Demonstration of large-scale migration of cortical thymocytes to peripheral lymphoid tissues in cyclosporin A-treated rats

Metallophilic macrophages of the rodent thymus

For a very long time, we studied the metallophilic macrophages of the rodent thymus and in this review our results on morphological, histochemical, enzymehistochemical, immunohistochemical, ultrastructural and functional features of these cells, as well as the molecular regulation of their development, will be presented. Furthermore, the differences between species will also be discussed and the comparisons with similar/related cell types (metallophilic macrophages in the marginal sinus of the spleen, subcapsular sinus of the lymph nodes and germinal centers of secondary lymphoid follicles) will be made. Metallophilic macrophages are strategically positioned in the thymic cortico-medullary zone and are very likely to be involved in: (i) the metabolism, synthesis and production of bioactive lipids, most likely arachidonic acid metabolites, based on their histochemical and enzymehistochemical features, and (ii) the process of negative selection that occurs in the thymus, based on their ultrastructural features and their reactivity after the application of toxic or immunosuppressive/immunomodulatory agents. Taken together, their phenotypic and functional features strongly suggest that metallophilic macrophages play a significant role in the thymic physiology.

Clinical factors influencing T-cell receptor excision circle (TRECs) counts following allogeneic stem cell transplantation in adults

To ascertain the clinical factors involved in T-cell reconstitution after allogeneic stem cell transplantation (SCT), we evaluated serial assessments of lymphocyte subsets by flow cytometry and TRECs levels by quantitative PCR in 83 adult patients. Patient age >25 years, unrelated donor, CMV infection and acute graft-versus-host disease (GVHD) adversely affected CD3(+) and CD8(+) T-cell recovery after SCT (p < 0.05). TRECs were low or undetectable during the first months after transplant and progressively increased thereafter. However, median TRECs of patients did never achieve normal values compared to healthy donors (median follow-up 9 months, range 2-42). Presence and severity of chronic GVHD significantly affected TRECs counts: patients with chronic GVHD had lower TRECs than patients without GVHD at 9, 12 and 24 months after SCT (p = 0.002, p = 0.022, p = 0.015). Patients with limited chronic GVHD had higher TRECs compared to patients with extensive GVHD (p = 0.018). No relationship was observed between fungal or bacterial infections and TRECs. Nonetheless, CMV infection was associated with lower TRECs (p = 0.032). Our data support the concept that adult thymus contributes with a slow but continuous production of thymic T cells to immune reconstitution after SCT. Chronic GVHD is the main factor associated to a delay in TRECs counts recovery.

Cyclical mobilization and gated importation of thymocyte progenitors in the adult mouse: evidence for a thymus-bone marrow feedback loop

It has recently been observed, as in the fetal thymus, that the importation of hematogenous thymocyte progenitors by the adult thymus is a gated phenomenon, whereby saturating numbers of progenitors periodically enter the thymus and occupy a finite number of intrathymic niches. In addition, the mobilization of thymocyte progenitors from the bone marrow appears to be a cyclical process that coincides temporally with the periods of thymic receptivity (open gate). It is proposed that these events are coordinated by a thymus-bone marrow feedback loop in which a wave of developing triple negative (CD3- CD4- CD8-) thymocytes interacts with stromal cells in the stratified regions of the thymus cortex to sequentially induce the release of diffusible cytokines that regulate the production, mobilization, and recruitment of thymocyte progenitors. The likely components of this feedback loop are described here, as are the properties of the intrathymic vascular gates and niches for thymocyte progenitors. The cyclical production and release of thymocyte progenitors from the bone marrow is placed in the context of a general phenomenon of oscillatory feedback regulation involving all lymphohemopoietic cell lineages. Lastly, the question of whether the gated (as opposed to the continuous) entry of thymocyte progenitors is essential for normal thymocytopoiesis in adult life is discussed.

