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Mice with null mutations of ciliary neurotrophic factor (Cntf) receptor alpha (Cntf-Ralpha), or cytokine-like factor 1 (Clf), one component of Cntf-II (a heterodimeric Cntf-Ralpha ligand), die as neonates from motor neuron loss affecting the facial nucleus and ventral horn of the lumbar spinal cord. Exposure to cardiotrophin-like cytokine (Clc), the other putative Cntf-II element, supports motor neuron survival in vitro and in ovo. Confirmation that Clc ablation induces an equivalent phenotype to Clf deletion would support a role for Clc in the functional Cntf-II complex. In this study, Clc knockout mice had decreased facial motility, did not suckle, died within 24 hours, and had 32% and 29% fewer motor neurons in the facial nucleus and lumbar ventral horn, respectively; thus, Clc is essential for motor neuron survival during development. The concordance of the Clc knockout phenotype with those of mice lacking Cntf-Ralpha or Clf bolsters the hypothesis that Clc participates in Cntf-II.

IP-10 secretion is induced by pro-inflammatory cytokines and mediates the migration of CXCR3+ cells. Its elevation in clinical samples has been associated with multiple inflammatory diseases and its antagonism has been reported to be effective in several animal models of inflammatory disease. We generated a mouse anti-mouse IP-10 monoclonal antibody (mAb; Clone 20A9) that specifically bound murine IP-10 with high affinity and inhibited in vitro IP-10 induced BaF3/mCXCR3 cell migration with an IC(50) of approximately 4 nM. The 20A9 mAb was completely absorbed in vivo and had dose proportional pharmacokinetic exposure with a serum half life of 2.4-6 days. The 20A9 mAb inhibited IP-10 mediated T-cell recruitment to the airways, indicating that it is effective in vivo. However, administration of the 20A9 mAb had no significant effect on disease in mouse models of delayed type hypersensitivity, collagen induced arthritis, cardiac allograft transplantation tolerance, EAE or CD4+ CD45RBHi T-cell transfer-induced IBD. These data suggest that the 20A9 mAb can antagonize IP-10 mediated chemotaxis in vitro and in vivo and that this is insufficient to cause a therapeutic benefit in multiple mouse models of inflammatory disease.

Background: Current immunosuppression regimens are toxic to transplant recipients and, in many cases, acute rejection episodes occur because of escape of donor-reactive lymphocytes from the immunosuppression. T cells are the mediators of acute, cell-mediated graft damage and are hypothesized to use the CXCR3 chemokine axis for migration into the allograft. This study investigates the effect of CXCR3 blockade using a nonpeptide, small molecule inhibitor, AMG1237845, in murine cardiac allograft survival., Methods: C57BL/6 (H-2) mice received vascularized cardiac allografts from A/J (H-2) donors and were treated with the CXCR3 antagonist. Histologic and flow cytometric analyses were used to measure infiltration of leukocytes, and quantitative reverse-transcriptase polymerase chain reaction and interferon-gamma ELISPOT assays were used to measure donor-specific reactivity., Results: CXCR3 antagonism modestly prolonged allograft survival compared with vehicle treatment, but at time-matched intervals posttransplant, neutrophil, CD8, and CD4 T cell infiltration was indistinguishable. Although proliferation of donor-reactive naïve T cells was unaffected by CXCR3 antagonism, the frequency of interferon-gamma-producing cells in the recipient spleen was significantly reduced by AMG1237845 treatment. CXCR3 blockade for 30 days synergized with short-term, low-dose anti-CD154 monoclonal antibodies to prolong survival past 50 days in 75% of grafts and past 80 days in 25% of the cases., Conclusions: These results indicate that in synergy with co-stimulation blockade, CXCR3 is a viable therapeutic target to prevent acute graft rejection.

