Even after repeated immunizations with alpha(1-3)dextran (Dex) male (CBA/N x BALB/c)F1 mice fail to produce specific antibodies whereas nondefective female littermates express an idiotype-positive anti-Dex immune response. This failure of xid mice to express serum anti-Dex immunoglobulins is not only limited to immunization with the thymus-independent (TI-2) antigen Dex, since immunization with anti-idiotypic antibodies against Dex-specific idiotypes does not overcome this defect. When xid lymphocytes are cultured in the presence of mitogens, in vitro anti-Dex responses are markedly reduced. We show here that alpha(1-3)Dex-specific hybridomas can be established by fusion of splenic lymphocytes from xid mice to Sp2/0 myeloma cells. Therefore, these mice do carry the potential to generate B cells specific for Dex. All hybridoma antibodies were found to be of IgM isotype, bearing the lambda light chain typical for alpha(1-3)Dex-specific antibodies. Whereas monoclonal anti-Dex antibodies obtained from spleen cell hybridomas from female littermates showed variable idiotope patterns, hybridoma proteins from the immune-defective NBF1-xid mouse expressed only a limited pattern of Dex-specific idiotopes, suggesting that these hybridomas derived from a common precursor.
Immune cells transferred into nonirradiated animals of the same genotype face a barrier which severely affects their capacity to function in the host. We studied this phenomenon in allotype-congeneic animals. When anti-dextran immune cells of the responder strain (BALB/c-Igha) are injected into an allotype-congeneic host (BALB-Ighb) the grafted cells are suppressed to give an idiotype-positive response. This congeneic barrier of thymus-independent immune cells is lost in mice carrying an X-linked B cell defect: when idiotype-positive immune cells from responder (CBA/N X BALB/c)F1 mice are transplanted into congeneic nonresponder animals (CBA/N X BALB-Ighb)F1, female recipients are nonpermissive towards grafted cells whereas B cell-defective male littermates allow donor cells to develop an idiotype-positive anti-dextran response. These results show that the congeneic barrier towards dextran-immune cells is related to the maturation stage of B cells in the recipient. Since B cell-defective (CBA/N X BALB/c)F1 animals do not display an anti-idiotypic response in contrast to intact littermates and because CB16-KN mice are nonpermissive towards CB8-K lymphocytes, differing in VH genes only, we suggest that the "isogeneic barrier" depends on a mechanism recognizing VH structures.
Nude mice, congenitally lacking a thymus and immunologically deficient in their response to T-dependent antigens, can be restored in vivo and in vitro by the addition of syngeneic or allogeneic T cells (1, 2). Restored animals respond to sheep erythrocytes (SRBC) with good antibody titers, whereas control mice, without T cells, cannot. However, when nude mice are pretreated with antigen (SRBC) and then several days later restored with thymus-derived cells, they are unable to respond to a second administration of antigen (3, 4).It has been suggested that B cells are triggered to antibody production only if they receive two signals, whereas antigen stimulation alone without the relevant second signal would paralyze the B cell (5). On the other hand, induction of memory cells in nude or thymectomized animals has been demonstrated in several experiments (6-8).In the present paper we studied the capability of overtly unresponsive nu/nu cells, to give an in vitro response in the presence of a T-cell-replacing factor (TRF) 1 derived from congeneic thymus cells. With this experimental design uncontrolled effects of additional T cells are avoided.
Materials and MethodsAnimals. BALB/c-nu/nu mice were purchased through Bomholtgard, Ry, Denmark or derived from our own breeding stock (10th-12th backcross generation). BALB/c-lg b mice, 4-to 5-wk old, were used to produce activated T cells; mice 8-12-wk old were taken as a source of spleen cells for the production of a TRF.Immunization and Cell Transfer. BALB/c nu/nu mice were immunized with a single dose of 3-5 x 108 SRBC at the age of 6-8 wk. Congeneic thymus-derived cells were given to these mice at different times after the injection of antigen. At varying times after the first or second injection, spleen cells were harvested, washed in Eagle's medium, and transferred to in vitro cultures for incubation in the presence or absence of a TRF.Activated T Cells. Antigen-activated T cells were derived from the spleen of BALB/c-lg b mice which had been irradiated and injected with 5 x 10 ~ syngeneic thymocytes and 3 × 10 s SRBC 7 days before use.Cell Culture Conditions. Spleen cell cultures from nu/nu mice were prepared according to the method of Mishell and Dutton (9) and incubated in the presence of 2-mercaptoethanol (10). SRBC were used as antigen at a dose of 5 x 106 SRBC per 107 cells. After 4 days of in vitro incubation in the presence or absence of a TRF, four culture dishes of one group were pooled and the number of antibody-producing cells was determined in triplicate with a modified Jerne plaque technique.TRF. TRF was produced in BALB/c-lg b spleen cell cultures after stimulation by concanavalin * Supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsberereich 138 Biologische Grenzfl/ichen und Spezifit{it.
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