In vivo and in vitro modulation of MDR molecules in murine thymocytes

P-glycoprotein (Pgp/ABCB1) and multidrug resistance related protein 1 (MRP1/ABCC1) were first described in multidrug resistant tumor cells. It is presently known that both proteins are also expressed in a variety of normal cells, including lymphocytes. ABCB1 activity has already been detected in subpopulations of murine thymocytes, but there was little information on the expression or activity of ABCC1 in these cells. The present work studied in mice the expression of both proteins by RT-PCR and immunofluorescence. It was possible to identify the presence of ABCB1 and to detect the expression of ABCC1 in these cells. The functional activities of these proteins were also studied in vivo and in vitro measuring the extrusion of fluorescent dyes in association with MDR modulators. Cyclosporine A, verapamil and trifluoperazine inhibited the activity of thymic ABCB1. Indomethacin, probenecid and MK571 were effective in inhibiting ABCC1 activity by thymic cells. ABCB1 was only active in a small percentage of thymocytes being present in the immature double negative (not CD4 nor CD8) subpopulation and the mature single positive (CD4 or CD8) subpopulations. The functional activity of ABCC1, on the other hand, was more homogeneously distributed being found in all thymocyte subpopulations. Possible physiological roles for these transporters on thymocytes are discussed.

Terminal deoxynucleotidyl transferase-positive cells in human tonsils

To study the possible cellular origin of recently recognized indolent terminal deoxynucleotidyl transferase (TdT)-positive T-lymphoblastic proliferations of the tonsils and oropharynx, we studied normal human tonsils for the presence of TdT-positive cells. TdT-positive cells were readily demonstrated in the tonsils from 15 children and adults by immunohistochemical staining. TdT-positive cells were distributed in discrete foci at the periphery of lobules of lymphoid tissue and adjacent to fibrous septa and had the morphologic features of small to medium-sized lymphocytes. Double-antibody staining indicated the TdT-positive cells had the phenotype of uncommitted early lymphoid precursors (CD3-, CD79a-, CD10-). Foci of TdT-positive cells were not identified in 6 reactive lymph nodes studied as controls. These studies indicate that tonsils, like bone marrow and thymus, are sites of lymphopoiesis. The presence of TdT-positive precursor cells in human tonsils may be a factor in the pathogenesis of recently described indolent T-lymphoblastic proliferations involving the tonsils and oropharynx. The presence of TdT-positive cells in human tonsils should not be misinterpreted as evidence of lymphoblastic lymphoma or leukemia.

Tolerance to cyclosporin A-induced autologous graft-versus-host disease is mediated by a CD4+CD25+ subset of recent thymic emigrants

Our previous studies revealed that both the autoeffector and immunoregulatory T cells in cyclosporin A (CSA)-induced autologous graft-vs-host disease are recent thymic emigrants (RTEs). The autoeffector cells appear in and are released from the thymus during the first week of CSA treatment, whereas the immunoregulatory thymocytes appear during the second week but are not released until several days after cessation of CSA treatment. In the present study, the antigenic phenotypes of these functional T cell subsets were determined by immunomagnetic separation and flow immunocytometric analysis. During CSA wk 1, the autoeffector T cells in both the thymus and lymph node (LN) expressed a CD4+8+ double-positive (DP) phenotype, after which those in the LN became CD8 single positive (SP). Timed thymectomy experiments confirmed that the CD8-SP autoeffector T cells in LN originated from these DP RTEs. During CSA wk 2, the immunoregulatory thymocytes also displayed a DP phenotype. However, they were not exported to the periphery until several days after CSA treatment had been interrupted and they had acquired a CD4-SP phenotype. In LN, these immunoregulatory RTEs expressed the CD25+ marker characteristic of anergic/suppressor T cells. Cell separation and mixing experiments demonstrated that the autoeffector T cells persist in LN after cessation of CSA treatment, but their activity is not detectable in the presence of recently exported CD4+ T cells. Hence, the results indicate that tolerance to CSA-induced autologous graft-vs-host disease is actively mediated by CD25+CD4+ RTEs that suppress the function of CD8 autoeffector T cells.

