Differential effect of cyclosporine in vivo on the distribution of T cell subsets in the thymus, spleen, and lymph nodes

Safety of attenuated smallpox vaccine LC16m8 in immunodeficient mice

Freeze-dried live attenuated smallpox vaccine LC16m8 prepared in cell culture has been the sole smallpox vaccine licensed in Japan since 1975 and was recently recommended as a WHO stockpile vaccine. We evaluated the safety of recently remanufactured lots of LC16m8 using a series of immunodeficient mouse models. These models included suckling mice, severe combined immunodeficiency disease (SCID) mice, and wild-type mice treated with cyclosporine. LC16m8 showed extremely low virulence in each of the three mouse models compared with that of its parental strains, Lister and LC16mO. These results provide further evidence that LC16m8 is one of the safest replication-competent smallpox vaccines in the world and may be considered for use in immunodeficient patients.

Conditioned taste aversion produced by cyclosporine A: concomitant reduction in lymphoid organ weight and splenocyte proliferation

The classical conditioning of immune parameters is commonly conducted within a conditioned taste aversion (CTA) paradigm. In this study, the immunosuppressive drug cyclosporine A (CsA) was investigated for its ability to produce both taste aversion to a novel stimulus and conditioned alterations in immune functioning. The paradigm comprised the pairing of a 0.2% saccharin solution (the conditioned stimulus; CS) with an intraperitoneal injection of 20 mg/kg CsA (the unconditioned stimulus; UCS). Upon saccharin re-presentation, a marked reduction in fluid consumption was observed, indicating aversion to the novel substance (=CTA). By using a single CsA/saccharin pairing the CTA lasted for one CS representation. However, by implementing three pairings, this effect could be extended for up to seven representations. No noticeable difference was recorded by adjusting the saccharin representation from every consecutive day to every second day. The most effective paradigm in creating CTA was subsequently investigated for its effectiveness in producing conditioned immune alterations. Animals were killed on the day of the third CS re-presentation, and immune functions assessed. Conditioned animals displayed a significant reduction in thymus and spleen weights. Effects on the spleen were further investigated, revealing a significantly reduced proliferative ability of isolated splenocytes to concanavalin A. These results demonstrate that the physiological effects produced by CsA are sufficiently salient to elicit CTA. Furthermore, the reduction in lymphoid organ weight and splenocyte proliferation induced by CsA are also conditionable using this paradigm.

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.

Induction of apoptosis in mouse thymocytes by cyclosporin A: an in vitro study

The effect of cyclosporin A (CsA) on mouse thymocytes was investigated in vitro. Ultrastructural examination and DNA electrophoresis of 24hr-CsA-treated thymocytes showed chromatin condensation, cellular shrinkage and nuclear fragmentation in oligonucleosomal fragments. DNA labeling of CsA-treated-thymocytes with propidium iodide (PI) showed an increase in the number of apoptotic nuclei compared to untreated thymocytes. Furthermore, flow cytometric analysis using monoclonal antibodies (mAbs) specific to particular thymocyte subsets showed that CsA induces a decrease in the relative number of immature double positive (DP) CD4+CD8+ thymocytes in direct proportion to the concentration of CsA. No significant changes were observed in mature single positive (SP) CD4+CD8- and CD8+CD4- cells. Moreover, the cell viability of CsA-treated thymocytes was decreased. These results suggest that CsA induces the programmed cell death of thymocytes in vitro. Taken together with our previous study on the in vivo effect of CsA on mouse thymus and thymocytes, the present study confirms that, in addition to its effect on the thymic epithelium, CsA acts directly on thymocytes by inducing their programmed cell death. We postulate that immature DP thymocytes are the most likely targets of CsA.

Induction of apoptosis in mouse thymocytes by cyclosporin A: in vivo study

We investigated the in vivo effect of cyclosporin A (CsA) on mouse thymus and thymocytes. Administration of CsA (10 mg/kg of body weight) was found to induce a marked reduction in the size, weight and consistency of the thymus. These modifications were associated with thymic reticulo-epithelial cells (TREC) and thymocyte damage. Some of the damaged thymocytes displayed characteristic of cells undergoing apoptosis. Ultrastructural study of thymocytes and thymic tissue, as well as DNA electrophoresis of thymocytes, showed chromatin condensation, cellular shrinkage, and nuclear fragmentation in oligonucleosomal fragments. DNA labeling with propidium iodide (PI) of thymocytes from CsA treated mice cultured for 24 hrs showed an increased number of apoptotic nuclei. Furthermore, flow cytometric analysis using monoclonal antibodies (mAbs) specific for thymocyte subsets confirmed that CsA induces a large decrease in the relative number of mature single positive (SP) CD4+CD8- and CD8+CD4- thymocytes expressing high densities of CD3 and T cell receptor ab (TCR alpha beta) surface molecules, but also a decrease in the absolute number of the other thymocyte subsets. These results suggest that CsA causes macroscopic and ultrastructural modifications of the thymus, associated with an active process of cell death in mouse thymocytes in vivo. In line with these results we formulate a hypothesis concerning the stage of T-cell development at which CsA induces apoptosis.

