Activation of human B lymphocytes. XVII. Synergy between nonspecific and specific signals in the antigen-specific responses of human B cells

Autologous red blood cells potentiate antibody synthesis by unfractionated human mononuclear cell cultures

We have tried to determine the most favourable conditions for the in vitro induction of specific antibody (Ab) responses to tetanus toxoid (TT) and keyhole limpet haemocyanin (KLH). Human peripheral blood mononuclear cells (PBMNC) were obtained from normal volunteers and stimulated with PWM, TT, KLH, and mixtures of PWM and antigens in the presence or absence of autologous red blood cells (RBC) (1:50 ratio of PBMNC/RBC). The cultures were harvested on day 11; immunoglobulins were determined immunonephelometrically and Ab levels by ELISA with human antibodies used for calibration. While anti-TT responses were easy to induce with PBMNC from recently boosted individuals, the production of anti-TT from PBMNC obtained from non-recently boosted individuals was only possible when PBMNC were stimulated with TT and PWM in the presence of autologous RBC. Similarly, anti-KLH responses were easier to induce with PBMNC from an immune donor; maximal response was observed after stimulation with PWM + KLH in the presence of autologous RBC. Stimulation of primary anti-KLH responses with PBMNC from non-immune donors was only successful when the cells were stimulated with KLH + PWM in the presence of autologous RBC. The potentiation of human B-cell responses with autologous RBC can be abrogated by pretreatment of PBMNC with anti-CD2 antibodies and is associated with increased expression of IL-2 receptors and increased production of gamma interferon (IFN-gamma). However, addition of IFN-gamma in different doses and at different times to PWM-stimulated PBMNC cultures was not as effective as addition of RBC in enhancing the production of immunoglobulin and antibody.

Sheep red blood cells enhance T-lymphocyte proliferation

Small numbers of sheep red blood cells (SRBC) markedly augmented the proliferation of T lymphocytes activated by antigens or mitogens. This effect occurred with as few as one SRBC per T lymphocyte and with intact or osmotically lysed red cells. When increasing numbers of SRBC was added to T lymphocyte cultures stimulated with PHA or autologous cells, T lymphocyte proliferation peaked sharply at 10 to 50 SRBC per T cell. The SRBC did not influence resting T-lymphocytes. Rather, the effect occurred after T lymphocyte activation during cell division. There was a detectable increase in interleukin 2 (IL-2) receptor generation but not in IL-2 production by activated T lymphocytes cultured with SRBC versus medium alone. Finally, anti-T11 antibody could inhibit the SRBC enhancing effect on T-lymphocyte function, suggesting that an empty erythrocyte (E) receptor on the T lymphocyte was necessary for the SRBC action.

Antibody synthesis by bone marrow cells in vitro following primary and booster tetanus toxoid immunization in humans

Normal volunteers received either initial or booster immunization with tetanus toxoid. Bone marrow and peripheral blood mononuclear cells were obtained for up to 28 d after immunization and were analyzed for synthesis of total Ig and specific antibodies to tetanus toxoid. Cells were cultured in vitro for 3 or 7 d with or without pokeweed mitogen (PWM). Synthesis of IgG and IgM antibodies to tetanus (IgG-Tet and IgM-Tet) and total IgG and IgM was determined by radioimmunoassay. Four functional B cell subpopulations were detected in the bone marrow after booster tetanus immunization: (a) B cells that spontaneously synthesized IgG-Tet appeared on day 7 after immunization but were undetectable by day 21; (b) B cells that synthesized IgG-Tet after stimulation with PWM appeared after day 21 and persisted for greater than 1 mo; (c) B cells that synthesized IgM-Tet in the presence of PWM were detectable before and after immunization; and (d) B cells that spontaneously synthesized IgM-Tet appeared on day 7 and were undetectable by day 21. In contrast to the other three types of bone marrow B cells described, this fourth subpopulation of PWM-independent IgM-Tet-synthesizing B cells was not detected in the peripheral blood. After primary immunization, no spontaneous antibody-producing cells were detected in the blood or bone marrow, although there was a small rise in IgM-Tet in two of three subjects. In the bone marrow, only IgM-Tet PWM-inducible cells were seen, although mitogen-responsive IgM and IgG-Tet cells were detected in the circulation. The IgM-Tet PWM-reactive cells were present even before primary antigen exposure and appear to represent the initial B cells involved in the antibody response. These data indicate that there are specific times after immunization when different functional classes of anti-Tet-synthesizing B cells and memory B cells appear in human bone marrow. Knowledge of these data may be important in developing a strategy for the transfer of immune memory from donors to recipients in the setting of bone marrow transplantation.