Expression of the major group‐specific antigen (GS‐A) of avian type‐C viruses in normal chicken cells and tissues

The major group‐specific antigen (gs‐a) of avian type‐C viruses was detected by radioimmunoassay in all tissue samples and cultured cells from leukosts‐free chickens. Visceral tissues of individual embryos contained 7–36 ng antigen per mg protein. The mean values in adult tissues were 2–5 times lower than those of the embryos, except for spleen which gave exceedingly high values of about 50 ng per mg protein. The identity of the endogeneous gs‐a with viral gs‐a was established by several criteria. The gs‐a levels of tissues and cells producing avian type‐C viruses were 100–1,000 times higher. In such cells up to 1% of cellular protein can be gs‐a. Differences in expression of gs‐a and other malignancy‐associated proteins in normal tissues may prove useful indicators of loosened gene regulation as an initial step towards malignancy.