The importation of hematogenous precursors by the thymus is a gated phenomenon in normal adult mice.

Hematogenous precursors repopulate the thymus of normal adult mice, but it is not known whether this process is continuous or intermittent. Here, two approaches were used to demonstrate that the importation of prothymocytes in adult life is a gated phenomenon. In the first, age-dependent receptivity to thymic chimerism was studied in nonirradiated Ly 5 congenic mice by quantitative intrathymic and intravenous bone marrow (BM) adoptive transfer assays. In the second, the kinetics of importation of blood-borne prothymocytes was determined by timed separation of parabiotic mice. The results showed that >60% of 3-18-wk-old mice developed thymic chimerism after intrathymic injection of BM cells, and that the levels of chimerism (range, 5-90% donor-origin cells) varied cyclically (periodicity, 3 to 5 wk). In contrast, only 11-14% of intravenously injected recipients became chimeric, and chimerism occurred intermittently (receptive period approximately 1 wk; refractory period approximately 3 wk). In the intravenously injected mice, chimerism occurred simultaneously in both thymic lobes; gate opening occurred only after most intrathymic niches for prothymocytes had emptied; and the ensuing wave of thymocytopoiesis encompassed two periods of gating. These kinetics were confirmed in parabiotic mice, and in cohorts of mice in whom gating was synchronized by an initial intrathymic injection of BM cells. In addition, a protocol was developed by which sequential intravenous injections of BM cells over a 3 to 4 wk period routinely induces thymic chimerism in the apparent absence of stem cell chimerism. Hence, the results not only provide a new paradigm for the regulation of prothymocyte importation during adult life, but may also have applied implications for the selective induction of thymocytopoiesis in nonmyeloablated hosts.

Association of immunophenotype with cerebrospinal fluid involvement in childhood B-lineage acute lymphoblastic leukemia.

The records of 71 pediatric patients who had B-lineage acute lymphoblastic leukemia (ALL) were studied retrospectively to document the correlation between antigenic phenotype of leukemic blasts in bone marrow (BM) and cerebrospinal fluid (CSF) involvement. Immunofluorescence assay for terminal deoxynucleotidyl transferase (TdT-IF) was used to examine specimens of CSF for the presence (CSF+) or absence (CSF-) of leukemic blasts at diagnosis and at various times after the induction of chemotherapy. The results of immunophenotyping of the leukemic blasts in the BM of the CSF+ and CSF patient groups were then compared, and the relative risk ratio and positive predictive value were calculated for each marker. In addition, other possible prognostic factors, such as gender, race and ethnicity, age, and initial leukocyte count were compared between the two groups. Thirty-eight percent of all patients, including those who had cytologically confirmed cases of CNS leukemia, had TdT+ cells in the CSF at diagnosis or during the course of the disease. No differences were observed between the CSF+ and CSF- groups with respect to clinical and demographic factors. However, the cases of CSF+ leukemia had the almost exclusive expression of cytoplasmic immunoglobulin heavy chain (c mu) or surface CD22 (Leu-14), CD23 (B6), and/or IgM markers, which normally characterize the most developmentally mature members of the B-cell series in BM. The expression of any of these antigenic markers at diagnosis appears to identify at least 88% of cases of B-lineage ALL that have or ultimately may have TdT+ cells in CSE The results of this study therefore may have both basic and clinical implications: The former concerns the mechanisms by which these phenotypically defined forms of ALL invade and persist in the CNS; the latter concerns the utility of routine immunophenotyping of BM blasts at diagnosis to assess the biologic predisposition to CNS involvement in individual cases of ALL.

Thymocytopoiesis is maintained by blood-borne precursors throughout postnatal life. A study in parabiotic mice.

