Suppressor T cells in thymus-reconstituted nude mice: regulation of mitogen-induced transformation

A population of glass-wool-adherent splenic cells which could suppress the response of other spleen cell populations to T-cell mitogens was isolated from thymus-reconstituted nude mice. Such adherent cells were characterized as sensitive to anti-Thy 1.2 and complement treatment. Glass-wool-adherent cells from athymic mice do not have suppressor activity to self or normal littermate NAC; however, these mice possess precursor suppressor cells as demonstrated by isolation of glass-wool-adherent T regulatory cells in thymus-grafted nude mice. Such cells are generated in either freshly obtained or in vitro cultured thymus. Evidence for suppressor T cells of host genotype was supported by their sensitivity to host-specific anti-Thy serum treatment as well as their generation in alymphoid thymus grafts. Prior anti-Thy 1.2 treatment of GAC partially removed the suppressor activity: however, macrophages and B lymphocytes were shown not to be secondary regulatory cells or suppressor mediators, thus mature T lymphocytes with low amounts of Thy 1.2 antigen may be responsible for this residual suppression. Further characterization of GAC indicates that active cell growth is required for their regulatory function, as irradiation removed the suppressor activity. This report provides evidence for the presence of a T-lymphocyte subpopulation which has a regulatory function and requires a thymus in the generation of these cells.     

The restoration of the T-lymphoid system of nude mice: lower efficiency of nonlymphoid, epithelial thymus grafts.

The T-cell deficiency of nude mice is due to an abnormal differentiation of the thymus epithelium; it can be persistently corrected by grafting a neonatal thymus. However, grafted adult thymuses or epithelial thymuses are not repopulated by large numbers of host-derived lymphocytes, as is the case when a whole neonatal thymus is grafted. Furthermore, the repopulation of the spleen and lymph nodes by T cells is less pronounced than after whole neonatal thymus transplantation, and the restoration of the reactivity to T-cell mitogens is irregular. Therefore, the integrity and the age of the thymus graft are important for a good restoration of the T-lymphoid system of congenitally athymic animals.     

Increased number of Leu-2-bearing non-T cells with natural killer activity in chimpanzees

Peripheral blood lymphocytes from adult and adolescent chimpanzees, as well as adult humans, were studied for phenotypic surface markers by flow cytometry. Lymphocytes from chimpanzees were found to have increased numbers of Leu-1-, Leu-2+ cells as compared to humans. These cells, following preparative electronic cell sorting, were shown to possess natural killer function. Further analysis of this subpopulation indicated that they lacked responsiveness to a number of T-cell mitogens. The differences in lymphocyte subpopulations between chimpanzees and humans can almost be totally accounted for by the Leu-1-, Leu-2+ cells. Phylogenetic disparity between these two species may also be found within this population.     

Differential suppressive effects of antiserum to thymus ribosomal fraction on mitogen responsiveness of thymus cells

The effect of antiserum to thymus ribosomal fraction (ATRS) on the responsiveness of thymus cells to mitogens concanavalin A (Con A) and phytohemagglutinin (PHA) was investigated. ATRS preferentially suppressed the responsiveness of thymus cells to Con A whereas their PHA responsiveness remained unchanged. In contrast, thymus cells from mice treated with a single injection of cortisone acetate showed significant increases in thymidine uptake when stimulated by both PHA and Con A.     

Comparative study of the T- and B-cell immunity systems in human and animal embryogenesis

Data are presented on the spleen and thymus structure, time of appearance of the lymphocytes and their heterogeneity in the liver, thymus, spleen, lymph nodes and blood of human foetuses with hemochorial placenta (3 to 34 weeks) and of the minipigs foetuses with epitheliochorial placenta (32 to 95 days). In both foetuses the first T- and B-lymphocytes are found in liver, T-lymphocytes are then found in thymus and later in spleen and lymph nodes whereas B-lymphocytes are found, after liver, in spleen. Kinetics of T- and B-lymphocytes during embryogenesis is described. Reaction of the minipig lymphocytes to mitogens was demonstrated.     

Immunosuppressive antilymphocyte serum: IV. Characterization of a T-cell-specific antibody that shifts T-lymphocyte subpopulations in vivo

We have characterized a biologically active antibody present in immunosuppressive but not nonimmunosuppressive antilymphocyte serum. This antibody when administered to rats induced a dose-dependent fall in the numbers of one subpopulation of T lymphocytes while leaving a second subpopulation relatively untouched. When absorption studies were performed, the active antibody was shown to be T-cell specific and could be absorbed preferentially by a subpopulation of thymus lymphocytes which were steroid resistant. The data revealed that the relevant antigen was found in highest concentration on a minority of thymus cells.     