Factors affecting thymic function after allogeneic hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is followed by profound immunodeficiency. Thymic function is necessary for de novo generation of T cells after HSCT. Circulating CD45RA(+) naive T-cell levels are predictive of antigen-specific T-cell responses in the absence of graft-versus-host disease (GVHD). These T cells may not represent recent thymic emigrants, since naive T cells may maintain this phenotype if not antigen-activated. To accurately measure thymic output after HSCT and determine the factors that influence thymic function, T-cell receptor excision circles (TRECs) were examined in CD4(+) and CD8(+) cells from a cross-section of patients following HSCT. TREC levels rose weeks after HSCT and could be detected in patients 6 years after HSCT. TREC levels correlated with the frequency of phenotypically naive T cells, indicating that such cells were not expanded progeny of naive T cells present in the donor graft. Chronic GVHD was the most important factor that predicted low TREC levels even years after HSCT. Patients with a history of resolved GVHD had decreased numbers of TREC, compared with those with no GVHD. Because few adults had no history of GVHD, it was not possible to determine whether age alone inversely correlated with TREC levels. Recipients of cord blood grafts had no evidence of decreased TREC induced by immunosuppressive prophylaxis drugs. Compared with unrelated donor grafts, recipients of matched sibling grafts had higher TREC levels. Collectively, these data suggest that thymopoiesis is inhibited by GVHD. Larger studies will be needed to determine the independent contributions of age and preparative regimen to post-transplant thymopoietic capacity.

Cyclosporin A-Induced Autologous Graft-Versus-Host Disease: A Prototypical Model of Autoimmunity and Active (Dominant) Tolerance Coordinately Induced by Recent Thymic Emigrants

Cyclosporin A (CSA)-induced autologous graft-vs-host disease (autoGVHD) is an autoimmune syndrome initiated by autoeffector T cells presumed to be exported from the thymus during CSA treatment. The appearance of noncytotoxic immunoregulatory T cell activity after cessation of CSA treatment is also thymus dependent. In the present study, we have tested the hypothesis that both autoeffector and immunoregulatory T cells in CSA-treated rats are recent thymic emigrants (RTEs). Local syngeneic graft-vs-host reaction (synGVHR) and timed thymectomy (Tx) assays revealed that autoeffector T cells appear initially in the thymus and are promptly exported to lymph nodes (LN) during the first week of CSA treatment. In contrast, immunoregulatory thymocytes are first detectable by local synGVHR inhibition assays during the second week of CSA treatment but are not exported to LN until ∼4 days post-CSA. Both the autoeffector and immunoregulatory T cells in LN express Thy-1, a selective marker for RTEs in the rat. However, the autoeffector RTEs have a CD4+8+ phenotype, whereas the immunoregulatory RTEs have a CD4+8− phenotype. Thus, the coordinate formation in and release from the thymus cortex and medulla of autoeffector and immunoregulatory T cells in CSA-treated rats directly demonstrates that centrally induced, nondeletional tolerance can serve as a fail-safe mechanism by which clones of autoeffector T cells that have escaped intrathymic negative selection for self-MHC class II Ag can be suppressed postthymically.

The fate of thymocytes labeled in vivo with CFSE

The fate of thymic emigrants had so far been studied using a variety of markers, each of which had inherent limitations as to stability, toxicity, or selectivity. We describe a new technique which relies on the in vivo injection of CFSE, an esterified vital dye hitherto used at 80 times lower concentrations for in vitro cell labeling. We show that CFSE labels a representative sample of all thymocyte subsets and that these migrate at a rate of approximately 2-3 x 10(6) cells/day to peripheral lymphoid organs. We show that they enter lymph nodes at day 1 postinjection and stay for at least 21 days, whereas the turnover in the spleen is more rapid. We also show by immunohistochemistry, using peroxidase-labeled anti-FITC antibodies, that CFSE-labeled thymic emigrants are confined to T-dependent areas of peripheral lymphoid organs.

Mercury-induced autoimmunity in Brown Norway rats: kinetics of changes in RT6+ T lymphocytes correlated with IgG isotypes of circulating autoantibodies to laminin 1

