Essential dynamics of DNA containing a cis.syn cyclobutane thymine dimer lesion

Conformational properties of a UV-damaged DNA decamer containing a cis.syn cyclobutane thymine dimer (PD) have been investigated by molecular dynamics (MD) simulations. Results from MD simulations of the damaged decamer DNA show a kink of approximately 21.7 degrees at the PD damaged site and a disruption of H bonding between the 5'-thymine of the PD and its complementary adenine. However, no extra-helical flipping of the 3'-adenine complementary to the PD was observed. Comparison to two undamaged DNA decamers, one with the same sequence and the other with an AT replacing the TT sequence, indicates that these properties are specific to the damaged DNA. Essential dynamics (ED) derived from the MD trajectories of the three DNAs show that the backbone phosphate between the two adenines complementary to the PD of the damaged DNA has considerably larger mobility than the rest of the molecule and occurs only in the damaged DNA. As observed in the crystal structure of T4 endonuclease V in a complex with the damaged DNA, the interaction of the enzyme with the damaged DNA can lead to bending along the flexible joint and to induction of adenine flipping into an extra-helical position. Such motions may play an important role in damage recognition by repair enzymes.

Weak association between retinopathy of prematurity and neurological disorders in childhood

An attempt was made to elucidate the association between retinopathy of prematurity (ROP) and neurological disorders in infants of very low birth weight. In this retrospective study, 1081 Japanese children weighing less than 1500 g at birth were classified into four subgroups according to birth weight. In each subgroup, the association among cerebral palsy (CP) or mental retardation (MR) and ROP, treated ROP, and cicatricial ROP was analyzed statistically. In the population as a whole, CP and MR were positively associated with ROP. However, in the birth weight subgroup analysis, no significant association was found. We can conclude that there is a weak association between ROP and CP or MR.

Serum levels of soluble interleukin-2 receptor in renal cell carcinoma

OBJECTIVES

To evaluate increased serum soluble interleukin-2 receptor (sIL-2R) levels in patients with renal cell carcinoma (RCC).

METHODS

Serum sIL-2R levels were measured in 52 patients with RCC and 10 control subjects by an enzyme-linked immunosorbent assay (ELISA) technique. The correlation between serum sIL-2R levels and clinical stage, disease prognostic value, and inflammatory marker levels was analyzed.

RESULTS

Serum sIL-2R levels in patients with RCC were significantly higher than those in normal control subjects (857.2 +/- 660.0 versus 291.3 +/- 76.4 U/mL, P < 0.0001). High serum sIL-2R levels appeared to be related to advanced clinical stage (596.0 +/- 276.5 U/mL in Stage II, 776.1 +/- 398.8 U/mL in Stage III, and 1310.0 +/- 926.7 U/mL in Stage IV: Stage II vs. Stage III, P = 0.0078; Stage II vs. Stage IV, P < 0.0001). The overall cause-specific survival curves showed that patients with high sIL-2R levels (more than 1000 U/mL) had a significantly lower survival rate than those with low (less than 500 U/mL, P = 0.0003) or intermediate levels (500 to 1000 U/mL, P = 0.0007). C-reactive protein levels apparently increased in patients with high sIL-2R concentrations.

CONCLUSIONS

Measurement of serum sIL-2R concentrations in patients with RCC provides useful information for predicting the extent of disease and length of survival.

Ophthalmic findings in a case of hemophagocytic syndrome

PURPOSE

To report a case of hemophagocytic syndrome, which is characterized by hemophagocytosis of histiocytes; optic nerve involvement, and unusual retinal white patches.

METHOD

Case report. A 10-year-old boy had repeated relapses of hemophagocytic syndrome. He complained of swelling of the right upper eyelid and bilateral visual disturbance.

RESULTS

Ophthalmoscopic examination disclosed bilateral optic disk edema, retinal hemorrhages, and multiple perivenous white patches in the retina. Magnetic resonance imaging demonstrated enlargement of both optic nerves. After chemotherapy and bone marrow transplantation, his visual acuity improved in both eyes, and retinal patches changed to inactive-appearing scars.

CONCLUSION

Hemophagocytic syndrome may manifest with ophthalmic findings such as optic nerve involvement, retinal hemorrhages, and multiple white perivenous retinal patches.