Autoimmune diseases are marked by the presence of class-switched, high-affinity autoantibodies with pathogenic potential. Costimulation plays an important role in the activation of T cells and the development of T cell-dependent B cell responses. ICOS plays an indispensable role in the development of follicular helper T cells (T(FH) cells), which provide cognate help to germinal center (GC) B cells. We show that the levels of T(FH) cells and GC B cells in two different models of autoimmunity, the New Zealand Black/New Zealand White (NZB/NZW) F(1) mouse model of systemic lupus erythematosus and the collagen-induced arthritis model of rheumatoid arthritis, are dependent on the maintenance of the ICOS/B7RP-1 pathway. Treatment with an anti-B7RP-1 Ab ameliorates disease manifestations and leads to a decrease in T(FH) cells and GC B cells as well as an overall decrease in the frequency of ICOS(+) T cells. Coculture experiments of Ag-primed B cells with CXCR5(+) or CXCR5(-) T cells show that blocking B7RP-1 does not directly impact the production of IgG by B cells. These findings further support the role of ICOS in autoimmunity and suggest that the expansion of the T(FH) cell pool is an important mechanism by which ICOS regulates Ab production.

Formative research assessing human papillomavirus (HPV) vaccine readiness in Uganda was conducted in 2007. The objective was to generate evidence for government decision-making and operational planning for HPV vaccine introduction. Qualitative research methods with children, parents, teachers, community leaders, health workers, technical experts and political leaders were used to capture understanding of socio-cultural, health system and policy environments. We found low levels of knowledge about cervical cancer and HPV. Vaccination and its benefits were well-understood; respondents were positive about HPV vaccination. Health systems were deemed adequate for HPV vaccine delivery. Schools were identified as a vaccination venue, given high attendance by girls aged 10-12 years. Communication and advocacy strategies to foster acceptance should provide information on cervical cancer, HPV vaccine safety, and side effects. Policymakers requested further detail on costs. Introduction of HPV vaccine could be integrated into existing reproductive health and immunization policies.

Deposition of beta-amyloid (Abeta) peptides in the walls of brain blood vessels, cerebral amyloid angiopathy (CAA), is common in patients with Alzheimer's disease (AD). Previous studies have demonstrated Abeta peptide deposition among vascular smooth muscle cells (VSMCs), but the source of the Abeta and basis for its selective deposition in VSMCs are unknown. In the present study, we examined the deposition patterns of Abeta peptides, Abeta40 and Abeta42, within the cerebrovasculature of AD and control patients using single- and double-label immunohistochemistry. Abeta40 and Abeta42 were abundant in VSMCs, especially in leptomeningeal arteries and their initial cortical branches; in later-stage AD brains this pattern extended into the microvasculature. Abeta peptide deposition was linked to loss of VSMC viability. Perivascular leak clouds of Abeta-positive material were associated primarily with arterioles. By contrast, control brains possessed far fewer Abeta42- and Abeta40-immunopositive blood vessels, with perivascular leak clouds of Abeta-immunopositive material rarely observed. We also demonstrate that VSMCs in brain blood vessels express the alpha7 nicotinic acetylcholine receptor (alpha7nAChR), which has high binding affinity for Abeta peptides, especially Abeta42. These results suggest that the blood and blood-brain barrier permeability provide a major source of the Abeta peptides that gradually deposit in brain VSMCs, and the presence and abundance of the alpha7nAChR on VSMCs may facilitate the selective accumulation of Abeta peptides in these cells.

