In this project we will investigate and characterize MHC DQB polymorphism in bank voles (Myodes glareolus) in relation to multiple infections. Genes of the major compatiblity complex (MHC) are involved in the adaptive immune system and are the most variable genes in the vertebrate genome. Frequencies of given MHC alleles may increase or decrease in natural host populations due to processes of natural selection and/or random drift. Little is yet known about selective signals in the polymorphic gene region DQB and the project will focus on these regions. MHC DQB genes will be characterized and the effect of different MHC haplotypes on a range of natural infections will be investigated to understand how MHC varieties are selected for and against in natural populations depending on present and past selection from parasites/pathogens.