Abstract
The third component of complement (C3) is synthesized and secreted by cultured human primary fibroblasts. A monoclonal antibody having specificity for an antigenic determinant carried by human but not mouse C3 was used to study the continued expression of human C3 in three panels of independently derived human-mouse somatic cell hybrids. Expression of the human product was shown to segregate with human chromosome 19 and with no other chromosome or group of chromosomes. A unique-sequence human genomic C3 DNA clone was isolated and used as a probe in DNA hybridization experiments with DNA prepared from appropriate human-mouse somatic cell hybrids to confirm assignment of the human C3 gene to chromosome 19.