Radioimmunoassay for the envelope glycoprotein of subgroup E avian leukosis-sarcoma viruses.

In the absence of infectious subgroup E avian leukosis-sarcoma (ALS) viruses, some chicken embryo cells contain in their cell membrane the envelope glycoprotein of subgroup E viruses (gpE) (Hanafusa et al. 1973). The partial expression of subgroup E virus was first recognized as chick-cell-associated helper factor (chfl, which provided the helper function for the envelope-defective Bryan high-titer strain of Rous sarcoma virus (BH-RSV) (Hanafusa et al., 1970a; Weiss and Payne, 1971). Thus, chf acts like a helper virus by determining envelope-antigen specificities such as host range, interference patterns, and neutralizability by antisera.