Factors interfering with cellular immunological responses to the murine mammary tumor virus in tumor-bearing mice

Abstract

T-cell-enriched spleen cell fractions from BALB/c mice bearing virally induced mammary tumors become unresponsive with progressive tumor growth in the lymphocyte blastogenesis test, using purified mammary tumor virus (MTV) as an antigen. Reactivity can be restored by mild trypsinization or extensive washing of the cells. When reactive cells from mice immunized with MTV were incubated with the wash fluid of the initially unresponsive cells, MTV-specific blastogenesis was inhibited. Washings of normal cells had no such effect. Leukocytes from tumor-bearing mice also become unresponsive t o MTV in the leukocyte adherence inhibition (LAI) assay. Trypsinization o r extensive washing does not restore reactivky. However, such treatment of reactive cells from immunized animals abolishes a positive reaction i n the LA1 assay, using MTV as an antigen. The washings of spleen cells from tumor-bearing mice inhibit the reactivity of leukocytes from immunized animals. Sera from these mice could block the reaction i n both cellular immunological tests. The inhibiting factors appeared early after the onset of tumor growth. By means of the Sepharose bead immunofluorescence assay it was established that wash fluid and sera with blocking activity contain MTV antigens as well as anti-MTV antibodies.