We conducted a prospective, descriptive study in the Clinica Anglo Americana, a prívate institution taking care of patients from a medium-high socioeconomic level in Lima. The goal of the study was to determine the frequency of histologic findings in liver biopsies performed by laparoscopy or percutaneously in patients with overweight (body mass index > 25 kg/m2) or obesity (body mass index > 30 kg/m2), and to evaluate the correlation with antropometric variables such as BMI, waist circumference, history of diabetes or hyperlypidemia, and biochemical variables like glycemia, lipid profile, aminotransferases and AST/ALT ratio. Between the years 2001 and 2006 50 patients were biopsied, 29 with overweight and 21 with obesity. Eighteen had simple steatosis and 22 had Non-alcoholic steatohepatitis (NASH) (44%), so 40 patients (80%) had some form of fatty liver. Five patients (10%) had cirrhosis confirmed by biopsy, and in all of them the finding of cirrhosis was completely incidental. Sixty four percent of patients with NASH were obese, like the 5 cirrhotics in our series. Herein we illustrate that in a relatively small sample of patients with obesity and overweight like ours, we found all the forms of the liver steatosis spectrum, from simple steatosis to cirrhosis, with a high frequency of NASH.

We have investigated the possibility that soluble, blood-borne amyloid beta (Abeta) peptides can cross a defective blood-brain barrier (BBB) and interact with neurons in the brain. Immunohistochemical analyses revealed extravasated plasma components, including Abeta42 in 19 of 21 AD brains, but in only 3 of 13 age-matched control brains, suggesting that a defective BBB is common in AD. To more directly test whether blood-borne Abeta peptides can cross a defective BBB, we tracked the fate of fluorescein isothiocyanate (FITC)-labeled Abeta42 and Abeta40 introduced via tail vein injection into mice with a BBB rendered permeable by treatment with pertussis toxin. Both Abeta40 and Abeta42 readily crossed the permeabilized BBB and bound selectively to certain neuronal subtypes, but not glial cells. By 48 h post-injection, Abeta42-positive neurons were widespread in the brain. In the cerebral cortex, small fluorescent, Abeta42-positive granules were found in the perinuclear cytoplasm of pyramidal neurons, suggesting that these cells can internalize exogenous Abeta42. An intact BBB (saline-injected controls) blocked entry of blood-borne Abeta peptides into the brain. The neuronal subtype selectivity of Abeta42 and Abeta40 was most evident in mouse brains subjected to direct intracranial stereotaxic injection into the hippocampal region, thereby bypassing the BBB. Abeta40 was found to preferentially bind to a distinct subset of neurons positioned at the inner face of the dentate gyrus, whereas Abeta42 bound selectively to the population of large neurons in the hilus region of the dentate gyrus. Our results suggest that the blood may serve as a major, chronic source of soluble, exogenous Abeta peptides that can bind selectively to certain subtypes of neurons and accumulate within these cells.

Butyrophilin-like 2 (BTNL2) is a butyrophilin family member with homology to the B7 costimulatory molecules, polymorphisms of which have been recently associated through genetic analyses to sporadic inclusion body myositis and sarcoidosis. We have characterized the full structure, expression, and function of BTNL2. Structural analysis of BTNL2 shows a molecule with an extracellular region containing two sets of two Ig domains, a transmembrane region, and a previously unreported cytoplasmic tail. Unlike most other butyrophilin members, BTNL2 lacks the prototypical B30.2 ring domain. TaqMan and Northern blot analysis indicate BTNL2 is predominantly expressed in digestive tract tissues, in particular small intestine and Peyer's patches. Immunohistochemistry with BTNL2-specific Abs further localizes BTNL2 to epithelial and dendritic cells within these tissues. Despite its homology to the B7 family, BTNL2 does not bind any of the known B7 family receptors such as CD28, CTLA-4, PD-1, ICOS, or B and T lymphocyte attenuator. Because of its localization in the gut and potential role in the immune system, BTNL2 expression was analyzed in a mouse model of inflammatory bowel disease. BTNL2 is overexpressed during both the asymptomatic and symptomatic phase of the Mdr1a knockout model of spontaneous colitis. In functional assays, soluble BTNL2-Fc protein inhibits the proliferation of murine CD4(+) T cells from the spleen, mesenteric lymph node, and Peyer's patch. In addition, BTNL2-Fc reduces proliferation and cytokine production from T cells activated by anti-CD3 and B7-related protein 1. These data suggest a role for BTNL2 as a negative costimulatory molecule with implications for inflammatory disease.

