Visceral Fat Accumulation Is Associated with Mild Cognitive Impairment in Community-Dwelling Older Japanese Women

OBJECTIVES

Visceral fat accumulation is detrimental for brain health and is associated with cognitive impairment in older adults. The objectives of the present study were to examine the association between visceral fat accumulation and prevalence of mild cognitive impairment and its subtypes.

DESIGN

a cross-sectional study.

PARTICIPANTS

This study enrolled 6,109 community-dwelling older adults, including 3,434 women (mean age: 74.4 years) and 2,675 men (mean age: 74.3 years). Individuals with dementia, Parkinson's disease, stroke, Mini-Mental State Examination scores ≤23, and who could not perform basic activities of daily living independently were excluded.

MEASUREMENTS

Participants underwent neurocognitive assessments to assess mild cognitive impairment (MCI) and its subtypes. Visceral fat area (VFA) was measured using abdominal bioelectrical impedance analysis. Participants were divided into quartile groups by VFA.

RESULTS

There were 731 (21.3%) women and 562 (21.0%) men with MCI, and the median VFA values were 63.3 cm2 and 96.3 cm2, respectively. Women participants in the second (adjusted odds ratios [aOR], 0.71; 95% confidence interval [95% CI], 0.54-0.94), third (aOR, 0.66; 95% CI, 0.47-0.92), and fourth quartiles of VFA (aOR, 0.62; 95% CI, 0.41-0.93) had a significantly lower risk of MCI than those in the first quartile. Higher VFA quartiles in women were associated with lower risk of non-amnestic MCI. There were no significant differences in men between quartiles.

CONCLUSIONS

Visceral fat accumulation was associated with MCI, especially non-amnestic MCI, in community-dwelling older Japanese women. These results suggest that visceral fat accumulation is partially protective against cognitive impairment.

309 PRODUCTION OF CATTLE BY NUCLEAR TRANSFER FROM CELLS IN WHICH A GENE IS DISRUPTED

Gene-targeted animals provide a powerful model to examine gene functionality. In this study, we examined the effect of gene targeting of donor cells for nuclear transfer (NT) on the pregnancy rate and on viability of the offspring after embryo transfer. Gene-targeted (tg; targeting of both alleles of the gene encoding bovine prion protein) or non-manipulated (control) bovine fetal fibroblasts were used for NT. A promoterless positive selection vector (pPrP5.2) containing an internal ribosome entry site-antibiotic resistance gene (neo) cassette and loxP sequences was used to disrupt the bovine prion protein gene. The cells (tg) in which homologous recombination was occurred were used for NT. The tg and control cells were cultured in DMEM with 10% FCS and were prepared in the early G1 phase to our previous report (Urakawa M et al. 2004 Theriogenology 62, 714–728). Each donor cell was inserted into an enucleated in vitro-matured (19 h) oocyte. Cell fusion (DC, 200 V mm–1, 10 μs) and activation (DC, 100 V mm–1 , 60 μs) were done in 0.3 m mannitol solution. The NT embryos were then activated with 5 μm Ca-ionophore and 10 μg of mL–1 cycloheximide and were cultured with bovine oviduct epithelial cells in CR1aa with 5% CS. The blastocyst rates were judged at 6 days after NT. The blastocysts were non-surgically transferred to recipient heifers. The recipients were monitored daily for heat behavior, examined by ultrasound at Day 30 and 60, and then observed monthly to confirm pregnancy. The offspring born in the tg group were confirmed by PCR to be transgenic. Statically significance was tested using a chi-square test or t-test. Developmental rate to the blastocyst stage, pregnancy rate at Day 30 and 60, and calving rate did not differ significantly between tg and the control group (Table 1). Gestation length (tg; 290.0 ± 2.2 days v. control; 290.5 ± 3.9 days) and birth weight (tg; 39.6 ± 8.0 kg v. control; 40.2 ± 4.1 kg) were not significantly different. These results indicate that gene targeting of donor cells used for NT does not significantly affect the development of embryos, pregnancy rate, or the viability of the offspring. Table 1.Development of NT embryos with tg or control cells

94 PRODUCTION OF AN α1,3-GALACTOSYLTRANSFERASE GENE KNOCKOUT CALF USING A SINGLE TARGETING VECTOR AND REJUVENATED CELL LINES

Gene targeting in large animals has the potential to be useful in agriculture. In this study, we examined whether an �1,3-galactosyltransferase-gene knockout (null) calf could be produced using a single targeting vector for disruption of both alleles and a rejuvenation of cell line by production of cloned fetuses. A promoter-less positive selection vector (pGT-22) containing an IRES (internal ribosome entry site)-antibiotic resistance gene(neo) cassette and loxP sequences was used to disrupt the bovine �1,3-galactosyltransferase (�1,3-GT) gene. In gene-targeting (GT), Japanese Black fetal fibroblasts were transfected with pGT-22, and were selected with 0.4 mg mL-1 G418. G418-resistant cells were monitored by PCR and Southern blot analysis. After PCR selection, a portion of the PCR-positive colonies were infected with the adenovirus AxCANCre, which transiently expresses Cre recombinase in the infected cells, to excise the antibiotic-resistance gene cassette (IRES/lacZ-neo) from the targeted allele. The targeted cells in which homologous recombination occurred were used for somatic cell nuclear transfer (SCNT). The cell cycle synchronization of donor cells in the early G1 phase and SCNT were performed according to the established procedure in our laboratory (Urakawa et al. 2004 Theriogenology 62, 714–728). As a result, in the first GT, one PCR-Southern blot-positive clone (0.26%, in 380 G418-resistant colony) was used for SCNT. Of 35 pulsed SCNT embryos, 4 (11.4%) developed to the blastocyst stage and 3 blastocysts were nonsurgically transferred to a recipient heifer; one fetus was recovered on Day 41. The cell line (�1,3-GT+/-) was established and was transfected with pGT-22 in the second GT. As a result, 8 PCR-Southern blot-positive clones (1.6%, in 508 G418-resistant colony) were recovered. The 2nd GT and the following SCNT were accomplished by the same methods used in the 1st GT and SCNT procedure. Of 36 pulsed SCNT embryos, 7 (19.4%) developed to the blastocyst stage and 3 blastocysts were nonsurgically transferred to a recipient heifer; one fetus was recovered on Day 41. The cell line (�1,3-GT-/-) was established, and was used for SCNT to obtain the �1,3-GT homozygous knockout offspring. Finally, 52 of 148 pulsed SCNT embryos (35.1%) developed to the blastocyst stage and 6 cloned embryos were transferred into 3 recipient heifers. A single knockout female offspring with normal morphology in all organs was born (Day 287) but died about one hour after birth. In this study, we established both heterozygous and homozygous �1,3-GT knockout cell lines from primary fetal fibroblasts and produced an �1,3-GT knockout offspring using a single targeting vector and rejuvenated cell lines.

