Immunology of the mouse mammary tumor virus (MTV): neutralization of MTV by mouse antiserum.

years; antisera from rabbits, rats, and guinea pigs immunized with MTV-containing tissue extracts are capable of neutralizing the biologic activity of the virus (1, 2, 3, 6, 9). More recently, it has been demonstrated that MTV is also immunogenic in the mouse; antisera from immunized mice react with MTV antigen in immunodiffusion to produce a precipitate line specific for MTV (5, 11). The present communication reports that mouse antiserum is also capable of neutralizing the biologic activity of MTV. MTV antigen for immunization of the mice was prepared by centrifugation of MTV in a sucrose density gradient, as pre viously described (7, 8). The source of virus was milk obtained from BALB/cCrgl mice that had been fostered on DBA/2Crgl mice, and therefore were infected with the MTV carried by that strain. Each of five I"/BiCrgl adult female mice received an intraperitoneal injection of saline containing the MTV derived from 0.01 ml milk on Days 1, 4, 8, and 22. The mice were bled 2 weeks after the last injection, and their sera were pooled and frozen in a commercial refrigerator. The pooled serum contained antibodies against MTV, as measured by the development of the precipitate line specific for MTV, when it was tested in immunodiffusion against MTV antigen (5). Normal mouse serum for control purposes was obtained from normal adult BALB/c male mice. Serum from several donors was pooled and frozen until needed. Biologically active MTV for the neutralization experiment was prepared from an extract of BALB/cfC3HCrgl lactating mammary gland tissue by sedimentation in the ultracentrifuge, as previously described (3). The neutralization procedure was carried out in vitro at room temperature (3, 6). Equal amounts of undiluted mouse serum and saline, or saline alone, were combined in test tubes with the virus preparation so that 1 ml of solution contained MTV from 0.05 gm of lactating gland tissue. After 2 hours, 0.2-ml