A uniquely structured SiO(x)-capped (x = 0.5-0.8) Si nanowire array with strong blue emission, like a nanobeacon array, was fabricated using electroless metal (silver) deposition on a water plasma-treated Si wafer. Formation of the nanoscale light source array can be understood on the basis of a self-assembled localized microscopic electrochemical cell model and a diffusion-limited aggregation process. Photoluminescence spectral analysis reveals that the intensity of the broad blue-emitting luminescent band centred at around 435 nm strongly depends upon the irradiation of H(2)O(+), HO(+), and O(+) ions, which are present in the water plasma. We attribute the blue PL band to the optical transition of the self-trapped excitons at the surfaces of SiO(x) nanocaps.

Using electrochemical etching of a polycrystalline 3C-SiC target and subsequent ultrasonic treatment in water solution, we have fabricated suspensions of 3C-SiC nanocrystallites that luminesce. Transmission electron microscope observations show that the 3C-SiC nanocrystallites, which uniformly disperse in water, have sizes in the range of 1-6 nm. Photoluminescence and photoluminescence excitation spectral examinations show clear evidence for the quantum confinement of 3C-SiC nanocrystallites with the emission band maximum ranging from 440 to 560 nm. Tunable, composite polystyrene/SiC film can be made by adding polystyrene to a toluene suspension of the 3C-SiC nanocrystallites and then coating the resulting solution onto a Si wafer.

Four groups of Si nanostructures with and without beta-SiC nanocrystals were fabricated for clarifying the origin of a blue emission with a double-peak structure at 417 and 436 nm. Spectral analyses and microstructural observations show that the blue emission is related to the existence of excess Si atoms in these Si nanostructures. The energy levels of electrons in Si nanocrystals with vacancy defects formed from the excess Si atoms are calculated and the characteristics of the obtained density of states coincide with the observed double-peak emission. The present work provides a possible mechanism of the blue emission in various Si nanostructures.

CD4 gene regulation provides an ideal model for understanding the molecular events that drive T cell development. In this paper we use a transgenic approach to identify a CD4 LCR containing a stage-specific thymocyte enhancer (TE) and a region that protects against position effect variegation. Surprisingly, the TE acts indirectly through the previously defined proximal enhancer and is strongly induced upon commitment to the T cell lineage. We also describe a complex series of hierarchical control element interactions that orchestrate CD4 expression throughout thymopoiesis. These data provide a framework for understanding how CD4 gene expression is regulated in response to lineage commitment decisions.

T cell lineage commitment as the double-positive (DP) thymocyte matures into the single-positive (SP) T cell requires the irreversible repression or maintenance of CD4 gene expression. Signals transmitted from the T cell antigen receptor (TCR) during thymic selection are believed to be linked to the transcriptional regulation of the CD4 gene; thus, a study of the factors that control CD4 gene expression may lead to further insight into the molecular mechanisms that drive T cell development. This review discusses the work conducted to date to identify and characterize the transcriptional control elements in the CD4 locus and the factors that mediate their function. From these studies, it is clear that the molecular mechanisms controlling CD4 gene expression are very complex and are controlled by many different signals as the thymocyte develops.

The control of CD4 gene expression is essential for proper T lymphocyte development. Signals transmitted from the T-cell antigen receptor (TCR) during the selection process are believed to be linked to the regulation of CD4 gene expression during specific stages of T cell development. Thus, the control CD4 gene expression is an ideal model system for studying the molecular mechanisms that drive T cell development. Here, I discuss the characterization of transcriptional control elements in the CD4 locus and the factors that mediate their function. The study of these elements has led to significant insights into the mechanisms in which the T lymphocyte develops it mature functional characteristics.