72 EFFECT OF CELL CYCLE PHASE OF GENE-MANIPULATED FETAL FIBROBLASTS ON THE DEVELOPMENT OF CLONED BOVINE EMBRYOS

Transgenic bovine fetuses and offspring can be produced by using gene-modified somatic cells and clones of these cells. In this study, we examined the effects of specific cell cycle (early G1 phase) of donor cell (gene-manipulated fibroblasts) on the development of the nuclear transfer (NT) embryos into blastocysts and on the fetus production after embryo transfer. The gene-manipulated (tg; targeting of one or both alleles of gene encoding α-1,3-galactosyltransferase) or non-manipulated (control) bovine fetal fibroblasts were used for NT. The fibroblasts transfected with the targeting vector were selected with 0.4 mg mL−1 G418. The G418-resistant cells were monitored by PCR and Southern blot analysis. The cells (tg cells) in which homologous recombination occurred were used for NT. For NT, both tg cells and control cells were cultured in DMEM with 10% FCS. Early G1 cells were prepared by choosing pairs of bridged cells derived from mitotic phase cells (Urakawa M et al. 2004 Theriogenology 62, 714–728), and non-synchronized cells were obtained from a culture plate that had reached 60–80% confluence. Each donor cell was inserted into an enucleated, in vitro-matured (19 h) oocyte. Oocyte-cell couples were electrofused and activated with calcium ionophore and cycloheximide. The NT embryos were then co-cultured with bovine oviduct epithelial cells in CR1aa with 5% CS. The blastocyst rates were determined at 6 days after NT. The blastocysts were nonsurgically transferred to recipient heifers, and the developmental rate to the normal fetus was examined by the recovery of fetus or by using ultrasonography at Days 35–42. Data were analyzed by ANOVA. The developmental rate to the blastocyst stage did not differ significantly between tg (28.4%, 128/425) and control (25.4%, 181/739) cell groups. In the control group, the blastocyst rate of embryos constructed from early G1 phase fibroblasts (25.7%, 80/311) was not significantly different from that of embryos constructed with non-synchronized fibroblasts (23.6%, 101/428). In contrast, the blastocyst rate of tg cell derived-embryos was lower (P < 0.05) in early G1 phase (23.5%, 71/302) than in non-synchronized cell phase (46.3%, 57/123). The rate of development to a normal fetus in the tg group (15.4%, 4/26) was significant lower than that in the control group (62.5%, 25/40). For both the tg group and the control group, the rate of development to fetus tended to be higher (P > 0.05) for blastocysts derived from cells at the early G1 phase than for blastocysts derived from non-synchronized cells (tg group, 25.0%, 3/12 v. 7.1%, 1/14; control group, 90.0%, 9/10 v. 53.3%, 16/30). These results demonstrate that gene modification of fetal fibroblasts affects the development of NT embryos to fetuses. In addition, the synchronization of genetically modified donor cells to the early G1 phase may increase the potential to develop to a normal fetus.

Genomic organization and chromosomal mapping of the basic helix-loop-helix factor OUT (Tcf23/TCF23)

The genomic organization of Tcf23, the gene coding for mouse OUT, a basic helix-loop-helix transcription factor, was determined and its chromosome location was assigned to the A3 region of chromosome 5. By in silico searching, we further found the human counterpart of the mouse OUT gene (TCF23) in the draft human genome sequence and assigned it to 2p24-->p23.

Deficiency of phospholipase C-γ1 impairs renal development and hematopoiesis

Phospholipase C-γ1 (PLC-γ1) is involved in a variety of intracellular signaling via many growth factor receptors and T-cell receptor. To explore the role of PLC-γ1 in vivo, we generated the PLC-γ1-deficient (plc-γ1–/–) mice, which died of growth retardation at embryonic day 8.5-9.5 in utero. Therefore, we examined plc-γ1–/– chimeric mice generated with plc-γ1–/– embryonic stem (ES) cells for further study. Pathologically, plc-γ1–/– chimeras showed multicystic kidney due to severe renal dysplasia and renal tube dilation. Flow cytometric analysis and glucose phosphate isomerase assay revealed very few hematopoietic cells derived from the plc-γ1–/– ES cells in the mutant chimeras. However, differentiation of plc-γ1–/– ES cells into erythrocytes and monocytes/macrophages in vitro was observed to a lesser extent compared with control wild-type ES cells. These data suggest that PLC-γ1 plays an essential role in the renal development and hematopoiesis in vivo.

Limited effect of chromatin remodeling on D(beta)-to-J(beta) recombination in CD4+CD8+ thymocyte: implications for a new aspect in the regulation of TCR beta gene recombination

We have generated mutant mice in which TCR beta chain enhancer (E(beta)) was replaced with the TCR alpha chain enhancer (E(alpha)). Using this mouse model, we analyzed (i) recombination status of the TCR beta chain genes after functional V(D)J rearrangements occurred in the first allele during double-negative (DN)-to-double-positive (DP) transition and (ii) involvement of E(beta) for the expression of rearranged TCR beta chain genes. Our data show that E(alpha) substituted for E(beta) function to express a similar extent of TCR beta chains exactly at the same time as did E(beta) (CD25+CD44- DN stage), although the proportion of TCR beta+ cells at this stage was low in mutant mice. At the DP stage, germline transcription and histone acetylation of D(beta)-J(beta) loci were detectable at a high degree in both mutant and wild-type mice. However, DP cells in mutant mice retained the germline D(beta)-J(beta) configuration at a higher frequency than that of wild-type mice, whereas both DP cells expressed TCR beta chains to a similar extent. These data suggest that chromatin opening has a limited impact on D(beta)-to-J(beta) recombination at the DP stage and that E(alpha) is functionally equivalent to E(beta) in promoting expression of functionally rearranged TCR beta chain genes through DN-to-DP transition.

Production of cloned mice from embryonic stem cells arrested at metaphase

In mammals, cloned individuals can be produced from somatic cells. The combined use of gene targeting in embryonic stem cells and cloning contributes to the investigation of gene function in mammals. However, one of the major limitations to cloning is the low viability of cloned embryos, leading typically to high rates of pre- and postnatal death. The present study investigated whether cloning efficiency is influenced by the procedural differences involved in using transfected embryonic stem cells arrested at M phase for cloning by both single and serial transfer. In contrast to a previous study, in which fibroblasts were used, in the present study using embryonic stem cells there was no difference in the rate of production of cloned pups after the use of a single or serial nuclear transfer, although the proportion of blastocysts (70% versus 51%) was significantly higher (P < 0.001) after serial nuclear transfer. After embryo transfer of 445 blastocysts, 218 (49%) implanted and 27 (6% of blastocysts transferred) live pups were born. Of these 27 pups, 23 developed to adults of apparently normal fertility. Of these adults, 39% (n = 9) were derived from targeted embryonic stem cells, which is similar to the proportion of targeted embryonic stem cells in the population used for cloning. This study showed that cloning with embryonic stem cells is a viable procedure resulting in the production of transgenic cloned adults.