Metabolism of the intravenously administered recombinant human basic fibroblast growth factor, trafermin, in liver and kidney: degradation implicated in its selective localization to the fenestrated type microvasculatures

The fate of trafermin (recombinant human basic fibroblast growth factor) was examined after intravenous administration of its iodinated form to rats. Autoradiography at 5 and 30 min after the injection showed that 125I-trafermin is localized specifically in the fenestrated endothelium through binding to heparan sulfate proteoglycans (HSPG) in liver, kidney, adrenal, spleen, hypophysis and bone marrow. Metabolites in the organs were examined at 5 min and 24 h after the injection. More than 73% of radioactivity in liver and kidney was extractable at either time point, and a large majority of the extracted radioactivity was heparin-binding. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed that the substantial radioactivity recovered from liver and kidney can commonly be attributed to a peptide with the same molecular weight as the intact trafermin (B-1, 17.7 kDa) and only three truncated metabolites (B-2, 15.0 kDa; B-3, 7.2 kDa; B-4, 4.2 kDa). Because no truncated metabolites were found in serum, these metabolites seem to be produced inherently in liver and kidney. Although they all retained heparin-binding capacity, only B-1 and B-2 exhibited a stimulatory effect on proliferation of endothelial cells, and these bioactive peptides disappeared completely from liver within a day, indicating a rapid inactivation process in the organs. Taken together with the morphological evidence on autoradiography, it seems most likely that the injected trafermin could be inactivated in sinusoidal endothelial cells, probably through a well-known internalization mechanism of the basic fibroblast growth factor-HSPG complex.

Molecular cloning of sheep and goat ferredoxin reductase messenger ribonucleic acids, and identification of an alternatively spliced form of sheep ferredoxin reductase

Complementary DNA clones of mRNAs for sheep and goat NADPH-ferredoxin reductases (ferredoxin NADP+ oxidoreductase, EC 1.18.1.2) were isolated by the reverse transcriptase polymerase chain reaction method, and the complete nucleotide sequences of the coding and 3'-flanking regions of these cDNA clones were determined. Comparative analysis using the deduced amino acid sequences of NADPH-ferredoxin reductases clarified the interspecific conservation of the ferredoxin-binding and flavin adenine dinucleotide (FAD)-binding regions, confirming the results reported previously. During this study, we happened to identify an alternatively spliced mRNA that completely lacks exon 3, just adjacent to the FAD-binding region of the sheep NADPH-ferredoxin reductase cDNA clone. In the screening of other alternatively spliced mRNAs of NADPH-ferredoxin reductases derived from several steroidogenic organs, such as adrenocortices, testes, and ovaries of sheep and goats, only one kind of alternatively spliced mRNA as described above was detected in sheep adrenocortices. Then, we constructed Escherichia coli expression systems for these two forms of mRNA and analyzed their enzymatic properties. We found that the ability of the alternatively spliced NADPH-ferredoxin reductase protein to transfer electrons to ferredoxin is completely abolished because FAD binding is inhibited.

No linkage of the cytochrome P-450IIE1 (CYP2E1) C1/C2 polymorphism to schizophrenia

We investigated, using PCR-SSCP analysis, the relationship between schizophrenia and the polymorphism of d-benzphetamine N-demethylase (cytochrome P-450j or CYP2E1), which metabolizes psychotropic substances such as d-benzphetamine and alcohols. Among 41 patients with schizophrenia, no statistically significant change in the frequency of the mutant (C2) allele relative to in controls was found, and no novel structural mutation in the CYP2E1 gene, which would be expected to alter the CYP2E1 protein, was found. This could be explained by no linkage of the CYP2E1 gene (mutations in the exon 1-9, and C1/C2 polymorphism) to schizophrenia.

Rhabdomyoma of the orbit in a child

PURPOSE

To study a case of rhabdomyoma of the orbit in a 16-month-old boy.

METHOD

The child had progressive right proptosis for 1 month. He underwent a computed tomographic scan, which showed an irregular right retrobulbar mass and partial resection.

RESULTS

Histologic examination disclosed well-differentiated striated muscle cells with a mixture of collagen fibers and immature striated muscle cells with centrally placed nuclei. The specimen lacked nuclear atypia, indicating benign rhabdomyoma of the orbit. During the 1 1/2-year follow-up, the patient did not receive additional treatment, and no regrowth occurred.

CONCLUSION

Rhabdomyoma can occur in the orbit of a child. Because of differences in treatment, rhabdomyoma must be distinguished from rhabdomyosarcoma.