The effect of different Yersinia pestis antigens on the cellular link in immunity

Immunization with live plague vaccine has been shown to give no protection to thymectomized mice from subcutaneous challenge with Y. pestis virulent strain. Under the action of the vaccine or individual Y. pestis antigens (fraction I) the functional and morphological activation of thymocytes and macrophages is observed, more pronounced in C57BL/6 mice and less pronounced in CBA mice. Y. pestis antigenic preparations (fractions I and II, pesticin) act as T-cell mitogens and are thus capable of inducing the in vitro proliferation of thymocytes. At the same time the in vivo action of fraction II induces a decrease in the level of lymphocytes in the peripheral blood of mice and the destruction of lymphocytes in their thymus and spleen.     

Lymphocyte reaction in schizophrenia patients to the phytomitogens, concanavalin and phytohemagglutinin]

The capability of the schizophrenic patients' lymphocytes and lymphocytes of healthy persons to respond to the stimulating action of T-mutagens -- concanavalin A and PHA -- was studied. The T-cell count was determined by the method of rosette formation; the influence of adhesive cells on the lymphocyte response to mitogens was ascertained. The response to both the mitogens in the patients' lymphocyte cultures was reduced as compared to control, and the T-cell count failed to differ from the normal. The removal of adhesive lymphocytes results in the disappearance of differences between the response of the patients' lymphocytes and normal lymphocytes to both the mitogens.     

Asynchronous depression of responses to T- and B-cell mitogens during acute infection with cytomegalovirus in the guinea pig

The nonspecific functional capacity of spleen cells, taken from female guinea pigs with primary acute cytomegalovirus (CMV) infection, was assessed using lipopolysaccharide (LPS), a B-cell mitogen, and concanavalin A (Con A), a T-cell mitogen. Proliferative responses to the two mitogens were found to be significantly depressed in animals inoculated with CMV as compared to control animals. The defect in Con A responsiveness occurred earlier during the course of the infection than the defect in LPS responses. Although responses to the mitogens were depressed at the time of peak virus activity in the spleen, the possibility of lytic destruction of the spleen cells by the virus during in vitro culture was excluded. In addition, the depression in Con A responsiveness was noted with a wide range of Con A concentrations, and preculture studies failed to result in enhanced reactivity of the cells from infected animals. We conclude that reductions of both B- and T-cell functions, which differ in their timing during the course of acute CMV infection, occur concurrently with an enhanced viral specific immune response in guinea pigs acutely infected with CMV.     

Reaction of human lymphocytes with aggregated IgG columns. Effect on antibody-dependent cytotoxicity and EAC rosette formation.

The origin and life span of long-lived small lymphocytes in the bone marrow of mice have been evaluated by the use of radioautography, scintillation counting, and anti-theta serum. Thymus-deprived BALB/C mice and nude mice had a smaller percentage of long-lived lymphocytes in bone marrow and in thoracic duct lymph than sham-operated or normal littermates. Furthermore, the long-lived lymphocytes in the marrow of nudes have more varied—but generally shorter—life spans than long-lived lymphocytes from mice having a thymus. In thoracic duct lymph of nude mice a more homogeneous long-lived population—according to life span—was found.It was concluded that both long-lived T cells and long-lived B cells are normal residents in the bone marrow. Furthermore, it was concluded that cells of variable life spans comprise the B lymphocyte population: short-lived cells with life spans of 3–5 days and long-lived lymphocytes with life spans of weeks to months.     

Inhibition of lymphocyte proliferation by monoclonal antibody directed against the T3 antigen on human T cells

Peripheral blood mononuclear cells from 40% of normal donors are mitogenically unresponsive to UCHT1, a monoclonal antibody reactive to the T3 surface molecule on human T lymphocytes. Cell preparations from non-UCHT1 responders were used to examine whether and how interaction of UCHT1 with the T3 molecule affects T-cell functionality. It was found that UCHT1 profoundly (greater than 85%) suppressed lymphocyte proliferation induced by plant mitogens (phytohemagglutinin (PHA) and concanavalin A (Con A], recall antigen (candidin), and allogeneic non-T cells. The antibody abrogated both the production of interleukin 2 (IL-2) by and the expression of IL-2-specific receptors on T lymphocytes stimulated by PHA or allogeneic non-T cells. UCHT1 was maximally suppressive when added to cells within 2 hr (PHA stimulation) or 1 day (allogeneic non-T cell activation) after the initiation of the culture period. The inhibiting activity of UCHT1 could be related to its ability to modulate T3 molecules from the T-cell surface: both actions displayed the same antibody concentration dependence and had a comparable time dependence. Moreover, after modulation, unresponsive lymphocytes regained responsiveness to PHA in parallel with reexpression of surface T3 molecules. These findings are consistent with the idea that the human T3 molecule functions as an essential signal transducer during the early phases of T-cell activation.     