Set domain-containing protein, G9a, is a novel lysine-preferring mammalian histone methyltransferase with hyperactivity and specific selectivity to lysines 9 and 27 of histone H3

The covalent modification of histone tails has regulatory roles in various nuclear processes, such as control of transcription and mitotic chromosome condensation. Among the different groups of enzymes known to catalyze the covalent modification, the most recent additions are the histone methyltransferases (HMTases), whose functions are now being characterized. Here we show that a SET domain-containing protein, G9a, is a novel mammalian lysine-preferring HMTase. Like Suv39 h1, the first identified lysine-preferring mammalian HMTase, G9a transfers methyl groups to the lysine residues of histone H3, but with a 10-20-fold higher activity. It was reported that lysines 4, 9, and 27 in H3 are methylated in mammalian cells. G9a was able to add methyl groups to lysine 27 as well as 9 in H3, compared with Suv39 h1, which was only able to methylate lysine 9. Our data clearly demonstrated that G9a has an enzymatic nature distinct from Suv39 h1 and its homologue h2. Finally, fluorescent protein-labeled G9a was shown to be localized in the nucleus but not in the repressive chromatin domains of centromeric loci, in which Suv39 h1 family proteins were localized. This finding indicates that G9a may contribute to the organization of the higher order chromatin structure of non-centromeric loci.

Identification, cloning, and initial characterization of a novel mouse testicular germ cell-specific antigen

A monoclonal antibody, designated TES101, was raised by immunizing BALB/c mice with an allogenic mouse testicular homogenate followed by immunohistochemical selection as the initial screening method. By searching the expressed sequence tag (EST) database with the N-terminal amino acid sequence of TES101 reactive protein, we found that the predicted amino acid sequence encoded by a mouse testicular EST clone matched the TES101 protein sequence. Sequence analysis of the clone revealed no homologous molecule in the DNA/protein database. Based on data obtained from N-terminal amino acid analysis of the TES101 protein, the derived amino acid sequence contained a signal peptide region of 25 amino acids and a mature protein region of 225 amino acids, which translated into a protein with a molecular weight of 24 093. Northern blot analysis showed that mRNA of the TES101 protein was found in testis but not in any other mouse tissues examined. Western blot analysis revealed that TES101 reacted with a 38-kDa band on SDS-PAGE under nonreducing conditions, and this reactivity was abrogated under reducing conditions. Immunoelectron microscopic studies demonstrated that the molecule was predominantly located on the plasma membrane of spermatocytes and spermatids but not in Sertoli cells or interstitial cells, including Leydig cells. Thus, the TES101 protein is a novel molecule present primarily on the surface of developing male germ cells. TES101 protein may play a role in the processes underlying male germ cell formation.

A deletion of the paracellin-1 gene is responsible for renal tubular dysplasia in cattle

Various hereditary diseases analogous to particular human heritable diseases have been identified in cattle. Investigation of these cattle diseases will provide useful information regarding the pathogenesis of the corresponding human diseases. Renal tubular dysplasia is an autosomal recessive disease of Japanese black cattle characterized by renal failure and growth retardation. We have previously mapped the locus responsible for the disease within a region on bovine chromosome 1. In the present study, we further typed additional markers in this region and found that a genomic segment of bovine chromosome 1 including the microsatellite marker BMS4009 was deleted in the affected animals. Construction of a physical map covering this region with BAC clones and comparison of the nucleotide sequences of this region between normal and affected animals revealed that a region of 37 kb including exons 1 to 4 of the bovine paracellin-1 gene was deleted in the affected animals. The paracellin-1 gene, which is the causative gene for human renal hypomagnesemia with hypercaciuria and nephrocalcinosis, encodes a tight junction protein of renal epithelial cells. Therefore, we concluded that deletion of the paracellin-1 gene is responsible for renal tubular dysplasia of cattle, and the cattle disease could be a good model for the human disease.

Class switch recombination and hypermutation require activation-induced cytidine deaminase (AID), a potential RNA editing enzyme

Induced overexpression of AID in CH12F3-2 B lymphoma cells augmented class switching from IgM to IgA without cytokine stimulation. AID deficiency caused a complete defect in class switching and showed a hyper-IgM phenotype with enlarged germinal centers containing strongly activated B cells before or after immunization. AID-/- spleen cells stimulated in vitro with LPS and cytokines failed to undergo class switch recombination although they expressed germline transcripts. Immunization of AID-/- chimera with 4-hydroxy-3-nitrophenylacetyl (NP) chicken gamma-globulin induced neither accumulation of mutations in the NP-specific variable region gene nor class switching. These results suggest that AID may be involved in regulation or catalysis of the DNA modification step of both class switching and somatic hypermutation.

Telomere maintenance in telomerase-deficient mouse embryonic stem cells: characterization of an amplified telomeric DNA

Telomere dynamics, chromosomal instability, and cellular viability were studied in serial passages of mouse embryonic stem (ES) cells in which the telomerase RNA (mTER) gene was deleted. These cells lack detectable telomerase activity, and their growth rate was reduced after more than 300 divisions and almost zero after 450 cell divisions. After this growth crisis, survivor cells with a rapid growth rate did emerge. Such survivors were found to maintain functional telomeres in a telomerase-independent fashion. Although telomerase-independent telomere maintenance has been reported for some immortalized mammalian cells, its molecular mechanism has not been elucidated. Characterization of the telomeric structures in one of the survivor mTER(-/-) cell lines showed amplification of the same tandem arrays of telomeric and nontelomeric sequences at most of the chromosome ends. This evidence implicates cis/trans amplification as one mechanism for the telomerase-independent maintenance of telomeres in mammalian cells.

Appearance of sodium dodecyl sulfate-stable amyloid beta-protein (Abeta) dimer in the cortex during aging

We previously noted that some aged human cortical specimens containing very low or negligible levels of amyloid beta-protein (As) by enzyme immunoassay (EIA) provided prominent signals at 6 approximately 8 kd on the Western blot, probably representing sodium dodecyl sulfate (SDS)-stable Abeta dimer. Re-examination of the specificity of the EIA revealed that BAN50- and BNT77-based EIA, most commonly used for the quantitation of Abeta, capture SDS-dissociable Abeta but not SDS-stable Abeta dimer. Thus, all cortical specimens in which the levels of Abeta were below the detection limits of EIA were subjected to Western blot analysis. A fraction of such specimens contained SDS-stable dimer at 6 approximately 8 kd, but not SDS-dissociable A(beta) monomer at approximately 4 kd, as judged from the blot. This A(beta) dimer is unlikely to be generated after death, because (i) specimens with very short postmortem delay contained the A(beta) dimer, and (ii) until 12 hours postmortem, such SDS-stable A(beta) dimer is detected only faintly in PDAPP transgenic mice. The presence of A(beta) dimer in the cortex may characterize the accumulation of A(beta) in the human brain, which takes much longer than that in PDAPP transgenic mice.