Expression of the CD4 gene is tightly controlled throughout thymopoiesis. The downregulation of CD4 gene expression in CD4(-) CD8(-) and CD4(-) CD8(+) T lymphocytes is controlled by a transcriptional silencer located in the first intron of the CD4 locus. Here, we determine that the c-Myb transcription factor binds to a functional site in the CD4 silencer. As c-Myb is also required for CD4 promoter function, these data indicate that depending on the context, c-Myb plays both positive and negative roles in the control of CD4 gene expression. Interestingly, a second CD4 silencer-binding factor, HES-1, binds to c-Myb in vivo and induces it to become a transcriptional repressor. We propose that the recruitment of HES-1 and c-Myb to the silencer leads to the formation of a multifactor complex that induces silencer function and repression of CD4 gene expression.

Si-based Er-doped Si nanostructures were fabricated for exploring efficient light emission from Er ions and Si nanocrystallites. High-resolution transmission electron microscopy observations reveal that Si nanocrystallites are spherically embedded in the SiO2 matrix. Energy-dispersive x-ray analysis indicates that the Er centers are distributed at the surfaces of nanocrystallites surrounded by the SiO2 matrix. Low-frequency Raman scattering investigation shows that Lamb's theory can be adopted to exactly calculate the surface vibration frequencies from acoustic phonons confined in spherical Si nanocrystallites and the matrix effects are negligible.

The control of CD4 expression is essential for proper T lymphocyte development. We have previously described a cis-acting silencer element required for repressing transcription of the CD4 gene. Here we report the cloning and characterization of a novel factor that binds to a critical functional site in the CD4 silencer. This factor, referred to as silencer-associated factor (SAF), is a member of the helix-turn-helix factor family and shares sequence similarity with the homeodomain class of transcriptional regulators. Introduction of a specific mutation into the SAF binding site in the CD4 silencer abrogates silencer activity in transgenic mice, supporting the hypothesis that SAF is important in mediating silencer function. Although SAF is expressed in all lymphocytes, immunofluorescence studies indicate that SAF is present primarily in the cytoplasm in T cells in which the endogenous silencer is nonfunctional, whereas it is present primarily in the nucleus in T cells in which the silencer is functional. We thus hypothesize that the subclass-specific subcellular compartmentalization of SAF plays an important role in mediating the specificity of function of the CD4 silencer during T cell development.

The control of CD4 gene expression is essential for proper T lymphocyte development. Signals transmitted from the T-cell antigen receptor (TCR) during the thymic selection processes are believed to be linked to the regulation of CD4 gene expression during specific stages of T cell development. Thus, a study of the factors that control CD4 gene expression may lead to further insight into the molecular mechanisms that drive thymic selection. In this review, we discuss the work conducted to date to identify and characterize the cis-acting transcriptional control elements in the CD4 locus and the DNA-binding factors that mediate their function. From these studies, it is becoming clear that the molecular mechanisms controlling CD4 gene expression are very complex and differ at each stage of development. Thus, the control of CD4 expression is subject to many different influences as the thymocyte develops.

The c-Myb transcription factor is important for fetal hematopoiesis and has been proposed to mediate later stages of lymphocyte development. Using homozygous null c-Myb/Rag1 chimeric mice, we have determined that c-Myb plays an important role in the differentiation of macrophages and lymphocytes from precursor stem cells. We also determine that deletion of c-Myb leads to a complete block in early T cell development just before the oligopotent thymocyte matures into the definitive T cell precursor. These data indicate that c-Myb plays an important role at multiple stages of hematopoiesis and is required at an early stage of T cell development.