Repeated exposure to mercury causes various autoimmune effects in rats of the Brown Norway (BN) strain. Previous studies from our laboratory have shown that on day 15 of HgCl2 treatment BN rats exhibit a relative decrease in RT6.2+ T cells. At the same time, they produce high levels of autoantibodies to renal antigens and experience a membranous glomerulonephropathy. In contrast, Lewis (LEW) rats are resistant to autoimmunity caused by mercury and do not demonstrate a decrease in RT6+ cells after administration of HgCl2. In the present paper we provide novel information on the correlation between changes in RT6.2+ lymph node T cells and the production of autoantibodies to laminin 1, obtained by detailed kinetic studies of HgCl2-treated BN rats. We have confirmed a decrease in the percentage of RT6.2+ lymphocytes on day 15 of mercury treatment, despite a significant increase in the number of peripheral lymphocytes. No such changes were observed in LEW rats. We have determined that on day 15 the percentage decrease in RT6+ cells is evident in both RT6.2+CD4+ and RT6.2+CD8+ T cell subsets. Kinetic studies demonstrated that significant changes in the percentage of RT6.2+ cells are first observed by day 8 and continue through days 11 and 15. We have also observed a significant percent decrease in CD4+ T lymphocytes as well as an increase in CD4-CD8- cells. The dramatic increase in the percentage of these double negative cells at the level of peripheral lymphoid tissues does not appear to be due to higher thymic output, since there was a decrease in the percentage of TCR+Thy1+ cells, a phenotype that is associated with recent thymic emigrants. Finally, we have demonstrated that 100% of HgCl2-treated BN rats had circulating antibodies that reacted with both mouse and rat laminin 1, i.e. are autoantibodies to laminin 1. These autoantibodies were predominantly of the IgG1 and IgG2a isotype, possibly as the result of a polarized autoimmune response driven by Type 2 cytokines. A kinetic investigation showed that significant levels of IgG1 and IgG2a autoantibodies to laminin 1 were first presentin the circulation by day 11. The inverse correlation between levels of RT6.2+ T lymphocytes and autoantibodies to laminin 1 suggests that mercury may induce autoimmune responses in BN rats by its effects on these immunoregulatory cells.

Cyclosporin A inhibits early mRNA expression of G0/G1 switch gene 2 (G0S2) in cultured human blood mononuclear cells

Cyclosporin A (CsA) may achieve its immunosuppressive effects by inhibiting the calcium- and calmodulin-dependent phosphatase calcineurin which is required for activation of target genes by members of the NFAT (nuclear factor of activated T cells) transcription factor family. Among these target genes is the gene encoding interleukin-2 (IL2), a cytokine facilitating progression through the G1 phase of the cell cycle. However, IL2 does not reverse CsA inhibition, suggesting that at least one other NFAT-sensitive gene may be involved. The human G0/G1 switch gene, G0S2, has potential NFAT-binding sites in the 5' flank and encodes a small basic potential phosphoprotein of unknown function. Using a sensitive, reverse transcription-polymerase chain reaction (RT-PCR) assay, G0S2 mRNA levels were assayed in cultured blood mononuclear cells. Freshly isolated cells contain high levels of G0S2 mRNA which rapidly decline. This "spontaneous stimulation" is also noted with some other G0S genes and has been attributed to some aspect of the isolation procedure. In cells that have been preincubated to lower mRNA levels, there is a transient increase in G0S2 mRNA, peaking between 1-2 h, in response to Concanavalin-A (ConA), or to the combination of phorbol ester (TPA), and the calcium ionophore, ionomycin. Both these responses are inhibited by CsA. Our results suggest that G0S2 expression is required to commit cells to enter the G1 phase of the cell cycle, and that, while not excluding other possible targets, early inhibition of G0S2 expression by CsA may be important in achieving immunosuppression. G0S2 may be of value as a reporter gene for analyzing the mechanism of action of CsA and its influence on the positive and negative selection of lymphocytes in response to self and not-self antigens.

Differential effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin, bis(tri-n-butyltin) oxide and cyclosporine on thymus histophysiology

