SUMMARY

Chicken sera may contain components hat immunologically crossreact with avian retroviral glycoprotein. Sera from chickens carrying the endogenous viral loci ev3 and ev6 contain glycoproteins with molecular weights of approx. 85 000, which on the basis of tryptic peptide analysis are related toexogenous viral glycoprotein. Such endogenous viral glycoproteins are present in a free form, lacking disulphide-bonded gp35. Endogenous retroviruses have been detected in a large number of animal species and have been particularly well studied in the domestic hicken, Gallus gallus, where some 20 different loci (ev loci) have been defined (Astrin, 1978; Astrin et al., 1980; Rovigatti & Astrin, 1983; Humphries et al.,!984). Individual chickens vary in the numbers and combinations of endogenous viruses integrated in their genomes (Hughes et al., 1981) and it has been possible to establish which ev loci are responsible for particular phenotypes ofexpression. For example, the presence of endogenous viral glycoproteins i fibroblasts, previously determined in the 'chicken helper factor (chf) assay ' (Hanafusa et al., 1973), results from expression of the ev loci 3, 6 or 9 (Baker et al., 1981; Rovigatti & Astrin, 1983). In previous studies, using immunological methods, we demonstrated that material immunologically crossreacting with viral glycoprotein was present in the sera of certain uninfected chickens (Bosch et al., 1978, 1983). In the present paper we have characterized the crossreacting antigen in chicken serum in order to establish that it is truly endogenous viral glycoprotein and to determine its molecular nature. Sera from chickens with the following genotypes were employed: ev 1, 2, ev 1, 3, and ev 1, 6 (referred to as ev 2, ev 3 and ev 6 sera). In addition, a serum from a chicken lacking ev loci (Astrin et al., 1979) was employed (ev-). The sera were generously supplied by Dr D. L. Ewert, Wista