Tissue-specific alternative splicing of mouse brain type ryanodine receptor/calcium release channel mRNA

We detected alternative splicing of the mouse brain type ryanodine receptor (RyR3) mRNA. The splicing variant was located in the transmembrane segment. The non-splicing type (RyR3-II) included a stretch of 341 bp, and that of the 13th codon was stop codon TAA. Reverse transcription-polymerase chain reaction (RT-PCR) analysis shows that RyR3-II mRNA was expressed in various peripheral tissues and brain at all developmental stages. However, interestingly, the splicing type (RyR3-I) mRNA was detected only in the cerebrum. These findings suggest that the splicing variants RyR3-I and RyR3-II may generate functional differences of RyR3 in a tissue-specific manner.

[Dynamic Gd-DTPA-enhanced MR imaging in evaluation of the function of transplanted kidneys]

The purpose of the study was to evaluate the potential of dynamic Gd-DTPA-enhanced MR imaging in assessing of the function of transplanted kidneys. Dynamic MR imaging was performed using the GRASS pulse sequence in 21 subjects (56 examinations), and in each examination 30 images were obtained after a bolus injection of Gd-DTPA. Imaging findings including signal increase and/or signal drop in cortex, signal drop in medulla, and signal drop in calyces were utilized for the evaluation of renal function. Renal function was also evaluated using the following parameters: Ta, time between the initial observation of signal increase in cortex and signal drop in medulla. Tb, time between the initial observation of signal drop in medulla and in calyces; Tc, Ta + Tb, and Max. C/M, maximum ratio of signal intensity between cortex and medulla among 30 images. In the group of patients with normal graft function (Ccr > or = 60ml/min), all imaging findings were observed. In the group of patients with mild graft dysfunction (30ml/min < or = Ccr < 60ml/min), all imaging findings but signal drop in cortex were observed. The time parameters of Ta, Tb, and Tc were significantly larger, and Max. C/M was significantly smaller than those observed in the group with normal graft function. In the group of patients with severe graft dysfunction (Ccr < 30ml/min), almost none of the findings were observed. The investigation in patients in the postoperative state revealed a close correlation of the imaging findings and the values of parameters with changes in graft function over time. The results indicated the usefulness of the method in semiquantitative evaluation of graft function, including that of patients in postoperative state. This study suggests that dynamic Gd-DTPA-enhanced MR imaging could be a valuable method for the management of transplanted kidneys.

Development of functional rat-derived T cells in SCID mice engrafted with the fetal thymus of LEC rats which are defective in CD4+ T cells

We reported that LEC rats are genetically deficient in the development of thymic CD4+8- cells and that this defect is caused by bone marrow (BM)-derived stem cells. To determine which BM-derived cells are responsible for the arrest of T-cell development in LEC rats, fetal thymuses of LEC rats, or LEA rats which bear the same major histocompatibility complex (MHC) as LEC rats but are immunologically normal, were engrafted under the kidney capsule of severe combined immunodeficiency (SCID) mice (LEC-TG and LEA-TG mice, respectively). We than examined the differentiation of T cells and their immunological functions in the SCID mice. A large number of rat-derived CD4+ T cells appeared in the peripheral blood, lymph nodes (LN) and spleens in LEC-TG mice. Furthermore, the peripheral LN cells in LEC-TG mice appeared to be functional. These cells produced IL-2 upon Con A stimulation, whereas LN cells from LEC rats produced no IL-2 in the same conditions. Thymopoiesis was observed at 3 weeks in LEC-TG as well as LEA-TG mice. The distribution of thymocyte subsets with respect to CD4 and CD8 expression in LEC-TG mice closely resembled that of LEA rat thymus and that in LEA-TG mice, suggesting that normal T-cell differentiation occurred in LEC-TG mice. The results indicated that BM-derived progenitor T cells of LEC rats could differentiate to functional CD4+ T cells.