Recent advances in the histophysiology of the normal thymus have revealed its complex architecture, showing distinct microenvironments at the light and electron microscopic level. The epithelium comprising the major component of the thymic stroma is not only involved in the positive selection of thymocytes, but also in their negative selection. Dendritic cells, however, are more efficient than epithelial cells in mediating negative selection. Thymocytes are dependent on the epithelium for normal development. Conversely, epithelial cells need the presence of thymocytes to maintain their integrity. The thymus rapidly responds to immunotoxic injury. Both the thymocytes and the nonlymphoid compartment of the organ can be targets of exposure. Disturbance of positive and negative thymocyte selection may have a major impact on the immunological function of the thymus. Suppression of peripheral T-cell-dependent immunity as a consequence of thymus toxicity is primarily seen after perinatal exposure when the thymus is most active. Autoimmunity may be another manifestation of chemically mediated thymus toxicity. Although the regenerative capacity of thymus structure is remarkable, it remains to be clarified whether this also applies to thymus function. In-depth mechanistic studies on chemical-induced dysfunction of the thymus have been conducted with the environmental contaminants 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and bis(tri-n-butyltin)oxide (TBTO) as well as the pharmaceutical immunosuppressant cyclosporine (CsA). Each of these compounds exerts a differential effect on the morphology of the thymus, depending on the cellular targets for toxicity. TCDD and TBTO exposure results in cortical lymphodepletion, albeit by different mechanisms. An important feature of TCDD-mediated thymus toxicity is the disruption of epithelial cells in the cortex. TBTO primarily induces cortical thymocyte cell death. In contrast CsA administration results in major alterations in the medulla, the cortex remaining largely intact. Medullary epithelial cells and dendritic cells are particularly sensitive to CsA. The differential effects of these three immunotoxicants suggest unique susceptibilities of the various cell types and regions that make up the thymus.

Immunobiology and immunotherapeutic implications of syngeneic/autologous graft-versus-host disease

Administration of the immunosuppressive drug cyclosporine (CsA) after syngeneic/autologous bone marrow transplantation (BMT) elicits an autoimmune syndrome with pathology virtually identical to graft-vs-host disease (GVHD). The induction of this syndrome, termed syngeneic/autologous GVHD, is a two-tiered process requiring both the active inhibition of thymic-dependent clonal deletion and the elimination of mature T cells that have an immunoregulatory effect. Eradication of the peripheral immunoregulatory compartment by the preparative regimen provides a permissive environment for the activation of the syngeneic/autologous GVHD effector T cells. Although the repertoire of autoreactive effector T lymphocytes is highly conserved, these T cells promiscuously recognize MHC class II determinants. This novel specificity of the autoreactive lymphocytes appears to be dependent on the peptide derived from the MHC class II invariant chain. Recent studies also suggest that these promiscuous autoreactive T cells can effectively target and eliminate MHC class II-expressing tumor cells. Administration of cytokines that upregulate the target antigen or expand the effector population can potentiate the antitumor activity of syngeneic/autologous GVHD. Although the induction of syngeneic/autologous GVHD is an untoward effect of CsA immunosuppression, mobilization of these autoimmune mechanisms provides a promising immunotherapeutic approach for certain neoplastic diseases.

Prevention of Transplant Rejection: Can Tolerance be Achieved with Immunosuppressive Treatment?

Successful solid organ transplantation is generally attributed to the increasingly precise ability of drugs to control rejection. However, it was recently shown that a few donor haematolymphoid cells can survive for decades in recipients of successful organ allografts, a phenomenon called microchimaerism. The association for decades of haematolymphoid chimaerism with allograft tolerance in experimental transplantation suggests that immunosuppressive drugs merely create a milieu that enables an allograft and its complement of passenger leucocytes to prime the recipient for graft acceptance.Exploitation of this concept requires a fundamental shift in the classical view of passenger leucocytes only as initiators of rejection. Microchimaerism has taught us that solid organ transplantation involves the transfer of two donor organ systems to the recipient: the allograft parenchyma and the donor haematolymphoid system in the form of donor stem cells contained within the passenger leucocyte compartment. Each has the potential to integrate with the corresponding recipient system and carry out normal physiological functions, such as immunological self definition. Resistance to initial integration by mature T cells requires some form of immunosuppression, but maintenance of donor immune system function will depend on renewable supply of cells, which can be provided by engrafted progenitors. Successful clinical application will depend on the development of low morbidity methods to enhance engraftment of donor haemopoietic stem cells.