Some requirements for the response of separated T-cell sub-populations to the mitogens phytohaemagglutinin and concanavalin A.

The proliferative response of various separated populations of mouse spleen and thymus lymphocytes to the mitogen phytohaemagglutinin (PHA) was not a direct function of the level of responsive T cells, but was governed by other regulatory effects. These included a stimulation by adherent macrophages, an inhibition by a separate population of adherent cells and an adherent cell independent restriction of proliferation at high cell concentration. In contrast, the proliferative response to Concanavalin A (Con A) was more closely related to the level of responsive T cells. All density and electrophoretically isolated sub-sets of splenic T cells appeared capable of a proliferative response to PHA and Con A, although under some conditions the PHA responsiveness of certain fractions was suppressed. In the thymus, the minor low theta sub-population appeared capable of response to both mitogens, and accounted for all the activity of the unfractioned thymus cells. No response to either mitogen could be obtained from the major, high theta thymocyte population.     

Effect of immune reconstitution on resistance to Brugia pahangi in congenitally athymic nude mice

The dichotomy of resistance to Brugia pahangi (Nematoda: Filarioidea) between nonsusceptible, euthymic C3H/HeN mice, heterozygotic for the "nu" gene (+/nu), and susceptible, congenitally-athymic "nude" (nu/nu) C3H/HeN mice, suggests that resistance is thymus-dependent. To test this hypothesis, the effect of syngeneic neonatal thymus grafts and neonatal thymus cell suspensions on recovery of worms at day 40 PI, and responses to Concanavalin A (Con A) were examined in reconstituted nudes. Nude recipients of a thymus graft 7 or 14 wk before subcutaneous inoculation with 50 infective larvae (L3) yielded no worms and responded strongly to Con A. Serum from these mice reacted in two lines of identity with serum from similarly-infected heterozygotes by double radial immunodiffusion against an adult worm saline extract. Nude recipients of a thymus 2 days or 3 wk before inoculation harbored an average of three or two worms, respectively. Intravenous injection of nude recipients with 10(7) or 10(8) neonatal thymus cells seven weeks before inoculation was less effective in conferring resistance to B. pahangi and responsiveness to Con A. Complete resistance to B. pahangi could be adoptively transferred to nude mice by 10(8) spleen cells obtained from infection-primed heterozygotes and injected intravenously on the day of larval inoculation. The same numbers of worms were significantly reduced. less effective when injected 3 wk before inoculation, although numbers of worms were significantly reduced. Passive transfer of primed heterozygote serum, containing high titers of antibodies to adult worm and larval antigens, failed to protect nude recipients against a larval inoculum in the absence of cellular reconstitution.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cell growth and gene rearrangement signals during the development of T lymphocytes within the thymus

The thymus provides signals that control the proliferation and differentiation of T lymphocytes and select the repertoire of T-cell specificities. Antibodies to CD3 molecules inhibit full rearrangement of T-cell receptor beta chain genes in organ cultures of early embryo mouse thymus. Whether this effect is mediated through gamma delta CD3 expressing cells, which are present in small numbers at this stage, or through low amounts of CD3 on alpha beta precursor cells is unclear. A requirement for special gene rearrangement signals within the thymus is supported also by the observations that growth factors such as IL-2 and IL-4, although stimulating proliferation of precursor cells removed from the thymus, do not induce full T-cell receptor gene rearrangements. Recent studies show that newly formed thymic lymphocytes expressing alpha beta CD3 receptors are targets for negative selection (deletion) as a means of removing autoreactive cells. Signalling to immature thymocytes via the alpha beta CD3 complex induces the activation of endogenous endonucleases that cleave DNA into oligonucleosomal fragments. We suggest that the activation of this mechanism is the means by which autoreactive cells are removed.     

The thymus microenvironment in regulating thymocyte differentiation

The thymus plays a crucial role in the development of T lymphocytes providing an inductive microenvironment in which committed progenitors undergo proliferation, T-cell receptor gene rearrangements and thymocyte differentiation into mature T-cells. The thymus microenvironment forms a complex network of interaction that comprises non lymphoid cells (e.g., thymic epithelial cells, TEC), cytokines, chemokines, extracellular matrix elements (ECM), matrix metalloproteinases and other soluble proteins. The thymic epithelial meshwork is the major component of thymic microenvironment, both morphologically and phenotypically limiting heterogeneous regions in thymic lobules and fulfilling an important role during specific stages of T-cell maturation. The process starts when bone marrow–derived lymphocyte precursors arrive at the outer cortical region of the thymic gland and begin to mature into functional T lymphocytes that will finally exit the thymus and populate the peripheral lymphoid organs. During their journey inside the thymus, thymocytes must interact with stromal cells (and their soluble products) and extracellular matrix proteins to receive appropriate signals for survival, proliferation and differentiation. The crucial components of the thymus microenvironment and their complex interactions during the T-cell maturation process with the objective of contributing to a better understanding of the function of the thymus as well as assist in the search for new therapeutic approaches to improve the immune response in various pathological conditions are summarized here.     

