Endogenous retroviruses (ERVs) are remnants of ancient retroviral infections of the host germline transmitted vertically from generation to generation. It is hypothesized that some ERVs are used by the host as restriction factors to block the infection of pathogenic retroviruses. Indeed. some ERVs efficiently interfere with the replication of related exogenous retroviruses. https://www.footballmediaservices.com/product-category/air-acetylene-outfit/