A second p53-related protein, p73L, with high homology to p73

The p53 protein, which regulates the rate of cell division and death, is the most frequently mutated tumor suppressor to be identified so far in human cancers. Recently, a gene with significant homology to p53, termed p73, has been identified in a chromosomal region that is implicated in the molecular pathogenesis of neuroblastoma. We have cloned a second human p53-related gene, termed p73L, which shows strong amino-acid similarity to p73. The p73L gene is mapped to human chromosome 3q27-28 using in situ hybridization technique. p73L encodes a protein of 586 amino acids and its putative DNA binding domain (DBD) has high identities to those of p53 (60.6%) and to p73 (87.8%). Northern blot analysis, which demonstrated that the expression profiles of p73L and p73 mRNAs are distinct in some tissues, implies that p73 and p73L may have separate, distinct roles in different tissues.

Severe growth defect in mouse cells lacking the telomerase RNA component

The ribonucleoprotein enzyme telomerase synthesizes telomeric DNA onto chromosome ends. Telomere length is maintained, by the presence of telomerase activity, in the vast majority of primary tumours and stem cells, suggesting that telomere maintenance is essential for cellular immortalization. Recently, the telomerase RNA component in human and mouse (TERC and Terc, respectively), a telomerase-associated protein TEP1/TLP1 (refs 6,7) and the human catalytic subunit protein TERT (refs 8,9) have been identified. To examine the role of telomerase in telomere maintenance and cellular viability, we established Terc-deficient embryonic stem (ES) cells. It is known that telomerase activity is absent in cells from Terc-knockout mice. Although the study showed that telomere shortening was observed in the Terc-deficient cells from first to six generation animals, whether telomerase-dependent telomere maintenance was essential for cellular viability remained to be elucidated. To address this issue, we examined Terc-deficient ES cells under long-term culture conditions. Accompanying the continual telomere shortening, the growth rate of Terc-deficient ES cells was gradually reduced after more than 300 divisions. An impaired growth rate was maintained to approximately 450 divisions, and then cell growth virtually stopped. These data clearly show that telomerase-dependent telomere maintenance is critical for the growth of mammalian cells.

Regulation of Vbeta germline transcription in RAG-deficient mice by the CD3epsilon-mediated signals: implication of Vbeta transcriptional regulation in TCR beta allelic exclusion

During the thymic development of alphabeta lineage T cells, maturation of the CD4- CD8- double-negative (DN) cells into the CD4+ CD8+ double-positive cells is accompanied by the induction of TCR beta allelic exclusion. Recent studies have shown that these events are regulated by the signals through the pre-TCR complex which consists of the TCR beta, pre-TCR alpha and CD3 components. The Vbeta germline transcripts are detected prior to the TCR beta chain gene rearrangements in the DN thymocytes. To examine the effects of the pre-TCR-mediated signals on Vbeta germline transcription, we analyzed thymocytes from RAG-2-deficient mice treated with anti-CD3epsilon antibody. The germline transcripts of all Vbeta we examined, except for Vbeta14, were down-regulated by the anti-CD3epsilon antibody treatment. These data indicate that the regulation of Vbeta germline transcription by the signals through the pre-TCR complex may reflect the modulation of Vbeta accessibility to the VDJ recombinase, which contributes to TCR beta allelic exclusion.

Expression profile of the putative catalytic subunit of the telomerase gene

Telomerase, a ribonucleoprotein complex, adds hexameric repeats called telomeres to the growing ends of chromosomal DNA. The enzyme telomerase activity is present in a vast majority of tumors but is repressed in most normal tissues. Recently, two groups have reported the molecular cloning of the putative catalytic subunit (hEST2/hTRT) of the telomerase gene. We investigated the expression of this gene in diverse tumor-derived cell lines and tumors as well as in various normal tissues. The expression of hEST2/hTRT was detectable in tumor-derived cell lines, primary breast tumors, pancreatic tumors, and kidney tumors. Furthermore, the expression of hEST2/hTRT was down-regulated in response to a differentiation inducer. However, several normal tissues also expressed varying levels of hEST2/hTRT. Early passage cultures of endothelial fibroblasts and some epithelial cells also expressed the telomerase gene, albeit at low levels. In contrast, the expression of TLP1/TP1, the human homologue of Tetrahymena p80 telomerase subunit, was similar in all of these samples. Our results indicate that the differences in expression of hEST2/hTRT in tumor versus normal cells are relative and are not absolute.

Amyloid beta-protein deposition in the leptomeninges and cerebral cortex

To further investigate the process of amyloid beta-protein (Abeta) deposition, we determined, using sensitive enzyme immunoassays, the levels of Abeta40 and Abeta42 (Abetas) in the soluble and insoluble fractions of the leptomeninges (containing arachnoid mater and leptomeningeal vessels) and cerebral cortices from elderly control subjects showing various stages of Abeta deposition and from patients affected by Alzheimer's disease (AD). In both locations, insoluble Abeta levels were higher by orders of magnitude than soluble Abeta levels. Soluble Abeta levels in cortices were much lower than those in leptomeninges. In insoluble Abeta in the cortex, Abeta42 was by far the predominant species, and Abeta42 in AD cortices was characterized by the highest degree of modifications in the amino terminus. In contrast, this Abeta42 predominance was not observed in insoluble Abeta in the leptomeninges, which were found to be able to accumulate Abetas to an extent similar to that in the cortex, on a weight basis. The levels of insoluble Abeta in the leptomeninges or cortex generally correlated with the degree of cerebral amyloid angiopathy or the abundance of senile plaque, respectively. However, the presence of plaque-free cortical samples showing significant levels of insoluble Abeta42 suggests that biochemically detectable Abeta accumulation precedes immunocytochemically detectable Abeta deposition in the cortex.

Amyloid beta-protein (A beta) accumulation in the leptomeninges during aging and in Alzheimer disease

The results of well-characterized two-site enzyme immunoassays showed that the crude leptomeninges (consisting of the pia matter, arachnoid matter, and leptomeningeal vessels [LV]) from aged control brains and brains affected by Alzheimer disease (AD) contain very high levels of amyloid beta-protein (A beta). To learn about the source of A beta, we carefully dissected out both leptomeninges (LM) and LV under a dissecting microscope and determined the levels of soluble A beta in each. The purity of these dissected tissues was confirmed by the absence or presence of alpha-smooth muscle actin representing LV by Western blotting. Surprisingly, the amounts of A beta in each dissected sample were nearly equivalent on a weight basis. In each compartment from aged controls the level of A beta 1-42 was comparable to that of A beta 1-40, while in AD brain A beta 1-40 was a predominant species in both LM and LV. In some cases careful immunocytochemical examination revealed the presence of A beta deposits that were immunolabeled by several A beta monoclonal antibodies in leptomeningeal layers (most often in the arachnoid matter). The extent of A beta deposition in LM appeared to be much less than that explained by the soluble A beta levels, suggesting that immunocytochemically undetectable A beta can accumulate in LM. These observations indicate that leptomeninges are a large reservoir of A beta in normal aged individuals and in AD patients.

