Porcine class I major histocompatibility (MHC) genes have been introduced into the genome of C57BL/10 mice in order to study their in vivo patterns of expression and to analyze the ability of their products to function. One transgenic line which contains a classical class I MHC gene (PD1) expresses SLA antigen on its cell surface skin grafts from the B1O.PD1 transgenic are rejected by normal C57BL/10 mice, indicating that the foreign SLA antigen is recognized as a functional transplantation antigen Expression of PD1 parallels that observed in the swine, indicating that its expression is regulated. In vivo treatment of the transgenic with sigma/beta-interferon increases PD1 expression in a number of tissues. To further characterize regulatory DNA sequence elements responsible for tissue specific expression of class I gene, a series of 5' deletion mutants of PD1 was generated. DNA constructs containing the deletions mutants ligated to a reporter gene, CAT, were introduced into transgenic animals and assessed for their patterns of expression. Within 1.1 kb upstream of transcriptional initiation, negative and positive regulatory elements were identified, some of which function in a tissue specific fashion. In particular, a complex element consisting of an overlapping enhancer and silencer demonstrates marked tissue specificity. Transgenic lines have been generated containing a swine class I gene PD7, which is closely related to PD1. The two lines differ in the extent of non-coding 5' flanking sequence which has been introduced with the PD7 gene. Analysis of PD7 expression in the two lines has revealed the presence of tissue specific silencer associated with the gene. The difference in extent of 5' flanking sequences in the two constructs results not only in differential levels of antigen expression but different rates of graft rejection.
