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Previous studies in animals and humans show that genes in the major histocompatibility complex (MHC) influence individual odours and that females often prefer odour of MHC-dissimilar males, perhaps to increase offspring heterozygosity or reduce inbreeding. Women using oral hormonal contraceptives have been reported to have the opposite preference, raising the possibility that oral contraceptives alter female preference towards MHC similarity, with possible fertility costs. Here we test directly whether contraceptive pill use alters odour preferences using a longitudinal design in which women were tested before and after initiating pill use; a control group of non-users were tested with a comparable interval between test sessions. In contrast to some previous studies, there was no significant difference in ratings between odours of MHC-dissimilar and MHC-similar men among women during the follicular cycle phase. However, single women preferred odours of MHC-similar men, while women in relationships preferred odours of MHC-dissimilar men, a result consistent with studies in other species, suggesting that paired females may seek to improve offspring quality through extra-pair partnerships. Across tests, we found a significant preference shift towards MHC similarity associated with pill use, which was not evident in the control group. If odour plays a role in human mate choice, our results suggest that contraceptive pill use could disrupt disassortative mate preferences.

Individuals tend to choose mates who are sufficiently genetically dissimilar to avoid inbreeding. As facial attractiveness is a key factor in human mate preference, we investigated whether facial preferences were related to genetic dissimilarity. We asked female volunteers to rate the attractiveness of men from photographs and compared these results with individual genotypes at the major histocompatibility complex (MHC). In contrast to previously reported preferences based on odour, we found a non-significant tendency for women to rate MHC-similar faces as more attractive, suggesting a preference for cues to a self-similar MHC in faces. Further analysis revealed that male faces received higher attractiveness scores when rated by women who were MHC-similar than by MHC-dissimilar women. Although unexpected, this MHC-similar facial preference is consistent with other studies documenting assortative preferences in humans, including for facial phenotype.

There is increasing evidence that DSA are associated with poor graft survival, although there are little data in children. We aimed to describe the incidence of DSA in this group and to determine correlation with graft survival. HLA antibodies were analysed in 59 paediatric cardiac transplant recipients. Mean age 10.4 (0.7-18.5) yr, mean time post-transplant 5.1 (0.3-17.3) yr. Antibody detection/identification was performed on the Luminex platform with subsequent identification using Lifescreen Identification kits/One-Lambda Single antigen kits. Forty patients (69%) had no HLA antibodies. DSA were found in four (7%). One had transient Class I antibodies and normal cardiac function. The other three had persistent Class II antibodies (two subsequently required re-transplantation, the third had cardiac failure due to CAV). Non-DSA were found in 15 (25%), all with normal graft function and without rejection. There was no difference in function or CAV prevalence between those with non-DSA and those without antibodies. HLA DSA is uncommon in paediatric cardiac allograft recipients but, if persistent, suggests poorer prognosis. In our series, antibodies to HLA class II on donor tissue were associated with increased graft loss. Routine screening and regular testing are recommended.

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