Commitment of immature CD4+8+ thymocytes to the CD4 lineage requires CD3 signaling but does not require expression of clonotypic T cell receptor (TCR) chains

As a consequence of positive selection in the thymus, immature CD4(+)8(+) double-positive, [DP] thymocytes selectively terminate synthesis of one coreceptor molecule and, as a result, differentiate into either CD4(+) or CD8(+) T cells. The decision by individual DP thymocytes to terminate synthesis of one or the other coreceptor molecule is referred to as lineage commitment. Previously, we reported that the intrathymic signals that induced commitment to the CD4 versus CD8 T cell lineages were markedly asymmetric. Notably, CD8 commitment appeared to require lineage-specific signals, whereas CD4 commitment appeared to occur in the absence of lineage-specific signals by default. Consequently, it was unclear whether CD4 commitment, as revealed by selective termination of CD8 coreceptor synthesis, occurred in all DP thymocytes, or whether CD4 commitment occurred only in T cell receptor (TCR)-CD3-signaled DP thymocytes. Here, we report that selective termination of CD8 coreceptor synthesis does not occur in DP thymocytes spontaneously. Rather, CD4 commitment in DP thymocytes requires signals transduced by either CD3 or zeta chains, which can signal CD4 commitment even in the absence of clonotypic TCR chains.

Activated Ras signals differentiation and expansion of CD4+8+ thymocytes

We describe a novel approach to assay the ability of particular gene products to signal transitions in lymphocyte differentiation in vivo. The method involves transfection of test expression constructs into RAG-1-deficient embryonic stem cells, which are subsequently assayed by the RAG-2-deficient blastocyst complementation approach. We have used this method to demonstrate that expression of activated Ras in CD4-8- (double negative, DN) prothymocytes in vivo induces their differentiation into small CD4+8+ (double positive, DP) cortical thymocytes with accompanying expansion to normal thymocyte numbers. However, activated Ras expression in DP cells does not cause proliferation or maturation to CD4+8- or CD4-8+ (single positive) thymocytes. Therefore, signaling through Ras is sufficient for promoting differentiation of DN to DP cells, but further differentiation requires the activity of additional signaling pathways.

Amyloid beta-proteins 1-40 and 1-42(43) in the soluble fraction of extra- and intracranial blood vessels

To investigate the process of amyloid beta-protein (A beta) accumulation in cerebral amyloid angiopathy (CAA), the levels of A beta were determined in the soluble fraction of extra- and intracranial blood vessels and leptomeninges obtained at autopsy. Two enzyme immunoassays were employed that are known to sensitively and specifically quantify two A beta species, A beta 1-40 and 1-42(43). A beta was detectable in the intracranial blood vessels and leptomeninges with the latter containing the highest levels, while it was undetectable in the extracranial blood vessels. Thus the levels of soluble A beta correlated well with the predilection sites for CAA. Among individuals aged 20 to 90, the A beta levels in the leptomeninges increased sharply in those aged 50 to 70 and thereafter tended to decline. However, only slight degrees of CAA were detected by immunocytochemistry, even when those leptomeninges contained high levels of A beta comparable with those in Alzheimer's disease. The level of A beta 1-42 was almost always severalfold that of A beta 1-40 in the soluble fraction of leptomeninges. This is in good agreement with the immunocytochemical result showing the presence of A beta 40-negative, A beta 42(43)-positive meningeal vessels. These results indicate that A beta 1-42 is the initially deposited species in CAA and that the disruption of A beta homeostasis precedes A beta deposition in the meningeal vessels.

CD3 epsilon and CD3 zeta cytoplasmic domains can independently generate signals for T cell development and function

To determine whether CD3 epsilon and CD3 zeta proteins have unique roles in TCR-dependent functions, chimeric genes encoding the extracellular and transmembrane domains of the human IL-2 receptor alpha chain (Tac) fused to a cytoplasmic domain of either the CD3 epsilon or CD3 zeta chain were introduced as transgenes into both normal and RAG2-deficient (RAG2-/-) mice. Developmental arrest of T lineage cells at the CD4, CD8 double-negative stage in the transgenic RAG2-/- thymus was released to the CD4, CD8 double-positive (DP) stage by in vivo cross-linking of TT epsilon or TT zeta with anti-Tac antibody. In TT epsilon + or TT zeta +, RAG2-/- mice, in vitro cross-linking of TT epsilon and TT zeta induced DP thymocyte cell death and proliferation of mature single-positive T cells. Overall, no qualitative differences were observed between TT epsilon- and TT zeta-mediated functions, suggesting that different CD3 components deliver qualitatively similar signals in inducing TCR-dependent functions.

Expression and induction of nuclear factor-kappa B-related proteins in thymocytes

Thymocytes mature in response to the cues from the thymic micro-environment, which regulate stage-specific gene expression during development. We find that several proteins that bind the kappa B sequence in vitro are constitutively activated in freshly isolated thymocytes. These include the rel-related p50 homodimers, p50/p65 heterodimers, low levels of c-rel, and two other factors that may be thymus specific. Disruption of the thymic micro-environment resulted in loss of DNA-binding, suggesting that lymphocyte-stromal cell interactions induce and maintain these proteins in a DNA-binding form. Phorbol ester and ionomycin treatment induced p50, p65, and p68 c-rel kappa B DNA-binding activity. Expression of p68 c-rel protein, but not p50 or p65, was suppressed by the immunosuppressive drug FK506. Because FK506 specifically inhibits the appearance of mature single-positive thymocytes, gene expression regulated by p68 c-rel may play a role in selection and maturational signals involved in the double-positive to single-positive transition.

Expression and induction of nuclear factor-kappa B-related proteins in thymocytes

Thymocytes mature in response to the cues from the thymic micro-environment, which regulate stage-specific gene expression during development. We find that several proteins that bind the kappa B sequence in vitro are constitutively activated in freshly isolated thymocytes. These include the rel-related p50 homodimers, p50/p65 heterodimers, low levels of c-rel, and two other factors that may be thymus specific. Disruption of the thymic micro-environment resulted in loss of DNA-binding, suggesting that lymphocyte-stromal cell interactions induce and maintain these proteins in a DNA-binding form. Phorbol ester and ionomycin treatment induced p50, p65, and p68 c-rel kappa B DNA-binding activity. Expression of p68 c-rel protein, but not p50 or p65, was suppressed by the immunosuppressive drug FK506. Because FK506 specifically inhibits the appearance of mature single-positive thymocytes, gene expression regulated by p68 c-rel may play a role in selection and maturational signals involved in the double-positive to single-positive transition.