Changes in lymphocyte populations in protein—Calorie-deficient mice

Changes in lymphocyte subpopulations induced by postweaning malnutrition were studied in C57BL/6 mice kept on a protein-restricted diet (D), by weekly assessment of the “homing” properties and the response to mitogens of thymus and spleen lymphocytes during the first 2 months of diet. Cell loss in the lymphoid organs during the early phase of protein restriction was mainly due to depletion of nonrecirculating cells. This resulted in relative enrichment of medullary cells in the thymus and T₂ cells in the periphery as shown by the rise in the percentage migration of D lymphocytes to the lymph nodes as well as in their response to optimal doses of PHA and Con A and PHA:Con A response ratio. Reversion of the distribution pattern of D lymphocytes, with depressed homing to the lymph nodes and decrease in the response to mitogens, was observed concomitantly with a second phase of partial recovery in the whole-body weight and cell content of the thymus and spleen. The [³H]thymidine uptake by D spleen cells stimulated with supraoptimal doses of mitogen was significantly increased during the whole length of the experiment. The suppression of DNA synthesis induced by high doses of mitogen reappeared after short-term nutritional rehabilitation.     

Age and dose related alteration of in vitro mixed lymphocyte culture response of blood lymphocytes from A-bomb survivors

The responsiveness of peripheral blood lymphocytes to allogenic antigens in mixed lymphocyte culture (MLC) was measured in 139 atomic-bomb survivors. The study revealed a significant decrease in MLC response with increasing dose of previous radiation exposure. This decline was marked in the survivors who were older than 15 at the time of the bomb (ATB). The results suggest a possible relationship between the recovery of T-cell-related function and the thymic function which processes mature T cells for the immune system. Thus it may be that in the advanced age ATB group, the thymus function had started to involute, allowing less recovery of T-cell function compared to young survivors who had adequate processing T-cell activity.     

The thymus microenvironment in regulating thymocyte differentiation

The thymus plays a crucial role in the development of T lymphocytes by providing an inductive microenvironment in which committed progenitors undergo proliferation, T-cell receptor gene rearrangements and thymocyte differentiate into mature T cells. The thymus microenvironment forms a complex network of interaction that comprises non lymphoid cells (e.g., thymic epithelial cells, TEC), cytokines, chemokines, extracellular matrix elements (ECM), matrix metalloproteinases and other soluble proteins. The thymic epithelial meshwork is the major component of the thymic microenvironment, both morphologically and phenotypically limiting heterogeneous regions in thymic lobules and fulfilling an important role during specific stages of T-cell maturation. The process starts when bone marrow-derived lymphocyte precursors arrive at the outer cortical region of the thymic gland and begin to mature into functional T lymphocytes that will finally exit the thymus and populate the peripheral lymphoid organs. During their journey inside the thymus, thymocytes must interact with stromal cells (and their soluble products) and extracellular matrix proteins to receive appropriate signals for survival, proliferation and differentiation. The crucial components of the thymus microenvironment, and their complex interactions during the T-cell maturation process are summarized here with the objective of contributing to a better understanding of the function of the thymus, as well as assisting in the search for new therapeutic approaches to improve the immune response in various pathological conditions.Key words: thymus, T-cell maturation, thymic microenvironment, thymocyte differantiation, chemokines, extracellular matrix, thymic nurse cells, metalloproteinases     

Rat thymus reconstitution after thymocyte destruction by glucocorticoid treatment--from the view of endogenous DNA synthesis and soybean lectin responsiveness in thymocytes

The dynamic process in rat thymocyte restoration after their destruction by glucocorticoid (GC) administration was examined. Thymus weight and thymocyte count became minimal 4-5 days after the administration. Then the thymus took a course of recovery. Endogenous DNA synthesis in thymocytes, reflecting their proliferation within thymus, decreased for 4 days but began to increase 6-8 days after GC treatment. Thymocyte responsiveness to soybean lectin (SBL), a possible stimulator for T-cell-precursors, showed elevation 4-5 days after the treatment. A marked decrease of lymphocytes in the cortex and unclearness of cortico-medullary junction were observed 2-3 days after GC treatment. Clusters of small lymphoid cells, which possibly contained SBL-responding cells, were found in the subcapsular area 4 days after the treatment and successively, large lymphocytes became visible in the same area. Thereafter, small lymphocytes in the cortical mid and deep zones increased, and cortico-medullary junction was restored. These histological features are discussed from the view of correspondence with the dynamic changes of endogenous DNA synthesis and SBL responsiveness in the thymocytes after GC administration.