Olof Sjöberg

Selective induction of DNA synthesis in T and B lymphocytes

Abstract The ability of concanavalin A (Con A) and a lipopolysaccharide from E. coli bacteria (LPS) to induce DNA synthesis in various types of mouse lymphocytes cultivated in vitro was investigated. The results demonstrate that Con A is selectively active on T cells, being capable of activating DNA synthesis in thymocytes, cortisone-treated thymocytes, peripheral “educated” T cells, spleen cells and to a smaller degree bone marrow cells. When T cells are removed from spleen cell suspensions by treating them with antitheta serum, the effect of Con A is markedly reduced. Spleen cells from thymectomized and lethally irradiated mice repopulated with antitheta serum treated bone marrow (T × B mice) or spleen cells from congenitally athymic (nude) mice do not respond to Con A. Cortisone-treated thymocytes and spleen cells responded equally well to Con A; whereas untreated thymocytes respond 10 to 20 times less, suggesting that the cortisone-resistant thymocytes are the responsive cells both in the thymus and in the spleen. Pure T cells exhibited a very narrow dose response profile to Con A, 5 μg being optimal and 1 or 10 μg giving a small, or no, response. Contrarywise, a mixed T and B cell population, such as the spleen, showed a broad dose response profile to Con A. It is suggested that Con A-activated T cells can influence B cells to respond to Con A; whereas B cells by themselves cannot be activated by Con A. LPS cannot activate thymocytes, cortisone-treated thymocytes, or educated peripheral T cells, but stimulates DNA synthesis to an equal degree in normal spleen cells, antitheta-treated spleen cells, spleen cells from T × B or nude mice and normal bone marrow cells. LPS can induce DNA synthesis in spleen cells from animals tolerant to LPS to the same degree as in normal spleen cells. Another thymus-independent antigen (PVP) cannot activate DNA synthesis in normal spleen cells, suggesting that LPS exerts a non-specific stimulatory effect on B cells.

Mitogens as probes for immunocyte activation and cellular cooperation.

2. Proliferative responses to mitogens 2.1 Selective effects of mitogens on T and B lymphocytes 2.2 Activation of B cells by Con A 2.2.1 Evidence for a soluble T cell factor 2.2.2 Support for the local concentration hypothesis 2.3 Cap formation does not correlate with lymphocyte activation 2.4 High dose unresponsiveness to Con A is reversible 2.5 Quantitation of the number of activating mitogen molecules 2.6 A model for mitogen-induced lymphocyte stimulation

Lipopolysaccharides can convert heterologous red cells into thymus- -independent antigens.

Abstract Heterologous red cells coated with lipopolysaccharides (LPS) from E. coli O127 bacteria induced a normal immune response to the red cell antigen in thymectomized, lethally irradiated, and bone marrow repopulated mice (T × B mice); whereas uncoated red cells only stimulated a weak response. Lipopolysaccharides had to be present on the red cells to convert them to thymus-independent antigens. T × B mice pretreated with large doses of LPS, in order to induce immunological tolerance, responded to LPS-coated red cells better than nonthymectomized mice to red cells alone. Passive transfer of antibody to LPS suppressed the response to red cells in T × B mice injected with LPS-coated red cells. Since LPS has been found to be a mitogen for bone marrow-derived (B) cells, it is suggested that this property is responsible for the ability of LPS to substitute for thymus-derived (T) cells. Consequently, the signal from T to B cells may be nonspecific.

Effect of antigenic competition on antigen-sensitive cells and on adoptively transferred immunocompetent cells

Abstract Antigenic competition between the primary immune response to noncrossreacting sheep and horse red blood cells was observed only when the two antigens were spaced in time. A secondary immune response to one antigen markedly suppressed the primary response to the other. The number of antigen-sensitive cell was the same in normal mice and in animals expressing antigenic competition, as demonstrated by a transfer system. Adoptive transfer of normal or sensitized spleen cells mixed with antigen into irradiated recipients exhibiting antigenic competition resulted in marked suppression of cellular antibody production as compared to the response in previously nonimmunized recipients.

Antigen‐Binding Cells in Immune and Tolerant Animals

Cellular cooperation between different types of lymphoid cells operates in the induction of humoral and possibly also of cellular immunity. According to recently acquired knowledge it is possible to explain the hapten-carrier effect (Ovary & Benacerraf 1963) as reflecting a similar cellular cooperative activity (Mitchison 1969, 1971b, c, Rajewsky 1969). A synergistic effect can be obtained between thymus-derived lymphoid cells (T) and bursa-equivalent or non-thymus-derived lymphoid cells (B) in the induction of humoral immunity against certain antigens (see Transplant. Rev. 1, 1969, for ref.). It seems a likely assumption that T cells react with antigen via specific antigen-binding receptors present on the cell surface and synthesized by the T cells (Greaves & Moller 1970, Basten et al. 1971, Roelants & Askonas 1971). The antigen-specific T cells present the antigen to the precursors of the antibody-forming cells, which are B cells (Mitchell & Miller 1968) and also carry specific receptors. The interaction between T and B cells would increase the efficiency of binding of the antigen to the B cell receptor, probably by allowing multiple bond formation and thereby increasing the likelihood of stimulating the B cell precursors to undergo proliferation and differentiation into mature secreting cells. In the response to hapten-protein conjugates it has been shown that T cells react with the carrier molecule, since an adoptive humoral response to the hapten is abolished if the carrier-specific cells are treated with anti-6> serum (Raff 1970), which selectively kills T lymphoid cells (Raff 1969).

Antibody-induced lymphocyte-mediated cytotoxicity in sarcoidosis patients and healthy controls

Abstract The cytotoxic activity in antibody-induced cell-mediated cytotoxicity of human lymphocytes from sarcoidosis patients and from healthy blood donors was studied using YAC (H-2 a ) Moloney virus-induced ascites leukemia cells from mice as target cells and a rabbit antimouse antiserum. Human lymphocytes were prepared from blood by separation on a Ficoll-Isopaque gradient followed by treatment with iron powder to remove phagocytic cells. The cytotoxic system had high sensitivity; 1–2 × 10 6 lymphocytes were able to kill 10 5 YAC cells completely at an antiserum dilution of 10 −4 . Even as few as 25 × 10 3 lymphocytes killed 20% of the target cells. Adherent cells showed no cytotoxic activity in this system. No difference was found in the cytotoxic activity of lymphocytes from sarcoidosis patients and from healthy blood donors.

Presence of Antigen Binding Cells in Mice Tolerant to E. Coli Polysaccharide

The immune response involves the appearance of antibody secreting cells (plaque forming cells, PFC) (l) as well as antigen binding cells (rosette-forming cells, RFC) (2). Howard et al. (3) have reported the presence of RFC in animals, which were tolerant to pneumococcal polysaccharide, as Judged by the absence of a detectable serum antibody response. They suggested that antibody forming cells existed but that the antibodies produced were neutralized by excess antigen in the serum. To study if this hypothesis was true for another polysaccharide the cellular basis for tolerance towards polysaccharide of E. coli origin was examined in this study.