Nuclear factors that mediate intrathymic signals are developmentally regulated

Thymocytes mature through several stages of development, defined by cell surface markers such as CD3, CD4, and CD8, in response to environmental cues. Signal transduction resulting from lymphocyte-stromal cell interactions is likely to activate inducible transcription factors which in turn govern stage-specific gene expression. In this report we show that inducible transcription factors such as AP-1 and NF-AT are constitutively nuclear, in response to intrathymic signals, in freshly isolated thymocytes at all stages of maturation. In CD4+CD8+ double positive (DP), but not in the more immature CD4-CD8- double negative (DN) thymocytes, constant stimulus from the thymic environment is required to maintain nuclear AP-1. Thus, disruption of the thymus and incubation of thymocytes at 37 degrees C downregulates DNA binding by nuclear factors AP-1 and NF-AT. Similar treatment of thymocytes has previously been shown to downregulate CD3 zeta chain phosphorylation and increase T cell receptor CD3 expression on DP thymocytes, which is a feature of repertoire selection. Since mature T cells maintain inducible nuclear factors in an inactive form until an encounter with antigen, we propose that downregulation of nuclear DNA binding proteins may reflect another feature of this stage of T cell maturation.

CD3 epsilon-mediated signals rescue the development of CD4+CD8+ thymocytes in RAG-2-/- mice in the absence of TCR beta chain expression

Recent studies have shown that TCR beta chain expression can effect the differentiation of CD4-CD8- double-negative (DN) thymocytes to CD4+CD8+ double-positive (DP) thymocytes. The TCR beta chain is expressed on the surface of DP thymocytes in association with CD3 gamma, delta and epsilon chains, suggesting a potential role for CD3 components in this signaling process. We now report detection of a very low level of surface expression of CD3 epsilon on adult DN RAG-2-/- thymocytes. This surface CD3 epsilon was associated with CD3 gamma and delta chains, as detected by anti-CD3 epsilon immunoprecipitation analyses. Significantly, injection of anti-CD3 epsilon mAb into RAG-2-/- mice led to the accumulation of an IL-2R alpha- CD2+ DP cell population and a nearly 100-fold increase in thymic cellularity to essentially normal levels. Together, these data strongly indicate that TCR beta chain-mediated developmental signals are transduced by CD3 components and provide potential insights into mechanisms by which TCR beta chain expression may effect this process.

Influence of immunoglobulin heavy- and light-chain expression on B-cell differentiation

To study the influence of immunoglobulin heavy-chain (HC) and light-chain (LC) expression in promoting B-cell differentiation, we have introduced functional immunoglobulin HC and/or LC transgenes into the recombinase activating gene-2-deficient background (RAG-2-/-). RAG-2-/- mice do not undergo endogenous V(D)J rearrangement events and, therefore, are blocked in B- and T-cell development at the early pro-B- and pro-T-cell stages. Introduction of immunoglobulin HC transgenes into the RAG-2-/- background promotes the development of a B-lineage cell population that phenotypically has the characteristics of pre-B cells. We have shown further that this population has altered growth characteristics as measured by interleukin-7 responsiveness in culture. Bone marrow cells from immunoglobulin HC transgenic RAG-2-/- mice have up-regulated expression of germ-line kappa LC gene transcripts and down-regulated expression of lambda 5 surrogate LCs (SLCs). Although mu HC/SLC complexes are detectable intracellularly in HC/RAG-2-/- pre-B-cell populations, HC expression is not readily detectable on the surface of these cells. lambda LC RAG-2-/- mice had a bone marrow B-lineage cell phenotype indistinguishable from that of RAG-2-/- littermates, indicating that LC expression by itself has no influence on pro-B cell differentiation. Strikingly, simultaneous introduction of mu HC and lambda LC transgenes into RAG-2-/- mice led to the generation of a substantial population of "monoclonal" peripheral B-cells that were functional with regard to immunoglobulin secretion, indicating that T cells or diverse immunoglobulin repertoires are not necessary for peripheral B-cell development.

The expression of Vpre-B/lambda 5 surrogate light chain in early bone marrow precursor B cells of normal and B cell-deficient mutant mice

Precursor B (pre-B) cells in bone marrow of normal and B cell-deficient mutant mice were analyzed for the expression of Vpre-B/lambda 5 surrogate light chain (SL). The surface expression of SL is confined to the early stages (pro-B and pre-B-I) of pre-B cell development and becomes undetectable once mu heavy chain (microH) is produced. The cell-cycle analysis revealed that cytoplasmic microH+ large cells (large pre-B-II), approximately 30% of which coexpressed SL in the cytoplasm, were most actively cycling, whereas cytoplasmic microH+ small cells (small pre-B-II) were SL- and not in cycle. The analysis of pre-B cells in B cell-deficient mice suggests that the large pre-B-II stage is a critical step for the selection and amplification of cells carrying functionally rearranged microH genes.

Probing immune functions in RAG-deficient mice

Inactivation of recombination activating gene (RAG)-1 or RAG-2 in mice results in the inability of developing lymphocytes to initiate V(D)J recombination, leading to the arrest of lymphocyte differentiation at a very early stage. Introduction of functionally assembled antigen-receptor genes or other potentially relevant genes into the RAG-deficient background can bypass the V(D)J recombination block and promote differentiation of the lymphocytes of RAG-deficient mice to various stages. This approach offers new means for analyzing the control of lymphocyte differentiation. In addition, generation of somatic chimeric mice by injecting mutant embryonic stem cells into the RAG-2-deficient blastocysts has also provided a powerful new method for assaying the potential roles of genes or regulatory elements in lymphocyte development or function.

Perforin-secreting killer cell infiltration and expression of a 65-kD heat-shock protein in aortic tissue of patients with Takayasu's arteritis

Cell-mediated autoimmunity has been strongly implicated in the pathogenesis of vascular cell injury in Takayasu's arteritis. To clarify the immunological mechanisms involved, we examined the expression of a cytolytic factor, perforin in infiltrating cells of aortic tissue samples from seven patients with Takayasu's arteritis. We also examined the expression of a 65-kD heat-shock protein (HSP-65), human leukocyte antigen classes I and II, and intercellular adhesion molecule-1 in the aortic tissue. Immunohistochemical studies showed that the infiltrating cells mainly consisted of gamma delta T lymphocytes, natural killer cells, macrophages, cytotoxic T lymphocytes and T helper cells, and that perforin was expressed in gamma delta T lymphocytes, natural killer cells, and cytotoxic T lymphocytes. In situ hybridization analysis also revealed expression of perforin mRNA in the infiltrating cells. Immunoelectron microscopic studies demonstrated that the infiltrating cells released massive amounts of perforin directly onto the surface of arterial vascular cells. We also found that expression of HSP-65, human leukocyte antigen classes I and II, and intercellular adhesion molecule-1 was strongly induced in the aortic tissue and might facilitate the recognition, adhesion and cytotoxicity of the infiltrating killer lymphocytes. These findings provide the first direct evidence that the infiltrating cells in the aortic tissue mainly consist of killer cells, and strongly suggest that these killer cells, especially gamma delta T lymphocytes, may recognize HSP-65 and play a critical role in the vascular cell injury of Takayasu's arteritis by releasing perforin.

