However, there have been reports of classical class I MHC antigens in true solution in the body fluids of mousel, man and rat. The function of these soluble molecules is unknown. Behavioural studies showed that untrained PVR-RT1u rats could distinguish between urine odours of male rats of the PVG and PVG.RL that differ only in the alleles at RT1.A. Experiments designed to investigate the mechanism underlying the ability of animals to discriminate MHC types has shown that intact Class 1 antigens are not the odouriferous component in the urine. An indirect mechanism for producing MHC-related odours by the action of immune responses, restricted by MHC Class 1 molecules, to bacterial populations in the commensal flora was also investigated.
Bacterial flora seem to be necessary for the allele specific odour.
Work to be dicussed by others speakers shows that while bacterial flora is necessary for allele-specific odours they are not sufficient. Instead, there is likely to be an interaction between excreted Class 1 molecules and odourants derived from bacterial flora.