We have previously identified a transcriptional silencer that is critical for proper expression of the CD4 gene during T-cell development. Here we report that the Hairy/Enhancer of Split homologue HES-1, a transcription factor in the lin12/Notch signaling pathway, binds to an important functional site in the CD4 silencer. Overexpression of HES-1 leads to the silencer site-dependent repression of CD4 promoter and enhancer function as well as the downregulation of endogenous CD4 expression in CD4(+) CD8(-) TH cells. Interestingly, overexpression of an activated form of Notch1 (NotchIC) leads to the repression of CD4 promoter and enhancer function both in the presence and absence of the silencer. NotchIC-mediated CD4 silencer function is not affected by the deletion of the HES-1-binding site, indicating that multiple factors binding to CD4 transcriptional control elements are responsive to signaling from this pathway, including other silencer-binding factors. Taken together, these data are consistent with the hypothesis that the lin12/Notch signaling pathway is important in thymic development and provide a molecular mechanism via the control of CD4 gene expression in which the lin12/Notch pathway affects T-cell developmental fate.

NF-IL6 is an important transcriptional regulator of genes induced in activated monocytes/macrophages, and NF-IL6 is the only CCAAT/enhancer-binding protein (C/EBP) family member whose steady-state mRNA levels increase upon activation of monocytes (1). We show that increased transcription of the NF-IL6 gene is responsible, at least in part, for induction of NF-IL6 mRNA following activation of U937 promonocytic cells. We have identified a 104-bp minimal promoter region of the NF-IL6 gene that is sufficient for basal and activation-dependent induction of transcription in U937 cells. This region contains binding sites for the cAMP response element-binding protein/activation transcription factor (CREB/ATF) and Sp1 families of transcription factors. Each site is functionally important and contributes independently to transcription of the NF-IL6 gene in U937 cells.

We propose two designs with which one can obtain a circular light disk with both uniform irradiance and phase, namely, a homodisk on a plane target from a TEM(0, 0) Gaussian beam. The first design is pure-phase filtering masks based on wave theory and computer simulation. The second design, an aspherical lens, satisfies the two requirements successively. We used geometrical optics to obtain uniform irradiance with the aspherical lens. The theoretical results of both designs are reasonably good.

We and others have defined a transcriptional silencer critical for the proper expression of the CD4 gene at all stages of T cell development. In this report, we use biochemical techniques to identify three different factor-binding sites within the CD4 silencer, denoted sites I, II, and III. Using transgenic analyses, we determine that although all three factor-binding sites are important for silencer activity, there is significant redundancy in that the presence of either site II alone, or the combination of sites I and III permits silencer function. Thus, our data indicate that the mechanism of function of the CD4 silencer is extremely complex. Further biochemical analyses indicate that the factor binding to site II has the same sequence specificity as a factor binding to an E box site in the CD4 enhancer; thus, a member of the bHLH factor family may be important in mediating silencer function.

T lymphocytes play an important role in the generation, maintenance, and specificity of the skin immune response. T cells are the predominant class of lymphocytes found in the skin and moderate many of the initial immune responses, such as allergic contact and delayed-type hypersensitivity. In addition, the primary class of cutaneous lymphomas is believed to be of T-cell lineage. All of the antigen and MHC-restriction capabilities are manifested by the T-cell antigen receptor (TCR), the study of which has been the primary focus of immunologists for many years. Proper recognition of antigen and MHC-restriction by the TCR is necessary for the activation of the T cell. The analysis of the TCR has proved to be a useful tool for the diagnosis of lymphomas and the study of the normal skin immune system. Recently, TCR subset populations were found to be expressed specifically within the epidermis and have been hypothesized to be important in the maintenance of immunity in the skin immune system. In this article, we discuss the relationship of T cells to the immune system and the importance of the TCR to its function and homeostasis.

We have analysed 19 complementary DNA clones encoding the alpha-chain of the T-cell antigen receptor derived from thymic transcripts, and find that 15 of them contain partial or complete variable (V alpha) genes. Seven of these genes cross-hybridize to over 40 germline V alpha gene segments in Southern blot analyses. Of the 19 joining (J alpha) sequences examined, 18 seem to be encoded by distinct gene segments, hence the repertoire of J alpha gene segments is much larger than those of the immunoglobulin or T-cell receptor beta-chain gene families. We suggest that the variable domains of immunoglobulins and T-cell antigen receptors are similar in structure.

