Antigenic relationship between medullary thymocytes and a subpopulation of peripheral T cells in the rat: description of a masked antigen

The effect of steroids on the circulating lymphocyte population--VI. Studies of the thoracic duct T- and B-lymphocyte populations after neonatal thymectomy and prednisolone treatment. An immunofluorescence study in the rat

The corticosteroid effect on circulating lymphocytes in a steroid-sensitive species (rat) was studied by immunofluorescence. Both normal and neonatally thymectomized animals were injected with a high dose of prednisolone. T- and B-lymphocytes as well as T-lymphocyte subsets were analyzed in thoracic duct lymph during the involution phase (3 h after injection) and the restitution phase (17 h after injection) using conventional and monoclonal antisera. Neonatal thymectomy significantly reduced the number of circulating T-helper and T-non helper cells. In the involution phase, after a corticosteroid injection, there was a 64% reduction of lymph cell content in normal rats, affecting both T- and B-lymphocytes. Thymectomized animals showed an even more pronounced disappearance of cells. Counted in percentage, more B- than T-lymphocytes disappeared from the circulation. The T-non helper cells disappeared to a greater extent than the T-helper cells did. Cells with Ia-antigen showed about the same values as the B-lymphocytes. During the restitution phase all cells types were restored to normal levels. It seems that a high prednisolone dose has a more pronounced effect on the circulation of B- than of T-lymphocytes, and the T-non helper cells are probably more sensitive than the T-helper subpopulation. These data support the hypothesis that a major corticosteroid effect is a trapping and redistribution of circulating lymphocytes, more pronounced for certain cell types.

Induction of terminal deoxynucleotidyl transferase and Lyt antigens with thymosin: identification of multiple subsets of prothymocytes in mouse bone marrow and spleen

Thymosin (fraction 5 and synthetic alpha 1 peptide) induced prothymocytes in mouse bone marrow and spleen to express terminal deoxynucleotidyl transferase (TdT; DNA nucleotidylexotransferase; nucleosidetriphosphate:DNA deoxynucleotidylexotransferase, EC 2.7.7.31) or Lyt-1+, 2+, 3+ alloantigens (or both) after brief incubation in vitro. Three antigenic phenotypes were generated: (i) TdT+ Lyt+, (ii) TdT- Lyt+, and (iii) TdT+ Lyt-. The TdT+ Lyt+ phenotype was expressed by 80% of prothymocytes in bone marrow and 30% of prothymocytes in spleen from normal mice. The TdT- Lyt+ phenotype was expressed by 81% of prothymocytes in bone marrow from athymic mice. More than 80% of TdT+ bone marrow cells from normal and athymic mice expressed Lyt antigens after thymosin treatment. We interpret these observations as suggesting that (i) most TdT+ hemopoietic cells in normal and athymic mice are thymocyte progenitors; (ii) two independent lineages of prothymocytes exist, one that expresses TdT and another that does not, (iii) commitment of prothymocytes to the TdT+ cell pathway is partially regulated by a thymic feedback mechanism; and (iv) the bone marrow preferentially produces TdT+ prothymocytes, whereas the spleen may serve as a repository for TdT- prothymocytes. A model of T-cell development is presented in which the thymus functions as a compound organ to process TdT+ and TdT- thymocytes progenitors and to generate two lines of T cells.

Varying expressions of lectin receptors within embryonic cell layers of murine cerebral cortex

The ability of prenatal cerebral tissue to bind different lectins was analyzed using cryostat sections of mouse brains. It was shown that the immature cells within the embryonic cell layers possess receptors for different lectins in varying amounts. Of all lectins tested, only PNL, RCL and LPL were bound on the outer cell membranes to a considerable degree. Although the labeling patterns of PNL and RCL are similar, the latter is additionally well detectable on the wall of cerebral blood vessels. Cells of the ventricular layer are moderately labeled by PNL, which recognizes beta-D-galactosyl (1-3)-N-acetyl-D-galactosamine, but heavily labeled by LPL which binds to terminal sialic acid residues. Cells of the intermediate layer, on the other hand, are heavily stained PNL and only faintly by LPL. Hence it is suggested that the process of migration might be correlated to the removal of terminal sialic acid moieties from cell surface glycoconjugates, resulting in an exposure of the penultimate galactosyl residues.

