E ndogenous retroviral sequences (ERSs) belong to the larger family of retrotransposable elements that make up as much as 5-10% of the eukaryotic genome 1. They are a major factor in the shaping and reorganization of the genome 1. ERSs may have evolved from eukaryotic genomes and then become extracellular retroviruses 2, or they may have originated from exogenous retroviruses that integrated into the genome and became trapped owing to mutations of essential genes 1. Human ERSs have generally been found to be defective provi? uses. They represent a large reservoir of viral genes that may be activated by mutations caused by radiation or chemicals, or recombination with exogenous retroviruses. While exogenous retroviruses are infectious, with a replication cycle that requires integration of proviral DNA into host cell DNA, ERSs are transmitted genetically in a classical mendelian fashion through the germ line as proviral DNA. The human genome contains a complex variety of ERSs. While some ERSs are represented in a single copy per haploid genome, others are highly repetitive and occur at a frequency of up to 1000 copies per haploid genome 3.

Autoimmune diseases are characterized by the presence of circulating antibodies to self-antigens (autoantibodies) and of autoreactire T cells 4. Deposition of autoantibodies and immune complexes comprising autoantibodies and selfantigens is accompanied by tissue destruction. The cause of autoimmune diseases is not known 4, but a possible retroviral etiology was initially proposed based on the discovery of the deposition