Age- and tumor-correlated changes in functional antibody responses to MTV in neonatally infected mice.

BALB/cfC3H female mice (neonatally infected with MTV) possess several different specific antibody activities measured functionally by reactivity with MTV-associated antigens expressed on the surface of isologous MTV-induced mammary tumor target cells. All females when young develop serum antibody which can block specific T-cell cytotoxic activity of BALB/cfC3H spleen cells; this activity remains detectable throughout life. In addition, recruiting antibody is found in the post-weaning stage. This recruiting activity is apparently directed against the same antigenicity as the blocking activity; it can be detected only rarely in whole serum but is revealed in the 19S fraction when the competing blocking antibodies are sequestered into the 7S fraction. In mid-adult life, 19S recruiting activity is found in only a few of the females; the incidence increases as the females age, and it occurs earlier in those females which subsequently develop mammary tumors. A third antibody activity of serum is blocking factor directed against different MTV-associated tumor-cell-surface antigenicity; this blocks the antibody-dependent cell-mediated cytotoxicity characteristic of spleen cells from BALB/c females horizontally exposed to MTV-associated antigenicity. This blocking activity of serum is not found in young females, and in the older females it is more frequent in those which develop mammary tumors.