Bone marrow transplantation into recipients sensitized against donor-type T cells

Immunization of prospective bone marrow recipients with thymocytes of the marrow donor strain prevented subsequent hemopoietic engraftment of the marrow. Immunization with thymocytes of a third party strain sharing the marrow donor's theta alloantigen but not his histocompatibility antigens permitted chimaerism and suppressed GVH in mice. Bone marrow of rat strains of the Th-1.1 group did not take in mice sensitized against mouse Th-1.1 thymocytes. This observation lead to the conclusion that hemopoietic stem cells of rats but not of mice express an early thymic and even prethymic antigen. This antigen is not restricted to the Th-1.1 specificity: rabbit anti-rat thymocyte globulin absorbed in a way which removed stem cell toxicity from a rabbit anti-mouse thymocyte globulin prevented hemopoietic engraftment when incubated with rat bone marrow before transfer to irradiated mice. Serologically this antiserum reacted with thymocytes as well as lymphocytes in the rat bone marrow but less with lymph node cells. An antiserum against rat lymph node cells was rendered T cell specific by absorption. It defined a postthymic T antigen lacking on stem cells, bone marrow lymphocytes and thymus. It labeled lymphocytes in the interfollicular T dependent area of lymph nodes by an immunohistochemical method. T cells in rats were thus found to express a prethymic and/or a postthymic antigen. Implications of theta alloantigens for the suppression of GVH in polytransfused bone marrow grafted patients are discussed.

Detection and partial characterization of a new murine T-lineage antigen: evidence for its enzymatic modulation

A molecule with an apparent molecular weight of 21,000 daltons was found to be a predominating differentiation antigen of peripheral rat T lymphocytes. This antigen is also expressed on the cell surface of thymus lymphocytes though partially in masked form. The observation that these determinants could be unmasked by neuraminidase treatment in vitro suggests that enzymatic processes may play an important role in antigenic transformation along the differentiation pathway of T axis lymphocytes. Since this structure was found to be displayed also by peritoneal exudate macrophages, it is referred to as T lymphocyte-macrophage antigen. The finding that an identical antigen could be identified in the mouse suggests its more common biological significance.

The pattern of lymphocytes in the thymus and spleen after labeling with 3H-thymidine and 3H-deoxycytidine

Adult male untreated mice (NMRI) were investigated after radioactive labeling with 3H-thymidine and 3H-deoxycytidine to find out whether the lymphocytes in the cortex and medulla of the thymus as well as in the perifollicular and periarteriolar regions of the spleen show a labeling pattern which allows a classification into T- and B-lymphocytes. The percentages of radioactively labeled small lymphocytes and their mean grain counts were determined. The percentages of radioactively labeled small lymphocytes after 3H-TdR and 3H-CdR showed no significant differences in both splenic zones. The grain counts over the lymphocyte nuclei in the periarteriolar zone showed lower values after 3H-TdR than after 3H-CdR. The lymphocytes in the perifollicular zone were strongly labeled with 3H-TdR and weakly labeled with 3H-CdR. In the thymus medulla, lymphocytes were weakly labeled with 3H-thymidine and strongly labeled with 3H-CdR. In the cortex no significant differences were observed. 75 to 80% of the small lymphocytes in the peripheral blood were weakly and 20-25% strongly labeled after 3H-TdR. Therefore there are similarities in the radioactive labeling pattern of thymic medulla lymphocytes and that of small lymphocytes of the periarteriolar zone of the spleen by both DNA precursors. The small lymphocytes in the peripheral T-dependent tissue zones, for example in the spleen, as well as in the mixed lymphocyte population of the peripheral blood can be differentiated from the B-lymphocytes through the difference in the amount of incorporation of 3H-thymidine and 3H-deoxycytidine.

Thymocyte subpopulations in young and adult mice. II. Study of steroid-resistant populations by means of a specific heteroantiserum

Mouse steroid-resistant (Sr) cells of the thymus have been studied by means of a specific heteroantiserum. This antiserum was obtained in the rabbit after immunization with Sr thymocytes followed by absorption with high density cells isolated on a Ficoll density gradient shown to include a majority of steroid-sensitive (Ss) cells. Antigens defined by this antiserum were found on Sr thymocytes and on a significant portion of spleen and lymph node cells, but not on Ss cortical thymocytes. Cells sensitive to this antiserum appear early in the thymus (by day 15 of gestation) at the same time as Ss cells. These results suggest (a) the existence of an autonomous Sr cell line, with its own antigenic markers appearing early in ontogeny (at the same time as Ss cells), and showing wide heterogeneity in density, possibly linked to variable degrees in maturation, and (b) the medullary origin or some peripheral lymphocytes in lymph node and spleen cells that share antigenic markers with Sr thymocytes.

Differentiation antigens of the lymphocyte cell surface

Many alloantigens and xenoantigens of lymphocytes are not found generally on other tissues, and this suggests that much of the lymphocyte cell surface is differentiated in comparison with other cell membranes. These differentiation antigens are probably molecules that mediate lymphocyte-specific functions, and are also of interest in that they provide markers for different lymphoid cell types and may be important as target antigens for immunosuppressive anti-(lymphocyte) sera. The purification of differentiation antigens will be important in allowing their molecular properties to be discovered, and will also lead to the production of strong, specific antisera that can be used in functional studies. Radioimmunoassays have been developed for the analysis of anti-(lymphocyte) sera, and these assays provide advantages in purification studies over other techniques. The features of these assays are discussed, and studies of differentiation antigens of rat lymphocytes are described. These include the purification and characterization of the rat Thy-1 antigen, and preliminary studies on two other rat lymphocyte differentiation antigens.