Recovery from chemically induced thymus atrophy starts with CD4- CD8- CD2high TcR alpha beta-/low thymocytes and results in an increased formation of CD4- CD8- TcR alpha beta high thymocytes.

Regeneration of the thymus was studied in rats that were treated with a single oral dose of the organotin compound di-n-butyltin dichloride (DBTC). After an initial maximum depletion of cortical BrdU+ thymocytes on day 2 after treatment, repopulation appeared to start on day 3 as indicated by an increased number of BrdU+ cells in the subcapsular region. On day 5, when thymocyte depletion was most pronounced, a relative increase of BrdU+ cells was observed all over the cortex. In comparison with controls, the thymoblast population on day 5 appeared to harbour increased numbers of CD4- CD8- and immature CD4- CD8+ CD53- thymoblasts, while the number of CD4+ CD8+ blasts had decreased. In comparison with day 3, however, the number of CD4+ CD8+ blasts had increased again. Results together have been interpreted as indicative for thymus regeneration starting from CD4- CD8- blasts which differentiate to immature CD4- CD8+ and then to CD4+ CD8+ blasts. Further characterization revealed that the majority of the CD4- CD8- and CD4- CD8+ CD53- blasts expressed high levels of CD2 and no or low levels of T-cell receptor (TcR) alpha beta. The high expression of CD2 on repopulating thymoblasts may be an additional indication of their activated state and for a role of interaction with the ligand LFA-3 on thymic epithelial cells during this phase of thymocyte differentiation. The number of CD4- CD8- TcR alpha beta high cells was increased on day 5 after dosing. The origin of this population and the possible implication of its development during thymus regeneration after chemically induced thymus atrophy are discussed.

The organotin-induced thymus atrophy, characterized by depletion of CD4+ CD8+ thymocytes, is preceded by a reduction of the immature CD4- CD8+ TcR alpha beta-/low CD2high thymoblast subset.

Thymic changes in the rat induced by the thymus atrophy-inducing organotin compound di-n-butyltin dichloride (DBTC) were examined using FACS analyses. The number of CD4+CD8+ thymocytes was reduced by DBTC treatment from Day 2 onwards and reached minimum level on Days 4 and 5 after dosing. On these days the CD4-CD8- and both the CD4-CD8+ and CD4+CD8- subsets were not affected. On Day 2 we observed a reduced proportion of transferrin receptor (CD71)-positive CD4-OX44- cells, representing the cycling immature CD4-CD8+ cells, and of CD71+OX44- cells, representing the cycling CD4+CD8+ cells, but not of CD71+CD4-CD8- cells. When compared to controls, the FSChigh cell population of DBTC-treated rats contained less CD4-OX44- and OX44- cells, which were further characterized as CD2high and T-cell receptor (TcR)alpha beta- low. Moreover, fewer TcR alpha beta high cells were detected in the OX44- thymoblast subset of DBTC-treated rats. The number of CD4-CD8- thymoblasts appeared marginally decreased while the numbers of CD4+OX44+ cells, representing mature CD4+ cells, were not affected. These data indicate that DBTC causes a preferential initial depletion of immature CD4-CD8+CD2high TcR alpha beta-low thymoblasts. This initial event may result in a decreased formation of CD4+CD8+ thymoblasts and of small CD4+CD8+ thymocytes. These characteristics of the initially depleted subset indicate a specific anti-proliferative effect of DBTC and may give clues for the mechanism involved in the induction of thymus atrophy.

Effects of the color additive caramel color III and 2-acetyl-4(5)-tetrahydroxybutylimidazole (THI) on the immune system of rats.