Disappearance of the lymphoid system in Bcl-2 homozygous mutant chimeric mice

The bcl-2 proto-oncogene can prevent the death of many cell types. Mice were generated that were chimeric for the homozygous inactivation of bcl-2. Lymphocytes without Bcl-2 differentiated into phenotypically mature cells. However, in vitro, the mature T cells that lacked Bcl-2 had shorter life-spans and increased sensitivity to glucocorticoids and gamma-irradiation. In contrast, stimulation of CD3 inhibited the death of these cells. T and B cells with no Bcl-2 disappeared from the bone marrow, thymus, and periphery by 4 weeks of age. Thus, Bcl-2 was dispensable for lymphocyte maturation, but was required for a stable immune system after birth.

Evidence of perforin-mediated cardiac myocyte injury in acute murine myocarditis caused by Coxsackie virus B3

We have recently demonstrated that killer cells expressing a cytolytic factor, perforin, infiltrate the hearts of mice with acute viral myocarditis and may play an important role in the mechanism of myocardial damage. To clarify the mechanism of in vivo cardiac myocyte injury mediated by perforin, we investigated the release of perforin molecules from killer cells by immunoelectron microscopy and examined the circular lesions formed by perforin on the membrane of cardiac myocytes. We found that there was massive release of perforin molecules from the killer cells directly onto the surface of the cardiac myocytes. Furthermore, electron microscopy of ultrathin ventricular sections treated with trypsin revealed numerous circular lesions with the characteristics of perforin pores, in the membranes of cardiac myocytes. These findings provide the first direct evidence that killer cells injure cardiac myocytes by releasing perforin and may play a critical role in the myocardial damage occurring in acute viral myocarditis.

Fc gamma RII/III and CD2 expression mark distinct subpopulations of immature CD4-CD8- murine thymocytes: in vivo developmental kinetics and T cell receptor beta chain rearrangement status

We have recently identified a dominant wave of CD4-CD8- (double-negative [DN]) thymocytes in early murine fetal development that express low affinity Fc gamma receptors (Fc gamma RII/III) and contain precursors for Ti alpha/beta lineage T cells. Here we show that Fc gamma RII/III is expressed in very immature CD4low single-positive (SP) thymocytes and that Fc gamma RII/III expression is downregulated within the DN subpopulation and before the CD3-CD8low SP stage in T cell receptor (TCR)-alpha/beta lineage-committed thymocytes. DN Fc gamma RII/III+ thymocytes also contain a small fraction of TCR-gamma/delta lineage cells in addition to TCR-alpha/beta progenitors. Fetal day 15.5 DN TCR-alpha/beta lineage progenitors can be subdivided into three major subpopulations as characterized by cell surface expression of Fc gamma RII/III vs. CD2 (Fc gamma RII/III+CD2-, Fc gamma RII/III+CD2+, Fc gamma RII/III-CD2+). Phenotypic analysis during fetal development as well as adoptive transfer of isolated fetal thymocyte subpopulations derived from C57B1/6 (Ly5.1) mice into normal, nonirradiated Ly5.2 congenic recipient mice identifies one early differentiation sequence (Fc gamma RII/III+CD2(-)-->Fc gamma RII/III+CD2(+)-->Fc gamma RII/III-CD2+) that precedes the entry of DN thymocytes into the CD4+CD8+ double-positive (DP) TCRlow/- stage. Unseparated day 15.5 fetal thymocytes develop into DP thymocytes within 2.5 d and remain at the DP stage for > 48 h before being selected into either CD4+ or CD8+ SP thymocytes. In contrast, Fc gamma RII/III+CD2- DN thymocytes follow this same developmental pathway but are delayed by approximately 24 h before entering the DP compartment, while Fc gamma RII/III-CD2+ display accelerated development by approximately 24 h compared with total day 15.5 thymocytes. Fc gamma RII/III-CD2+ are also more developmentally advanced than Fc gamma RII/III+CD2- fetal thymocytes with respect to their TCR beta chain V(D)J rearrangement. At day 15.5 in gestation, beta chain V(D)J rearrangement is mostly, if not entirely, restricted to the Fc gamma RII/III-CD2+ subset of DN fetal thymocytes. Consistent with this analysis in fetal thymocytes, > 90% of adult thymocytes derived from mice carrying a disrupting mutation at the recombination-activating gene 2 locus (RAG-2-/-) on both alleles are developmentally arrested at the DN CD2- stage. In addition, there is a fivefold increase in the relative percentage of thymocytes expressing Fc gamma RII/III in TCR and immunoglobulin gene rearrangement-incompetent homozygous RAG-2-/- mice (15% Fc gamma RII/III+) versus rearrangement-competent heterozygous RAG-2+/- mice (< 3% Fc gamma RII/III+). Thus, Fc gamma RII/III expression defines an early DN stage preceding V beta(D beta)I beta rearrangement, which in turn is followed by surface expression of CD2. Loss of Fc gamma RII/III and acquisition of CD2 expression characterize a late DN stage immediately before the conversion into DP thymocytes.

Restoration of T cell development in RAG-2-deficient mice by functional TCR transgenes

Introduction of TCR alpha transgene, TCR beta transgene, or both into RAG-2-/-mice differentially rescues T cell development. RAG-2-/- mice have small numbers of TCR-CD4-CD8-(double negative, DN) thymocytes that express CD3 gamma delta epsilon and zeta proteins intracellularly. Introduction of a TCR beta transgene, but not a TCR alpha transgene, into the RAG-2-/- background restored normal numbers of thymocytes. These cells were CD4+CD8+ (double positive, DP) and expressed small amounts of surface TCR beta chain dimers in association with CD3 gamma delta epsilon but not zeta. RAG-2-/- mice that expressed alpha and beta TCR transgenes developed both DP and single positive thymocytes. Thus, the TCR beta subunit, possibly in association with a novel CD3 complex, participates in the DN to the DP transition.

