The present invention relates to the interactions between MHC Class I molecules and Co-expressed Proteins within the same cell (i.e., cis interaction). These interactions affect overt functional cellular processes by way of influencing protein trafficking and/or signal transduction. For example, in the nervous system, MHC Class I/Co-expressed Protein Interactions can have functional consequences affecting normal brain development, neuronal differentiation, synaptic plasticity and other physiological events. The polymorphic nature of the MHC Class I molecules imparts multiple differences among individuals with regard to the ability of an individual's MHC Class I molecules to interact with specific Co-expressed Proteins and affect cellular function--including the extent to which an individual's inherited MHC Class I haplotypes can affect that individual's specific development, susceptibility to developing diseases and/or their ability to respond to cellular loss, disruption or damage.