Antigen-specific B cells are required for the secondary response of T cells but not for their priming

We studied the potential role of B cells in T cell responses using severe-combined immunodeficient (SCID) mice grafted with the thymus from fetal C.B-17 mice (TG mice). These mice developed both CD4+ and CD8+ T cells, but not B cells within 2 months after transplantation. TG mice showed normal delayed-type hypersensitivity responses against the immunizing antigen ovalbumin (OVA). Lymph node (LN) cells of TG mice proliferated well in response to concanavalin A (Con A). Further, Con A stimulation induced the production of interleukin (IL)-2, IL-6 and interferon (IFN)-gamma and the expression of IL-4 mRNA. Thus, TG mice were reconstituted without remarkable immunodeficiency. However, these T cells failed to proliferate to OVA stimulation. Response to OVA was also inhibited in SCID mice grafted with fetal C.B-17 liver cells when B cells were depleted in the proliferation assay. Unresponsiveness against immunizing antigen was restored by the addition of antigen-primed B cells, but not by naive B cells, lipopolysaccharide-activated B cells or B cells primed with sheep red blood cells. Next, we examined whether antigen-primed B cells could induce T cell responses without professional antigen-presenting cells (APC). T and B cells were purified from OVA-immunized mice by cell sorter. These T cells proliferated in response to OVA and produced IFN-gamma in the absence of non-B APC. When anti-CD80 or anti-CD86 was added in the assay, proliferation and IFN-gamma production was inhibited. These results indicate that B cells activated specifically with antigen are required for the secondary response of T cells, but not for their priming.

[A preliminary study of percutaneous ethanol injection therapy for hepatocellular carcinoma: evaluation of the ethanol diffusion area by the ethanol mixed with gadolinium]

To evaluate the ethanol diffusion area after Lipoidalization in 3 patients with advanced HCC treated by Lipoidalization-PEIT combination therapy, 99.9% ethanol mixed with Gadolinium was used for PEIT (Gd-PEIT). T1-weighted MR images wear obtained 1 hr after Gd-PEIT. The area of homogeneous hyperintense change on T1-weighted MR images was taken to be the ethanol diffusion area. In all 3 patients, homogeneous hyperintensity throughout the tumor over the capsule was recognized on T1-weighted MR images after treatment. The results suggests that T1-weighted MR images after Gd-PEIT provide a valuable tool by which to directly evaluate the ethanol diffusion area for advanced HCC treated by Lipoidalization followed by PEIT.

[Evaluation of renal function using Gd-DTPA dynamic MR imaging]

To establish a new method for evaluating renal function using MRI, we performed dynamic Gd-DTPA enhanced MR imaging at 1.5 T in 68 subjects (71 examinations), including 23 normal volunteers, 19 patients with chronic renal failure, 22 with hydronephrosis, and 7 with renal vascular disorders. Thirty GRASS images [35/9/20 degrees /1 (TR/TE/Flip Angle/NEX)] were obtained after a bolus injection of Gd-DTPA (0.2 mmol/Kg) in each case, and were evaluated in the following respects. (1) Whether or not the initial signal increase and/or the following signal drop in cortex was observed. (2) Whether or not the signal drop in medulla and/or calyces was observed. (3) Time between initial signal increase in cortex and signal drop in medulla (Ta). (4) Time between signal drop in medulla and calyces (Tb). (5) Time between signal increase in cortex and signal drop in calyces (Tc). (6) Maximum ratio of signal intensity between cortex and medulla (Max. C/M). In normal subjects, the initial signal increase and the following signal drop in cortex, and the signal drop in medulla and calyces were observed. In patients with abnormal renal function, the characteristic signal changes described above were not seen clearly or disappeared in many cases. In normal subjects, Ta, Tb, Tc, and Max. C/M were 41.9 +/- 6.9 sec, 53.2 +/- 10.6 sec, 95.0 +/- 9.5 sec, and 1.10 +/- 0.05, respectively. In the patients, time parameters were significantly larger than those of normal subjects and C/M ratios were lower. This study suggested that dynamic Gd-DTPA renal MR imaging can serve as a new method for the evaluation of renal function.

Molecular cloning and nucleotide sequences of cDNA clones of sheep and goat adrenocortical cytochromes P450scc (CYP11A1)

We isolated cDNA clones of the mRNAs for cytochromes P450scc (CYP11A1) from sheep and goat adrenocortices using the RT-PCR method. We determined the complete nucleotide sequences of the coding and 3'-flanking regions of these cDNA clones. The results confirmed the amino terminal sequence of the sheep cytochrome P450scc reported previously [Miyatake et al., Biochim. Biophys. Acta 1215,176-182 (1994)]. On the basis of comparison of the deduced amino acid sequences of various animals and rainbow trout cytochromes P450scc, and other mitochondrial cytochrome P450 isozymes, we discussed the substrate-associated and adreno-ferredoxin-binding region of cytochrome P450scc.