This study was designed to resolve the long standing controversy as to whether hematogenous precursors or resident intrathymic precursors maintain thymocytopoiesis in postnatal life. The kinetics of thymic chimerism was examined over a 21-wk period in 105 pairs of nonirradiated, Thy-1-alloantigen-disparate, parabiotic B10.S mice. Thymic chimerism reached reached maximum levels of 25% in the Thy-1b and 16% in the Thy-1a partners (mean 20.5% and 9.8%, respectively) 6 to 7 wk after parabiotic union. Most of the donor-origin thymocytes were located in the thymus cortex and expressed high levels of Thy-1 Ag and terminal deoxynucleotidyl transferase. Thymic chimerism did not reach 50% because circulating prothymocytes, unlike peripheral T cells, do not distribute randomly in the blood of parabiotic partners. This was shown in irradiated pairs of Thy-1-alloantigen-identical parabiotic mice, one member of which was injected i.v. with Thy-1-alloantigen-disparate bone marrow cells. Only 10% of the total donor-origin prothymocyte activity was detected in the opposite parabiont 72 h later. Similarly, the level of thymic chimerism in nonirradiated, Thy-1-alloantigen-disparate parabionts closely corresponded to the donor: host ratio of prothymocytes in the blood (i.e., between 10 and 20%), as determined directly by an intrathymic adoptive transfer assay. The continued dependence of thymic chimerism on blood-borne precursors was formally demonstrated by surgically separating mice 9 wk after parabiosis. Twelve weeks later, thymic chimerism was 50 to 80% lower in the separated parabionts than in sham-operated controls. The possible role of "stress" in initiating or maintaining thymic chimerism during parabiosis appeared to be excluded by the existence of similar kinetics of thymocytopoiesis (including the onset of thymic involution) in parabiotic and nonparabiotic mice; and by the occurrence of similar levels of thymic chimerism in adrenalectomized and nonadrenalectomized parabiotic mice. Thus these experiments demonstrate that the maintenance of thymocytopoiesis in postnatal life, as in prenatal life, is primarily dependent upon blood-borne prothymocytes, and that intrathymic precursors are replaced at an average rate of 2 to 3%/day.

Studies of an L-rod sublaminar wire spinal fusion.

The spine of a 25-year-old man with Duchenne muscular dystrophy was studied postmortem, 8 years after spine fusion with L-rods and sublaminar wires. The fusion was solid. Instrumentation appeared to have had no adverse effects on the spinal cord or meninges or in the epidural space. When wire removal from the spinal canal and fusion mass was studied, increased penetration of the wires into the spinal canal was noted.

Hepatic toxicity of nickel chloride in rats.

Enhanced lipid peroxidation was observed in livers of rats killed 24 hr after sc injection of nickel chloride (NiCl2) (750 mumol per kg), as evidenced by 13-fold increase of conjugated dienes in microsomal lipids and 4-fold increase of thiobarbituric acid (TBA) chromogens in hepatic cytosol. Histologic examination of livers from rats killed one to three days after NiCl2 injection (500 mumol per kg) showed microvesicular fatty metamorphosis, mild hydropic degeneration, and foci of inflammation. Microvesicular steatosis of hepatocytes was confirmed by electron microscopy. Dose-related increases of serum aspartate aminotransferase (ALT) activity (up to 7-fold vs controls) and alanine aminotransferase (ALT) activity (up to 3-fold vs controls) were observed 24 hr after injection of NiCl2 (125 to 750 mumol per kg); diminished serum alkaline phosphatase activity (up to 72 percent reduction vs controls) was seen at NiCl2 dosages from 375 to 750 mumol per kg. Diethyldithiocarbamate did not influence the effects of NiCl2 on TBA-chromogens in liver homogenates or on serum AST and ALT activities but acted synergistically with NiCl2 to diminish serum alkaline phosphatase activity and to increase serum bilirubin concentration. This study demonstrates that parenteral administration of NiCl2 to rats produces acute hepatic toxicity, with enhanced lipid peroxidation, microvesicular steatosis, and increased serum AST and ALT activities.

Use of terminal deoxynucleotidyl transferase in the diagnosis of leukemia.

Terminal deoxynucleotidyl transferase (TdT) was determined by immunofluorescence in 30 patients with leukemia. In acute lymphocytic leukemia the proportion of cells positive for TdT was 19 to 77 percent during relapse (12 cases) and less than one percent during remission (three cases). In seven cases of myeloproliferative disease and two cases of lymphoma, the TdT was less than one percent. In one case of generalized lymphoblastic lymphoma and five cases of chronic myelocytic leukemia with "lymphoblastic" crisis, the cells positive for TdT were moderately increased. The presence of TdT in blast cells appears to have diagnostic, therapeutic, and prognostic significance.