The effect of dietary restriction on the expression of retroviral envelope glycoprotein, gp70, and the formation of gp70-anti gp70 immune complexes was investigated in lupus-prone NZB x NZW F1 hybrid mice. Restricting total calorie intake from the usual 20 to only 10 calories per day after weaning markedly reduced serum levels of both free and antibody-complexed gp70, prevented renal disease, and increased the life spans of these mice. The reduction in serum gp70 was evident after only 2 wk of feeding these animals the low-calorie diet, and the concentration remained virtually unchanged throughout the course of 10 mon experimentation. However, serum concentrations of the major structural protein, p30, of endogenous retroviruses were not altered by restricting calories. Amounts of the serum glycoprotein, haptoglobin, decreased parallel to those of gp70 but amounts of albumin did not. These results suggest that the expression of gp70 in serum is controlled independently of the production of complete viral particles, and regulated by a mechanism similar to that for other serum glycoproteins, such as haptoglobin.

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