[Measurement of gastric emptying by magnetic resonance imaging]

The purpose of the study was to establish a new method of measuring gastric emptying using MR Imaging in human. Gastric emptying was measured in 6 healthy male volunteers aged from 28 to 43 years, using MR imaging and RI. The measurements were performed after the oral administration of liquid meal containing glucose, protein and fat. The MR imaging was performed with 0.5T superconducting magnet machine, and consecutive 12 transaxial T1 weighted spin echo images (TR/TE = 300/17) of the upper abdomen were recorded every 10 minutes for more than 1 hour. Gastric emptying curves and their T1/2 values obtained by MR imaging and RI method were correlated well in 5 of 6 cases. We concluded that a non invasive and radiation free method using MR imaging was proved to be a useful tool for measuring gastric emptying.

A fluorometric assay for measuring deamidase (lysosomal protective protein) using high-performance liquid chromatography

A rapid and sensitive assay method for the determination of deamidase activity is reported. This method is based on fluorometric detection of a dansylated dipeptide, 5-dimethylaminonaphthalene-1-sulfonyl-D-Tyr-Val (N-Dns-D-Tyr-Val), enzymatically formed from the substrate 5-dimethylaminonaphthalene-1-sulfonyl-D-Tyr-Val-NH2 (N-Dns-D-Tyr-Val-NH2), after separation by high-performance liquid chromatography (HPLC) using a C-18 reversed-phase column by isocratic elution. This method is sensitive enough to measure N-Dns-D-Tyr-Val at concentrations as low as 100 fmol, yields highly reproducible results and requires less than 8.5 min per sample for separation and quantitation. The optimum pH for deamidase activity was 4.0-4.5. Greater than 5 mM of reduced glutathione was needed for maximal enzyme activity. The Km and Vmax values were respectively 125 microM and 14.12 pmol/micrograms/h with the use of enzyme extract obtained from mouse spleen. Deamidase activity was strongly inhibited by Ag+, Cu2+, diisopropylfluorophosphate, and p-chloromercuriphenylsulfonic acid. Among the organs examined in a mouse, the highest specific activity of the enzyme was found in spleen. The sensitivity and selectivity of this method will aid in efforts to examine the physiological role of this enzyme.

An interleukin-1 binding region oligopeptide from the human type I IL-1 receptor reduces acute inflammation, delayed hypersensitivity reaction, and lethal endotoxemia in animals

The effect of an interleukin-1 binding region oligopeptide from the interleukin-1 receptor on various inflammatory responses was investigated in animal models. A synthetic peptide (KICIRIQIS) corresponding to 86-93 of the extracellular domain of the human type I interleukin-1 receptor was used. Carrageenan-induced rat paw edema, a model of acute inflammation, was dose dependently suppressed by intraperitoneal administration of the peptide. The delayed hypersensitivity reaction to sheep red cells was diminished by pretreatment of mice with the peptide at a relatively high dose. In a murine lethal endotoxemia model, animals treated with the interleukin-1 receptor peptide (10 mg/kg x 4) showed significantly better survival than vehicle-treated animals when the peptide was administered from 20 minutes after lipopolysaccharide injection. Improved survival was accompanied by suppression of lipopolysaccharide-induced production of colony-stimulating factor, although the peptide did not improve hypoglycemia. These findings suggest that the interleukin-1 receptor peptide may be a potential treatment for various inflammatory processes.

Expression of CD44 splice variants in bladder cancer

BACKGROUND

Recently, it was noted that CD44 participates in a wide variety of cell-cell or cell-matrix interactions including tumor metastasis and the altered expression of CD44 splice variants is helpful in the diagnosis of colon and breast cancer. The purpose of the study was to investigate altered expression of CD44 in bladder cancer.

METHODS

Thirty-three surgical specimens of 22 patients and seven bladder cancer cell-lines were analyzed by various methods including RT-PCR-Southern blotting. Northern blotting, and flow-cytometric analysis.

RESULTS

In RT-PCR analysis, the hematopoietic variant and numerous additional variants were detected in all cell-lines and almost all surgical specimens. In three out of seven cell-lines of bladder cancer (42.9%), especially numerous larger bands (ladder pattern) were detected using RT-PCR. These three cell-lines expressed a smaller quantity of CD44 mRNAs and CD44 molecules than the other four cell-lines. In eighteen out of 22 (81.8%) bladder cancer specimens, we detected larger variants that exceed 1500 base pairs, compared with the detection in four out of eleven (36.4%) visually normal mucosa specimens (P < 0.05). However, there was no correlation between the expression of the larger variants and clinicopathological features.