A simple and rapid strategy for DNA sequence analysis based on the Sanger chain-termination method is described. This procedure utilizes full-sized inserts of 1 to 4 kb of DNA cloned into M13 bacteriophage vectors. After the sequence of the first 600-650 bp of the insert DNA has been determined with the commercially available universal vector primer, a specific oligonucleotide is synthesized utilizing the sequence data obtained from the 3' end of the sequence and used as a primer to extend the sequence analysis for another 600-650 nucleotides. Additional primers are synthesized in a similar manner until the nucleotide sequence of the entire insert DNA has been determined. General guidelines for the selection of oligonucleotide length and composition and the use of unpurified primers are discussed. The use of the specific-primer-directed approach to dideoxynucleotide sequence analysis, in association with highly purified single-stranded template DNA, reduces considerably the time required for the analysis of large segments of DNA.

The V1 gene encodes the heavy chain variable region of antibodies that bind to phosphorylcholine in the Balb/c mouse. V1 genes have been cloned from mouse sperm DNA, an IgM-producing tumor HPCM2 and an IgA-producing tumor M167. The transcription start site of the V1 gene has been mapped 63 +/- 1 base pairs from the coding sequence for both alpha and mu transcripts. Comparison of flanking DNA sequence 574 base pairs 5' to the V1 transcription start site in sperm, HPCM2 and M167 DNA reveals that sperm and HPCM2 sequences are completely identical in this region and the M167 sequence differs from them by a single base change. Although the coding region of the V1 gene has undergone a high (4%) rate of somatic mutation in M167 we demonstrate that the somatic mutation mechanism stops near the transcription start site. These results demonstrate that initiation of V1 gene transcription remains unchanged with respect to location and 5' sequences throughout B-cell development.

The metabolism of malonaldehyde (MA) was investigated in vivo using male Wistar rats and in vitro using rat liver mitochondria. Twelve hr after intubation with [1,3-14C] MA, 60-70%, 5-15% and 9-17% of administered radioactivity was recovered in expired CO2, feces and urine, respectively. In rats intubated with [1,2-14C) acetate, the corresponding values were 68-82%, 1-2% and 2.3%. 14CO2 evolution was initially slower after 14C-MA administration than after 14C-acetate administration and more radioactivity was excreted in the feces and urine. In vitro experiments using [1,3-14C] MA showed that MA is metabolized primarily in the mitochondria via reactions involving O2 utilization and 14CO2 production. The apparent Km and Vmax were 0.5 mM and 9.3 nmol/min/mg protein for O2 uptake, respectively, and 2.0 mM and 2.4 nmol/min/mg protein for 14CO2 production. Addition of malonic acid to mitochondrial incubates at concentrations inhibitory to succinate dehydrogenase did not affect MA-induced O2 uptake but enhanced 14CO2 production from 14C-MA. 14C-Acetate appeared to be the major accumulating metabolite in rat liver mitochondrial preparations following a 120-min incubation with 14C-MA. A probable biochemical route for MA metabolism involves oxidation of MA by mitochondrial aldehyde dehydrogenase followed by decarboxylation to produce CO2 and acetate.

Groups of growing rats (100-150 g) were offered a choice of two diets, one containing a deficient concentration of phosphorus (0.1%) and the other containing 0.3, 0.6, 1.2 or 1.8% phosphorus. All diets contained 0.6% Ca and were isocaloric. Except for the groups that were offered the 0.1 and 0.3% phosphorus diets, all the animals selected mixtures of diets containing nearly identical phosphorus contents (0.33-0.36%). The group offered the two diets lowest in phosphorus selected 83% of their food from the higher (0.3%) phosphorus diet to obtain a mixture containing 0.25% phosphorus. Irrespective of the phosphorus content of the diets available, all groups ate similar amounts of food, made similar weight gains and maintained normal plasma levels of calcium and phosphorus. The experiment demonstrates the existence of a feedback mechanism by which growing rats regulate their phosphorus intake within narrow limits when allowed to self-select among diets of markedly different phosphorus contents. It is postulated that feedback regulation of phosphorus intake is mediated by changes in plasma calcium homeostasis.

