The MHC, however, is not the only genetic region which contributes to individual odors. The sex chromosomes and the background genes (i.e., non-MHC regions) also contribute to the individual odors of mice (Yamazaki et al., 1986; Beauchamp et al., 1990). Since the class I MHC antigens are found in the urine of rats (Singh et al., 1987, 1988; Roser et al., 1991), we hypothesized that the class I antigens themselves might be the source of the odor of individuality, but this is not the case as removal of the class I antigen from the urine of rats did not remove the individuality signal (Brown et al., 1987). While the intact MHC class I antigens do not appear to be the source of the odor of individuality, it is possible that volatile fragments of these antigens or other volatiles attached to these antigens may provide individually unique odors in the urine.