Chromosome mapping of biological pathways by fluorescence-activated cell sorting and cell fusion: human interferon gamma receptor as a model system

Human chromosome 6 encodes both the interferon gamma receptor as well as the class I major histocompatability complex antigens, HLA-A, -B, and -C. However, the presence of chromosome 6 in somatic cell hybrids is insufficient to confer sensitivity to human interferon gamma (Hu-IFN-γ) as assayed by class I HLA induction; it is necessary for both human chromosomes 6 and 21 to reside in the hybrid to generate a response to Hu-IFN-γ. Treatment of such a hamster-human hybrid, Q72-18, with Hu-IFN-γ induces the class I HLA antigens. Q72-18 cells selected by fluorescence-activated cell sorting for the loss of class I HLA induction also lost human chromosome 21. Fusions of such cells to a hybrid that contains only human chromosome 21 reconstitutes HLA antigen induction by Hu-IFN-γ. Furthermore, fusions of hybrids containing a translocated human chromosome 6q and the HLA-B7 gene to a line containing only human chromosome 21 or a translocated 21q also reconstitutes HLA-B7 mRNA and antigen induction by Hu-IFN-γ. Thus the segregation of cells on the basis of a biological effect by fluorescence-activated cell sorting and reconstitution by hybrid fusion provides a strategy by which some biological pathways can be mapped at a chromosomal level.