Biochemical evidence linking the G(IX) thymocyte surface antigen to the gp69/71 envelope glycoprotein of murine leukemia virus

The alloantigen GIX is found on the surface of thymocytes of some strains of mice (GIX⁺), where it is demonstrable by complement (C) dependent lysis (cytotoxicity assay) with (W/Fu x BN)F₁ anti W/Fu(C58NT)D (anti NTD) serum, and not on the thymocytes of other strains (GIX^-). Its expression in mice of the 129 strain, where its genetics has been studied in most detail, is controlled by 2 unlinked chromosomal loci. (Control of its expression in other GIX⁺ mouse strains may differ in detail from that of strain 129, and this is a subject of continuing study). An important feature of GIX antigen is its relation to leukemia virus and leukemogenesis. Thus, cells other than thymocytes, and from GIX^- as well as GIX⁺ mouse strains (and from rats), may express GIX antigen if they become productively infected with murine leukemia virus (MuLV). In the accompanying paper, Obata et al. give serological evidence that GIX antigen is a constituent of the gp69/71 glycoprotein component of the MuLV envelope, implying that the mendelian inheritance of GIX in certain mouse strains signifies the mendelian inheritance of a component of MuLV expressed selectively on cells following the T lymphocyte differentiative pathway. Reported here is a related study in which a molecule resembling gp69/71 was isolated from intact thymocytes of 129 mice by enzymatic radioiodination of the thymocyte surface, followed by release of this glycoprotein with the nonionic detergent Nonidet P 40 (NP 40) and precipitation with anti NTD serum; the product was then compared with envelope proteins isolated from purified MuLV. The authors' interpretation is that GIX antigen is carried by a glycoprotein with a mol wt of approximately 70,000 daltons which possesses other antigens identifying it as the gp69/71 glycoprotein component of MuLV.