CONCLUSION

The quantitative and qualitative change of CD44 variants were demonstrated in bladder cancer.

Establishment of a xenogeneic chimera without GVHD in NK cell-depleted SCID mice by grafting rat fetal liver cells

Rat lymphopoiesis did not develop when naive SCID mice were transplanted with rat fetal liver cells. However, when SCID mice were depleted of NK cells by administration of anti-murine IL-2R beta mAb before transplantation, remarkable reconstitution of both rat T and B cells was observed in these mice without any evidence of graft-versus-host disease macroscopically or histologically. T cells in these reconstituted mice proliferated well in response to Con A and third-party rat and mouse antigens, whereas no response was seen to the stimulation with either donor rat- or host mouse-type cells. When these xenogeneic chimera mice had been immunized with SRBC, these mice exhibited DTH reaction and antibody production against the homologous antigen. These results indicate that rat fetal liver cells can differentiate to functional T and B cells in the xenogeneic microenvironment of SCID mice, if host NK cells are depleted beforehand. These rat-type T cells develop within SCID thymuses and acquire tolerance to either donor F344 rat or host SCID mouse antigens.

Streptococcus oralis previously identified as uncommon 'Streptococcus sanguis' in Behçet's disease

The relation between the biochemical and serological properties of 'Streptococcus sanguis' was studied to characterize the strains isolated from dental plaque of patients with Behçet's disease and controls. Seven reference and 100 clinical strains preserved by the Behçet's Disease Research Committee of Japan were identified using established criteria and differentiated with antisera against Strep. oralis ATCC 10557, Strep. sanguis ATCC 10556 and 'Strep. sanguis' ST7, compatible with the criteria. Uncommon serovars (serotypes) KTH-1 (= ATCC 49298), KTH-2 (= ATCC 49296), KTH-3 (= ATCC KTH-4 (= ATCC 49297) and B220 (serovar KTH-1) with both IgA1 protease and neuraminidase (sialidase) were identified as Strep. oralis, whereas common serovars ST3 with IgA1 protease alone and ST7 without both enzymes were identified as Strep. sanguis and Strep. gordonii, respectively. Isolates previously ranked as uncommon serovars were identified as Strep. oralis, whereas the rest ranked as common serovars were identified as the same species as those of the grouping strains. A soft-agar technique was available for species identification except for Strep. oralis serovar KTH-1 reacting with the antiserum against Strep. gordonii ST7. The frequency of isolation of Strep. oralis was higher in Behçet's disease (52%) than in controls (38%), but no difference was observed between the properties of the two groups of isolates. Strep. oralis virulence factors may be involved in breach the mucosal barrier in patients with specific reactivity to these antigens and inducing Behçet's disease.

Split tolerance between spleen and lymph node cells in severe combined immunodeficiency mice grafted with AKR fetal liver cells

Severe combined immunodeficient (SCID) mice defective in stem cells for T and B cells appear to be an ideal host for construction of chimeric mice. When bone marrow cells are used as a source of stem cells, however, host SCID mice do not always show sufficient reconstitution. In this study, fetal liver cells from AKR embryos were transplanted into SCID mice without prior irradiation. This treatment induced full reconstitution of lymphopoiesis as evaluated by flow cytometry analysis and serum Ig production 2 months after transplantation. Thus, fetal liver cells seem to be a better source for reconstitution of SCID mice than bone marrow cells. Lymph node (LN) cells of these mice (FLT mice) had no proliferative or cytotoxic activities against either host-type (C.B-17) or donor-type (AKR) spleen cells. However, spleen cells from FLT mice exhibited marked proliferative and cytotoxic activities against C.B-17 cells, with no activities against AKR cells. Split tolerance against C.B-17 cells in spleen and LN cells was not a transient phenomenon, since similar results were obtained from a cytotoxic T lymphocyte assay 4 months later. In spite of the strong host reactivity in vitro, aberration of clonal deletion or development of a graft-versus-host disease was not seen in FLT mice. As IL-2 induced the host reactivity of LN cells in a mixed lymphocyte reaction, potentially host-reactive T cells were present in LN but were rendered anergic. Tolerance in FLT mice seems to be regulated by a peripheral mechanism. We supposed that the split tolerance in FLT mice was induced by the different antigenicity between the spleen and LN.