413. Genetic diversity of the major histocompatibility complex and response to immunocontraceptives in the brushtail possum

Abstract

The brushtail possum (Trichosurus vulpecula) is a major invasive pest in New Zealand. One option for its control is the use of an immunocontraceptive vaccine, a method of fertility control that employs the immune system to attack reproductive cells or proteins. Initial trials of immunocontraceptive vaccines have shown individual variation in immune response. Concerns have been raised that the use of such a vaccine on wild populations could result in selection for possums that remain fertile because of low or no response, and subsequently negate the efficacy of the vaccine. Therefore, it is important to establish the basis of this variation. The major histocompatibility complex (MHC) is an important component of the immune system which influences the nature of immune responses. This study aimed to document genetic variation in MHC loci of New Zealand possums, and investigate whether there was a relationship between MHC haplotypes and individual immune responses to immunocontraceptive vaccines. We used known marsupial (possum, red-necked wallaby, tammar wallaby, opossum) MHC sequences to design PCR primers for possum MHC loci. The variability of these loci was screened in populations of possums from locations throughout New Zealand, and between individuals with known responses to immunocontraceptive vaccines. We identified 71 novel class I and class II MHC alleles and observed significant variation in allele identity and frequency between geographically separate possum populations in New Zealand. Comparisons of MHC haplotype and immunocontraceptive vaccine response showed that some of these alleles differ between high-responding and low-responding possums. The considerable variation we have found in the possum MHC, combined with differences in the occurrence of MHC genes at locations around New Zealand, provide a potential basis for the observed variability of individual possum's responses to immunocontraceptive vaccines.