A novel immunosuppressant, IR-1116, which has a different biological mechanism from that of cyclosporine A

The effects of an epifumagillol derivative, IR-1116, on human lymphocytes in vitro, mouse antibody production in vivo and rat renal and cardiac transplantation were investigated. IR-1116 suppressed the human primary mixed lymphocyte reaction (MLR) in a dose-dependent manner with a value of the dose required for 50% suppression of 0.32 microM. IR-1116 suppressed the antibody production by human B lymphocytes activated with pokeweed mitogen or Epstein-Barr virus, but did not affect the interleukin-2 production by human lymphocytes stimulated with phytohemagglutinin. Furthermore, IR-1116 did not have any effect on the proliferation of B or T lymphocytes. IR-1116 is thought to have a different mechanism from cyclosporine A (CsA). BALB/c mice were immunized by s.c. injection of bovine gamma-globulin (BGG) and then received IR-1116 or CsA by i.p. injection at a dose of 20 mg/kg every other day for 2 weeks. IR-1116 suppressed the production of serum antibodies against BGG as strongly as CsA. In this experiment, IR-1116 apparently showed no adverse effects, while CsA-treated mice suffered from diarrhea and appeared to be irritated. Histological studies showed that IR-1116 suppressed the formation of germinal centers in the spleen of immunized mice. Flow cytometric analysis showed that IR-1116 caused a reduction of B lymphocyte population in splenocytes. On the other hand, CsA caused a marked reduction of helper T lymphocyte population in splenocytes and thymocytes. Furthermore, the i.p. administration of IR-1116 prolonged the survival time in a rat renal allograft model and the vital period of grafted hearts in rats. Based on the above, IR-1116 seems to be a new type of immunosuppressant acting via novel mechanisms different from those of immunosuppressants such as CsA, a potent T lymphocyte suppressant.

Loss of medullary dendritic cells in the thymus after cyclosporine and irradiation

Cyclosporine (CsA) induces a paradoxical graft-vs-host-like disease (GVHD) in syngeneic rat chimeras, providing the rat has a thymus and receives mediastinal irradiation. Here we evaluate the effect of CsA and irradiation on the relative abundance of thymic dendritic cells (DC). DC were identified with an immunoperoxidase stain for ED1 and were quantified by computerized planimetry. Normal young rats have scattered DC in the cortex and numerous DC in the medulla with a concentration at the cortico-medullary junction. Short-term CsA induces a marked loss of medullary DC (798 +/- 126 cells/mm to 88 +/- 103, P less than 0.001) and a modest loss of cortical DC (543 +/- 55 to 330 +/- 130, P less than 0.01). While medullary DC normally recover promptly post-CsA, rats receiving mediastinal irradiation demonstrated minimal recovery post-CsA (P less than 0.0003). The prolonged deficiency of medullary DC could represent an essential early step for loss of self-tolerance and sGVHD.

Flow cytometric analysis of lymphocyte subpopulations in the spleen and thymus of mice exposed to an acute immunosuppressive dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The objective of the present studies was to determine if acute exposure to an immunotoxic dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces alterations in the expression of lymphocyte surface markers as measured by multiparameter flow cytometry. The immunotoxicity of a single oral dose of TCDD was assessed by the anti-SRBC PFC response; an ED50 of 0.74 micrograms/kg was determined. Subpopulations in the spleen and thymus of C57B1/6 mice were analyzed 2 days following exposure to 2 micrograms/kg TCDD. In addition, splenic lymphocyte subsets were examined on Days 1-4 following SRBC challenge of mice treated with 0, 2, or 5 micrograms/kg TCDD. T and B cells were identified by single parameter analysis of Thy 1.2 and Ig expression. T cell subsets were defined by dual parameter analysis of CD4 and CD8 expression. In TCDD-treated mice, the percentage and the total number of double-positive CD4+ CD8+ thymocytes were significantly decreased while the percentage but not the total number of double-negative CD4- CD8- thymocytes was significantly increased. No changes in the percentage or total number of single positive (CD4+ CD8- or CD4- CD8+) thymocyte subsets were observed. In contrast to the thymus, lymphocyte subsets in the spleen were not significantly altered in percentage or total number 2 days following acute TCDD exposure. When splenic lymphocytes were analyzed daily following SRBC challenge, Ig+, Thy 1.2+, and CD4+ CD8- subpopulations remained relatively unchanged in both control and TCDD-treated animals. A small but significant decrease in the percentage of CD4- CD8+ T cells was observed on Day 3 in mice treated with 2 or 5 micrograms/kg TCDD when compared to that of vehicle-treated mice. The total number of CD4- CD8+ splenocytes was also significantly lower in the 5-micrograms/kg group on Day 3. However, this effect appeared to result from an elevation of the CD4- CD8+ subset in the controls rather than from a reduction in the TCDD-treated groups. Double-positive (CD4+ CD8+) lymphocytes were not detected in either control or TCDD-treated spleens. These results indicate that an acute dose of TCDD which reduced the splenic anti-SRBC response by 65-80% did not cause detectable changes in major splenic lymphocyte subpopulations. This is an important finding from the standpoint of utilizing lymphocyte subset analysis to screen for potential immunotoxic effects of TCDD. Specifically, the absence of subset changes does not preclude the presence of functional immunosuppression.