Alterations of dendritic cells in the rat thymus without epithelial cell loss during cyclosporine treatment and recovery

After cyclosporine treatment, dendritic cells disappear from the rat thymic medulla. The present study was undertaken to examine the ultrastructural alterations in the dendritic cell population during 14-day cyclosporine treatment and subsequent 6-week recovery. Four dendritic cell subtypes were defined ultrastructurally by a newly developed classification system. In addition, the potential effect of cyclosporine on six medullary epithelial cell subtypes was studied. During cyclosporine treatment, a prominent reduction of dendritic cells was seen at the ultrastructural level, whereas the total number of medullary epithelial cells remained largely unchanged. These findings were confirmed by immunohistochemistry. The number of mature dendritic cells declined later than the number of immature ones. A decrease in the antigen-processing capacity of remaining dendritic cells was suggested by the disappearance of Birbeck granules and the reduced number of tubulovesicular complexes. These findings support a disturbance of clonal deletion during cyclosporine treatment. The dendritic cell alterations appeared reversible 4 weeks after the restoration of the original architecture. During recovery, dendritic cells displaying lysosomal elements outnumbered those found in the normal uninvoluted thymus. This phenomenon probably reflects an enhanced turnover of cell organelles. No treatment-related effect on epithelial cell subtypes was seen.

Evidence for involvement of superantigens in human periodontal diseases: skewed expression of T cell receptor variable regions by gingival T cells

Immunomodulation by periodontopathic bacteria has been implicated in the pathogenesis of inflammatory periodontal diseases. A novel class of microbial-derived T cell mitogens, referred to as superantigens, has recently been described. Superantigens are unique in that they induce a tremendous activation and expansion of specific subsets of T cells in an antigen-independent manner, thereby causing immune dysfunction. Subsets of superantigen-expanded T cells can be identified with reagents that discriminate among different families of the variable domains of the T cell antigen receptor beta-chain (V beta). Since superantigens expand one or a few of these T cell antigen receptor V beta families, T cell subsets that have been expanded by superantigens have restricted expression of one or a few V beta families. In the present study, we investigated the presence of putative superantigen-stimulated T cells in periodontitis sites, utilizing a panel monoclonal antibodies to T cell antigen receptor V beta families. Leukocytes were isolated from gingival tissues obtained from 8 periodontitis and 4 non-periodontitis patients by collagenase digestion. Three-color flow cytometric analysis of these gingival cells demonstrated that in most periodontitis patients examined, patterns of V beta expression among T cells are characteristic of superantigen stimulation, i.e., there is an elevation in the proportion of one or a few V beta families. Specifically, these analyses revealed that T cell subsets expressing V beta 5a and V beta 5b, V beta 6, V beta 8 and V beta 12 were each elevated greater than 2 standard deviations in at least one periodontitis patient compared with the mean of the non-periodontitis subjects. In some periodontitis patients, a less marked elevation of T cells that express V beta 3, V beta 5a, V beta 5b, V beta 6, V beta 8, V beta 12, and V beta 13 was noted (greater than 1 standard deviation higher than the mean of the V beta families in non-periodontics subjects). Interestingly, V beta 8+ T cells were elevated to some degree in all periodontitis patients examined. In contrast, T cells expressing V beta 2, V beta 17 and V beta 19 were not significantly different in any of the subjects studied. In most periodontitis but not non-periodontitis patients, up to 50% of all gingival T cells expressed one or a few T cell antigen receptor V beta families, suggesting that superantigens constitute a major pathway of T cell activation and expansion. Hence, our data support the hypothesis that a large proportion of T cells in periodontitis sites have been stimulated and expanded by superantigens, presumably produced by periodontitis-associated bacteria.

Post-thymectomy autoimmunity: abnormal T-cell homeostasis

Thymectomy of 3-day-old mice induces organ-specific autoimmune disease, which is characterized by the presence of autoantibodies and T-cell infiltrates in the affected organs. Here, Adriana Bonomo and colleagues propose a new model for the pathogenesis of this syndrome, which integrates many of the homeostatic mechanisms of the immune system, including central and peripheral tolerance, T-cell maturation and exportation from the thymus, as well as lymphocyte recirculation and homing.