Growing rats offered a choice of four pairs of diets, one low in P (0.1%) and the others containing 0.3, 0.6, 1.2 or 1.8% P, selected food mixtures in each case with nearly identical P contents (0.23-0.24%) (Ca:P = 2.2:1). Mature rats offered the same dietary choices exhibited less rigid diet selection but clearly preferred a diet higher in P (0.64-0.69%) (Ca:P = 0.9:1). Vitamin D-deficient animals selected less P than controls and parathyroidectomized rats severely limited their P intake. The increase in self-determined P consumption relative to Ca in mature rats is consonant with the greater decrease in the requirement for Ca associated with maturation and cessation of bone growth. Susceptibility to hypocalcemia in vitamin D deficiency and parathyroidectomy is a probable factor in the increased sensitivity to excess dietary P, which further depresses plasma Ca. These experiments confirm the existence of a feedback mechanism that regulates the voluntary consumption of P in accordance with physiological needs.

Rats fed vitamin D-deficient diets containing 0.6% Ca and 0.3%, 0.6%, 1.2%, or 1.8% P exhibited progressive increments of hypocalcemia and hyperphosphatemia. In vitro assay of 25-hydroxyvitamin D3-1-alpha-hydroxylase (1-alpha-hydroxylase) activity in isolated kidney cortical mitochondria showed that hyperphosphatemia in the presence of hypocalcemia was associated with an increase in enzyme activity. The results indicate that the stimulation of 1-alpha-hydroxylase associated with depressed plasma Ca in rats fed a high-P diet overrides any inhibition of the enzyme that may be caused by excess plasma phosphate.

It has been postulated that the variable region of the beta-polypeptide of the murine T-cell antigen receptor is encoded by three distinct germ-line gene segments--variable (V beta), diversity (D beta) and joining (J beta)--that are rearranged to generate a V beta gene. Germ-line V beta and J beta gene segments have been isolated previously. Here we report the isolation and characterization of two germ-line D beta gene segments that have recognition signals for DNA rearrangement strikingly similar to those found in the three immunoglobulin gene families and in V beta and J beta gene segments. The D beta and J beta segments can join in the absence of V beta gene segment rearrangement and these rearranged sequences are transcribed in some T cells.

The humoral immune system antigen-binding proteins (immunoglobulins) are disulphide-linked heterodimers of light and heavy chains. The gene for the variable region which determines antigen specificity is assembled when one member from each of the dispersed clusters of variable (V) gene segments, diversity (D) elements (for the heavy chains only) and joining (J) segments rearrange and fuse during B-cell development (reviewed in ref. 1). Short recognition sequences adjacent to these elements appear to be involved in the recombination process. The cellular immune system antigen recognition proteins are receptors on the surface of T cells, which are composed of disulphide-linked alpha-chains and beta-chains, each of which has a variable and constant region. Recently, cDNA clones of the beta-chain mRNA have been isolated; the genomic arrangement is very similar to immunoglobulin genes with multiple V beta genes, and two clusters of J beta segments, each of which is upstream from a constant-region gene segment. The V beta and J beta segments have adjacent recombinational recognition sequences like the immunoglobulin elements. However, approximately 10 nucleotides of the cDNA clones between the V beta and J beta regions were not present in the corresponding genomic elements and may have been due to intervening D beta segments. Here we describe a diversity element (D beta 1.1) in a region of high human-mouse homology about 650 bases 5' to the first J beta cluster. Two transcripts which include sequences upstream of D beta 1.1 are found in the human thymus. This region may have some other function besides providing the beta-chain with a diversity segment.