Administration of ammonia caramel color (AC) to rats may decrease blood lymphocyte counts, specifically in rats fed a diet low in vitamin B6. This effect is associated with 2-acetyl-4(5)-(1,2,3,4-tetrahydroxybutyl)imidazole (THI). To characterize and compare the effects of AC and THI and to study the influence of dietary pyridoxine, two studies in rats were conducted. Weanling rats fed a diet containing 2-3 ppm pyridoxine and exposed to 4% AC or 5.72 ppm THI in drinking water for 4 weeks showed reduced cell numbers in spleen and popliteal lymph nodes, as well as in the blood. Flow cytometric analyses demonstrated a comparable reduction in B and T lymphocytes. In blood, spleen, and popliteal lymph nodes, CD4+ lymphocytes were more reduced than CD8+ cells. The number of bone marrow cells was not affected. Although thymus weight and cell number were not affected either, a decreased cortex over medulla area ratio and an increase in medullary cell density largely due to an increase in CD4+ thymocytes was observed. Decreased numbers of ED2+ macrophages were observed in the thymic cortex and in the spleen red pulp. All effects observed were either less pronounced or absent in a study with rats fed a diet containing 11-12 ppm pyridoxine. The effects of AC and THI on the immune system were similar. Whereas AC exposure was associated with changes in vitamin B6 status, THI did not induce obvious effects on vitamin B6 parameters. It is proposed that the effects of AC and THI on the immune system are not caused by a disturbance of vitamin B6 metabolism, but may in fact result from a disturbance of a specific PLP-dependent process.

Organotin-induced thymus atrophy concerns the OX-44+ immature thymocytes. Relation to the interaction between early thymocytes and thymic epithelial cells?

After single oral application of the organotin compound di-n-butyltindichloride (DBTC) to rats, a reversible dose-dependent thymus weight reduction is observed. This is maximal at day 4 and recovers to the control value approximately at day 9 after administration. In this study the changes in thymocyte subpopulations after a single oral dose of 15 mg DBTC/kg body weight were analysed by immunohistology. Thymus glands of exposed rats were collected at day 1,2,3,4,5,7 and 9 after DBTC dosing and frozen sections were screened for various thymocyte differentiation antigens. Staining by mAb HIS-44 that labels a subset of cortical thymocytes showed that the thymus atrophy was restricted to the cortex. Here a time-dependent decrease of labelling by CD2 (OX-34), CD8 (OX-8), CD4 (ER-2), and CD5 (OX-19) was observed. In contrast, the number of cortical OX-44+ cells increased from day 2 to day 5. This increase can reflect an increase of CD4-CD8- double-negative thymocytes or of macrophages. However, most of these OX-44+ cells were negative for acid phosphatase, which is present in most macrophages. We concluded that these OX-44+ cells were mainly CD4-CD8- thymocytes and that the thymocyte subpopulation of this phenotype, i.e. CD4-CD8-OX-44+, may be the target cell for DBTC. It is discussed whether DBTC might disturb the interaction of early thymocytes and thymic epithelium, probably by an interaction with the CD2 antigen.

Immunophenotyping of non-Hodgkin's lymphoma. Lack of correlation between immunophenotype and cell morphology.

The establishment of Clusters of Differentiation for T- and B-lymphoid cells during International Workshops on Human Leukocyte Differentiation Antigens prompted the authors to evaluate the immunophenotypes in 160 cases of non-Hodgkin's lymphoma (NHL). In this group, 130 were of B-lymphocyte lineage (117 by monotypic immunoglobulin expression), and 30 of T-cell lineage. In the B-NHL series the expression of immunoglobulin isotypes, B-cell maturation/differentiation antigens of CD9, CD10, CD19-24, CD37, and CD38 (OKT10), HLA-DR and peanut agglutinin binding showed no significant relationship with histopathologic diagnosis as defined by the Kiel classification. Of the T-cell markers, CD5, CD6, and CD7 showed lineage promiscuity by their presence on some B-NHL. Conversely, the authors grouped the cases according to phenotypes (either CD antigens or immunoglobulin isotypes) which occur in distinct stages of (physiologic) B-cell maturation/differentiation. Eighty-six of the 130 cases could be fitted according to CD phenotype expression. This approach did not yield a significant relationship between phenotype and individual histopathologic categories either. The staging by CD phenotype and by immunoglobulin isotype yielded different results in this respect. Most B-NHL had an intermediate stage of B-cell maturation/differentiation. In the T-NHL series most cases showed a phenotype (CD1-CD8, CD38, TdT, and peanut agglutinin binding capacity) compatible with mature T-lymphocyte characteristics. The exceptions were lymphoblastic convoluted lymphomas, which exhibited an immature immunophenotype. It is concluded that NHL in distinct histopathologic categories are heterogeneous in immunologic phenotypes, and that the immunophenotype of lymphoma cells has no evident association with that of their presumed counterparts in physiologic cell maturation/differentiation.