Expression of perforin and cytolytic potential of human peripheral blood lymphocyte subpopulations

To verify the physiological role of the pore-forming protein perforin in vivo, its expression in subpopulations of human peripheral blood lymphocytes was examined by immunocytochemical staining and their cytolytic potentials compared. In addition to NK cells and gamma delta T cells, which uniformly expressed abundant perforin in their cytoplasmic granules, only a small subpopulation of CD8+ alpha beta T cells contained perforin, namely the CD11b+ subset. However, in vitro activation with an anti-CD3 antibody and IL-2 induced perforin expression in approximately 50% of the CD8+CD11b- T cells and also in a small subset of CD4+ T cells. A distribution of perforin in CD8+ and CD4+ T cells, similar to in vitro activated T cells, was observed in fresh peripheral blood lymphocytes from infectious mononucleosis patients. In all instances, the expression of perforin correlated with the cytolytic potential of these subpopulations. The results strongly suggest that perforin plays a role in the manifestation of cytotoxic activity in vivo.

Cellular and molecular bases for the immunopathology of the myocardial cell damage involved in acute viral myocarditis with special reference to dilated cardiomyopathy

Cell-mediated autoimmunity has been strongly implicated in the pathogenesis of the myocardial cell damage involved in viral myocarditis. To investigate the cellular and molecular bases of both target cells and effector cells for cell-mediated cytotoxicity involved in viral myocarditis and dilated cardiomyopathy, we first examined the expression of major histocompatibility complex (MHC) antigens and a cell adhesion molecule, intercellular adhesion molecule-1 (ICAM-1) in myocardial cells of a murine model of viral myocarditis and in patients with acute myocarditis and dilated cardiomyopathy. Secondly, we analyzed the characteristics of the infiltrating cells in the heart, especially the expression of a cytolytic factor, perforin. We found that Coxsackievirus B3 (CVB3)-induced murine acute myocarditis resulted in enhanced expression of MHC (class I) antigens and ICAM-1 on myocardial cells, and that perforin was abundantly expressed in NK (natural killer)-like large granular lymphocytes (LGL), which represent the main infiltrating cell type in the early stage. Immunoelectron microscopic study showed killer cells directly damaging cardiac myocytes by the release of perforin. Perforin was also expressed in the infiltrating cells in the heart of a patient with acute myocarditis. Both MHC antigens and ICAM-1 were clearly expressed in the hearts of patients with acute myocarditis and dilated cardiomyopathy. These data provided direct evidence that cell-mediated cytotoxicity plays a critical role in the myocardial cell damage involved in viral myocarditis.

Function and control of recombination-activating gene activity

The RAG-1 and RAG-2 genes synergistically confer VDJ recombinase activity to nonlymphoid cell lines. To unequivocally test RAG gene function, we created lines of mice that lack functional copies of these genes. Consistent with the possibility that RAG gene encode the tissue-specific components of VDJ recombinase, RAG-2-deficient mice are viable but have a severe combined immune deficiency due to inability to initiate VDJ recombination and thereby generate mature lymphocytes. RAG-2-deficient mice have no obvious defect in any tissue or lineage other than lymphocytes, indicating that VDJ recombinase activity and RAG-2-gene function is required only for lymphocyte development. Levels of RAG-1 and RAG-2 expression in primary murine lymphoid tissues and lymphoid bone marrow cultures generally are much higher than those of transformed precursor B-cell lines. Low-level RAG gene expression in permanent cell lines results from a decline during propagation due to outgrowth of cells with lower RAG expression levels. The low and variable level of RAG gene expression in transformed pre-B cell lines correlates with low and variable rates of endogenous VDJ recombination; therefore, such lines are not reliable models for experiments aimed at studying mechanisms that target this activity to particular variable region gene segments. To generate such a system, we introduced RAG genes into B-lineage lines under the control of a heat shock-inducible promoter; heat-shock treatment induces extremely high-level but transient RAG expression accompanied by parallel induction of VDJ recombinase activity. Such cells efficiently rearrange transfected VDJ recombination substrates in a regulated manner that is dependent on the activity of transcriptional control elements associated with the target V gene segments.

Expression of perforin in murine natural killer cells and cytotoxic T lymphocytes in vivo

We have previously detected perforin expression in a subpopulation of asialo GM1+ natural killer (NK) cells and CD8+ T lymphocytes in murine spleen cells by immunocytochemical staining with an anti-perforin monoclonal antibody. In the present study, more detailed analyses of perforin expression in murine cytotoxic lymphocyte subpopulations were performed. The expression of perforin in asialo GM1+ spleen cells was predominantly confined to the NK1.1+ subset, where all NK activity also resided. Perforin expression was also studied on alloreactive cytotoxic T lymphocyte (CTL) induced in vivo. The cells expressing perforin in peritoneal exudate lymphocytes predominantly resided in the CD8+ T cell subpopulation co-expressing asialo GM1 where an allospecific CTL activity also resided. Furthermore, the percentage of perforin-positive cells in this population was greatly reduced after stimulation with anti-CD3 or anti-T cell receptors antibodies, which induce serine esterase release from the cytoplasmic granules. These findings highly suggest that perforin is involved in in vivo NK cell- and CTL-mediated cytolysis.

RAG-2-deficient mice lack mature lymphocytes owing to inability to initiate V(D)J rearrangement

We have generated mice that carry a germline mutation in which a large portion of the RAG-2 coding region is deleted. Homozygous mutants are viable but fail to produce mature B or T lymphocytes. Very immature lymphoid cells were present in primary lymphoid organs of mutant animals as defined by surface marker analyses and Abelson murine leukemia virus (A-MuLV) transformation assays. However, these cells did not rearrange their immunoglobulin or T cell receptor loci. Lack of V(D)J recombination activity in mutant pre-B cell lines could be restored by introduction of a functional RAG-2 expression vector. Therefore, loss of RAG-2 function in vivo results in total inability to initiate V(D)J rearrangement, leading to a novel severe combined immune deficient (SCID) phenotype. Because the SCID phenotype was the only obvious abnormality detected in RAG-2 mutant mice, RAG-2 function and V(D)J recombinase activity, per se, are not required for development of cells other than lymphocytes.

Perforin is expressed in CTL populations generated in vivo

Immunization of C57BL/6 mice with syngeneic tumor cells, MBL-2, resulted in the generation of antitumor effector cells in vivo. The immunized C57BL/6 mice permanently rejected viable MBL-2 lymphoma cells, but not B16 melanoma cells. Cytotoxic T cells obtained from MBL-2-immunized mouse peritoneal cells (PEC) showed specific cytotoxicity against MBL-2, but not to YAC-1, RDM-4 and Meth A cells. By sorting with FACStar, the specific CTL were characterized as TCR alpha beta+ CD8+ T cells. Moreover, the cytoplasm of in vivo-induced CTL was stained with a monoclonal antibody against perforin. The localization of perforin in cytoplasmic granules of CTL was demonstrated by electron microscope analysis. This experiment presented the first evidence that in vivo-induced CD8+ CTL against syngeneic tumor cells expressed significant amounts of perforin.