Impairment of B and T cell maturation in gut associated lymphoid tissues due to malnutrition during lactation

Previously we found that malnutrition during lactation in rats produces an impairment in the immune response to cholera toxin. In this report we found that malnutrition during lactation provokes in 28-day-old rats an increase of Thy1+ c mu+ cells in gut associated lymphoid tissues concomitantly with a decrease of sIgA+ B cells. No differences were found in the percentages of the IgM+ B cell populations. Furthermore, no differences were found in the Peyer's patch (PP) and mesenteric lymph node (MLN) T cell subsets in weaning rats when compared to controls. However, after 1 week of refeeding a higher percentage of the Thy1+ c mu- subset together with a lower percentage of CD5+, CD4+, and CD8+ T cells, were found in malnourished rats when compared to controls. The above results may indicate that B-cell maturation is delayed in malnourished rats at two stages of differentiation: (a) in the passage of pre-B cells (Thy1+ c mu+) to immature B cells (s mu+), and (b) in the switch from s mu+ B cells to s alpha+ B cells. The decrease of CD5+, CD4+, and CD8+ T cells together with an increase of the Thy1+ c mu- subset in gut-associated lymphoid tissues (GALT) may indicate that T-cell maturation is also delayed. Results obtained at weaning may be due to an engraftment by maternal milk-derived lymphocytes in the pups.

Neonatal injections of cyclosporin enhance autoimmune diabetes in non-obese diabetic mice

Since the modulation of the immune system at birth may influence the course of insulin-dependent (type 1) diabetes, we investigated whether neonatal injections of cyclosporin (CsA) to newborn non-obese diabetic (NOD) mice influence diabetes during later life. Two groups of 90 mice (45 female, 45 male) were injected intraperitoneally for the first 6 days of life with CsA (10 mg/kg per day) or with vehicle. In female NOD mice, the onset of diabetes was earlier and cumulative incidence was higher after neonatal treatment with CsA (P < 0.01). The incidence of diabetes was also dramatically enhanced in male NOD mice (P < 0.01), which normally display a very low disease incidence. Concomitantly, the severity of lymphocytic infiltration of the pancreatic islets was higher in female NOD mice neonatally treated by CsA (P < 0.02), and to a lesser extent in males, than in control mice. After administration of CsA to newborn NOD mice, there was a reduction (P < 0.01) of both CD4+CD8- and CD4-CD8+ thymocytes, whereas the number of double positive CD4+CD8+ thymocytes was increased. Concomitantly, Thy1-2+ cells in spleen were decreased (P < 0.01), and spleen cells expressing either CD3 molecule or alpha beta TCR complex were diminished (P < 0.01). Both CD4+ and CD8+ spleen T cells were depleted. By contrast, the low percentage of gamma delta TCR-expressing splenocytes was not modified. Numbers of MHC class 1+ or MHC class 2+ spleen cells were also depressed (P < 0.01). After neonatal injections of CsA, spleen cells showed a reduced response to concanavalin A (Con A) (P < 0.01). On the contrary, stimulation indices of splenocytes incubated with xenogeneic insulin-producing cell extracts were enhanced (P < 0.03). Proliferation indices of splenocytes to self class 2 antigens, generating suppressor cell activity, during syngeneic mixed lymphocyte reaction (SMLR) were significantly reduced (P < 0.01). Irradiated NOD mice were used as recipients for spleen cells from CsA-neonatally treated NOD mice. They displayed enhanced insulitis 2 weeks after transfer, and diabetes was successfully produced by 1 month after transfer in 50% of the recipients. By contrast, NOD mice which received control syngeneic spleen cells remained normoglycaemic, with only moderate islet infiltration which would be expected of NOD mice of this age. Thus, neonatal injections of CsA markedly enhance diabetes in both female and male NOD mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Xenobiotics, chimerism and the induction of tolerance following organ transplantation

The successful results seen after organ transplantation are largely attributable to the potency and specificity of modern immunosuppressive agents. Although drug-free unresponsiveness to graft alloantigens has not been routinely achieved in clinical practice, recent appreciation of the importance of cell chimerism, which develops after the migration from donor to host of leukocytes contained in solid organ grafts, has introduced a concept which may explain the mechanism of graft tolerance. Recent evidence has indicated that immunosuppressive drugs may have a common potential to induce graft tolerance, even though they act through diverse mechanisms, and that this potential may be mediated by a permissive effect on the migration and survival of donor-derived leukocytes. This review briefly examines the mechanisms by which immunosuppressive drugs function and analyses the different methods which these agents might use to induce chimerism associated with graft tolerance. Furthermore, we describe ongoing clinical studies in which the chimerism produced after solid organ transplantation is augmented with donor bone marrow in an attempt to facilitate the induction of tolerance.