Human antibodies binding to the mouse mammary tumor virus: a nonspecific reaction?

Specific rabbit antisera and over 100 human sera were found to precipitate iodinated mouse mammary tumor virus (MTV). The specificity of these reactions was tested in competitive inhibition studies. Three classes of reaction could be distinguished. The Class 1 reaction was the most specific; it could be inhibited only by MTV and was observed exclusively with rabbit anti-MTV. The Class 2 reaction was apparently against mouse cell determinants; it could be inhibited not only by MTV but also by mouse lactating mammary gland and was characteristic of rabbit anti-mouse lactating mammary gland. The Class 3 reaction was the least specific; it could be inhibited not only by MTV and mouse lactating mammary gland but also by dog milk. All of the human sera tested exhibited Class 3 reactivities.