Demonstration of activation of B lymphocytes in New Zealand black mice at birth by an immunoradiometric assay for murine IgM.

We have developed a highly specific and sensitive "two-site" immunoradiometric assay for murine IgM in which antigen bound to immobilized antibody reacts with affinity-purified radiolabeled antibody. We utilized the sensitivity of this assay to study the rate of IgM secretion in short-term cultures by spleen cells from the autoimmune strains, New Zealand Black (NZB) and New Zealand Black by New Zealand White F1 hybrid (BW), and from normal (C57BL/6, DBA/2, NZW) mice. The temperature dependence of IgM secretion in short-term cultures, its pentameric structure, and the similar viability of NZB and normal strain spleen cells indicate that active IgM synthesis is being measured. We observed that the splenic B lymphocytes of NZB and BW mice, in contrast to normal strains, produce IgM in vitro at birth. By 6 to 8 weeks of age NZB and BW spleen cells produce 40 times more IgM than spleen cells from normal strains of mice. The IgM produced in vitro by splenic lymphocytes from NZB and BW mice is not absorbed by synegeneic or allogeneic thymocytes or erythrocytes.

Antigenic analysis of the major structural protein of the Mason-Pfizer monkey virus.

The major internal protein, p27 (m.w. 27,000 daltons) of the Mason-Pfizer monkey virus (MPMV) was purified by gel filtration and ion-exchange chromatography and then used to develop a radioimmunoassay (RIA). This RIA was specific for MPMV because no immunologic cross-reactivity was observed between p27 of MPMV and 13 different RNA tumor viruses of mammalian and avian origin. However, the p27 of MPMV grown in three different primate cells exhibited identical antigenic cross-reactivity. In addition, significant levels of p27 were found only in MPMV-infected cells. These results indicate that synthesis of p27 is induced after virus infection and that p27 represents a viral-coded protein.

Characterization of mouse mammary tumor viruses from primary tumor cell cultures.I. Immunologic and structural studies.

Primary cell cultures of mammary tumors from Rill, GR, DD, BALB/cfC3H, and BALB/c mice were prepared by trypsin-EDTA dissociation of tumors. Cultures from these strains contained predominantly cells of epithelial morphology which formed three-dimensional domelike structures. Cultures from Rill, GR, DD, and BALB/cfC3H tumors produced extra-cellular type-B mouse mammary tumor virus(es) (MuMTV), either in the absence of detectable type-C virus or with less than 1% contamination with type-C virus. This was determined by radioimmunoassays for MuMTV and murine leukemia virus (MuLV) antigens. Only BALB/c cultures produced MuMTV with as much as 3% contaminating MuLV. High levels of MuMTV surface antigen were also found in soluble form in culture supernatants. Virus polypeptide analyses by electrophoresis on polyacrylamide gels showed that the Rill BALB/cfC3H, DD, and BALB/c viruses all contained polypeptides characteristic of MuMTV. Primary cultures of mammary tumor cells make available a source of purified MuMTV antigens, structural proteins, and nucleic acids for comparative studies of MuMTV from various mouse strains.