[Immunological specificity and the kinetics of T-suppressor induction in the immunization of mice with allogeneic spleen]

A high dose immunization of mice with gamma-irradiated allogeneic spleen cells has been shown to induce, in a recipient spleen, specific suppressor T-cells, resistant to mitomycin C, which are capable of inhibiting DNA synthesis and, to a lesser degree, the generation of killer cells in the mixed lymphocyte culture (MLC). The maximum suppressor activity is reached on days 3-6 after immunization. Both reactions are blocked mostly in those stimulator cells which bear H-2 antigens used for immunization. In contrast, DNA synthesis is inhibited only slightly, if at all, when it is stimulated in MLC by third-party cells, even if these are added to the culture as a mixture with correspoding stimulators. Unlike X-irradiated allogeneic cells, the untreated ones induce a mixture of suppressors, T-cells and macrophages, with a considerable non-specific suppression. Untreated syngenic lymphoid cells induce less active non-specific suppressors with properties of macrophages.

[Immunologic specificity, nature and properties of suppressor cells induced in mixed lymphocyte cultures]

Suppressor cells are generated in allogeneic or syngeneic one-way mixed lymphocyte culture (MLC) for 1 to 5 days, the suppressor activity being tested by inhibition of proliferation of 10 to 100-fold number responders in the fresh allogeneic MLC. In both allogeneic and syngeneic MLC the suppressors are found to be neither B cells, nor macrophages, resistant to mitomycin C, and their precursors are shown to be cyclophosphamide sensitive. Their properties differ from those previously shown for T killers or T suppressors generated in the lymphocyte monoculture. The allogeneic suppressors are T cells that are heterogeneous in respect to radiosensitivity and specificity. Generation of the nonspecific T suppressors is reduced if human or bovine serum is added to the MLC medium instead of fetal calf serum. The syngeneic suppressors are heterogeneous as well and differ from the allogeneic ones by greater stability to the effect of anti-T bodies and irradiation, and by greater resistance of their precursors to hydrocortisone.

[Characteristics of T-Suppressors concentrated by elution from an allogeneic cell monolayer]

Quantitative enrichment of the immune lymphocyte fraction with H-2 antigen-specified suppressor cells was obtained by their elution from the relevant allogeneic monolayer of target cells. This was accompanied by 2-3-fold gain in the content of T lymphocytes and DNA synthetizing cells, as well as in the total (3)H-thymidine incorporation resulting from an increase in the percentage of medium and large lymphocytes in the population and also in the proportion of DNA synthesizing small and medium lymphocytes. Complete abolition of the suppressor effect by treatment with anti-Thy-1 and anti-T antibodies rather than with anti-B serum, and the resistance of this effect to carrageenan and carbonyl iron indicate the T cell nature of the eluted suppressor cells.

[Narrow specificity of T-suppressor receptors immune to H-2 complex antigens]

Specific d anti-b and b anti-a suppressor T cells induced by intravenous injection of mice with gamma-irradiated allogenic lymphoid cells, are not a homogenous population of cells as shown by their selective absorption on macrophage monolayers of various H-2 haplotypes. This is proved by separation of suppressor T cells to two subpopulations, at least, each of them being able to react with the products of only one (K or D) end of the H-2 complex. Moreover, the fine specificity study of d anti-b suppressor T cells enriched by elution from macrophage monolayers of different H-2 haplotypes, demonstrated these suppressors to represent a set of narrow-specific clones, each of them carried receptors reactive in a selective fashion with a particular determinant of the H-2 molecule irrespective of this linkage with other products of the H-2 complex. Two such clones reactive with H-2a and H-2f third-party antigens, respectively, were isolated by elution from the corresponding cell monolayers, each of them accounted for about 1.5% of the total d anti-b suppressor population. These data are discussed in the light of differences of suppressor T cells from other T cell subclasses and their resemblance to B cells with respect to the clonal structure and the receptor specificity.

[Induction of T-suppressor cells by immunization with allogenic spleen cells in the H-2 system of mice]

The nature of suppressor cells induced by immunization with the allogenic spleen cells and inhibiting the DNA synthesis activation in the mixed lymphocyte culture was studied. Suppressor cells are resistant to mitomycin C and carrageenan. They are not inactivated by the treatment with rabbit anti-B- and anti-Ig- as well as with mouse antibodies (anti-Mls serum) against B lymphocytes in the presence of complement but eliminated by rabbit anti-lymphocyte and anti-T globulins and by mouse anti-theta serum. These T suppressor cells are concentrated in the large lymphocyte fraction in the ficoll gradient. Their blocking of the DNA synthesis activation is evidently non-specific.

[Nature of the suppressor cells blocking the activation of DNA synthesis in mixed cultures of normal lymphocytes]

The nature of suppressor cells which are contained in lymphocyte suspension of mice immunized with allogeneic tumor cells and inhibit the DNA synthesis activation in mixed normal lymphocyte cultures has been studied. The suppressor cells are shown to be resistant to mitomycin C, X-irradiation and are not inactivated by the treatment of anti-O-serum or anti-Ig-serum in the presence of the complement. They adhere to the plastic and are inactivated by carrageenan in vitro. The macrophage nature of the suppressor cells is suggested.

[Effect of erythrocyte breakdown products on mast cells and erythropoietin formation]

Experiments were conducted on CBA mice and albino rats. A study was made of the effect of erythrocyte destruction products (EDP) on the content of hemopoietic colony-forming units (CFU), differentiation of stem cells and the erythropoietin production. It was shown that 3 or 4 EDP injections to normal mice or to lethally irradiated (1000 rad) mice after the transplantation of bone marrow cells caused no changes in the CFU level of stem cells differentiation. In case of a daily (for 3 days) administration of EDP to mice before the irradiation (1000 rad) and bone marrow transplantation there was observed an increase of the colonies count in the recipients' spleen on account of the erythroid colonies. EDP injection caused no changes in the erythropoietic activity of the blood serum. A possible role of erythrocyte destruction products in the mechanism of erythropoiesis autoregulation is discussed.

[Mechanism of action of benzene on hematopoiesis (a study of hematopoietic stem cells)]

A study was made of the effect of benzol on the colony-forming activity in the spleen and the bone marrow of mice in 4 different experimental variants. In benzol hypoplasia of hemopoiesis there was a decrease in the number of the CFU in the hemopoietic organs without any changes in the distribution of their cell types. Incubation of the cells of normal mouse bone marrow with benzol did not induce any decrease of the colony-forming efficiency. Administration of benzol to the lethally irradiated mice after the transplantation of normal bone marrow suspension led to a sharp decrease in the number of CFU with a preponderant depression of the granulocytic colony formation. These data afford to suppose the change in the properties of microenvironment of the hemopoietic stem cells in experimental benzol poisoning.