Anti-idiotype antibodies can induce long-term complete remissions in non-Hodgkin's lymphoma without eradicating the malignant clone

The immunoglobulin on the surface of B-cell lymphomas can be a tumor-specific target for monoclonal antibody therapy. Between 1981 and 1993, 45 individuals with low grade B-cell lymphoma were treated with 52 courses of custom-made anti-idiotype antibodies. The antibodies were used either alone or in combination with alpha-interferon, chlorambucil, or interleukin-2 (IL-2). The majority of these patients responded to treatment, with a 66% overall and 18% complete response rate. Six patients (13%) experienced prolonged complete remissions, five of which are ongoing from 4 to 10 years after therapy and are the subject of this report. We asked whether residual lymphoma could be found in these patients with prolonged remissions. We performed enzyme-linked immunosorbent assay (ELISA) assays for idiotype protein or anti-idiotype antibodies in serum. Blood and bone marrow samples were examined by flow cytometry for idiotype positive cells, and by polymerase chain reaction (PCR) for clonal gene rearrangements of immunoglobulin CDR3 sequences or t(14;18) translocations. Using these sensitive and specific tests it was possible to detect very low levels of residual lymphoma in five of these patients who had been in clinical remission for 3 to 8 years before this evaluation. These five have continued without recurrence for up to 3 years since. Thus, we have found a pattern of residual inactive disease in patients treated with anti-idiotype antibodies. The biology of follicular lymphoma evidently includes the potential for tumor dormancy after therapies with varied mechanisms of action, resulting in clinical inactivity for many years. Thus, long-term control of the disease is possible at a clinical level despite persistence of the malignant clone.

Amino acid metabolism and the energetics of growth

The nonessential amino acids are involved in a large number of functions that are not directly associated with protein synthesis. Recent studies using a combination of transorgan balance and stable isotopic tracers have demonstrated that a substantial portion of the extra-splanchnic flux of glutamate, glutamine, glycine and cysteine derives from tissue synthesis. A key amino acid in this respect is glutamic acid. Little glutamic acid of dietary origin escapes metabolism in the small intestinal mucosa. Furthermore, because glutamic acid is the only amino acid that can be synthesized by mammals by reductive amination of a ketoacid, it is the ultimate nitrogen donor for the synthesis of other nonessential amino acids. Because the synthesis of glutamic acid and its product glutamine involve the expenditure of adenosine triphosphate (ATP), it seems possible that nonessential amino acid synthesis might have a significant bearing on the energetics of protein synthesis and, hence, of protein deposition. This paper discusses the topic of the energy cost of protein deposition, considers the metabolic physiology of amino acid oxidation and nonessential amino acid synthesis, and attempts to combine the information to speculate on the overall impact of amino acid metabolism on the energy exchanges of animals.

Advances in the management of Hodgkin's and non-Hodgkin's lymphoma

Recent developments in the management of lymphoma continue to refine our approach to the disease. There is increasing acceptance of the International Lymphoma Study Group classification for non-Hodgkin's lymphoma. Identification of a new viral agent associated with certain subtypes of lymphoma and new immunologic therapies change our perspective on the disease. New data on treatment results further elucidate the role of radiotherapy and high-dose therapy in Hodgkin's disease and the non-Hodgkin's lymphomas.

Phorbol esters induce differentiation of human CD34+ hemopoietic progenitors to dendritic cells: evidence for protein kinase C-mediated signaling

The intracellular signals that mediate the differentiation of pluripotent hemopoietic progenitors to dendritic cells (DC) are largely undefined. We have found that the phorbol ester PMA by itself induced 47% +/- 8.7% of input human CD34+ hemopoietic progenitors to differentiate into cells with morphology and surface Ag phenotype characteristic of DC by day 7 of culture. Functionally, PMA-generated DC processed and presented whole soluble Ag and also induced resting T cell proliferation and Ag-specific CTL effector function. Unlike cytokine-driven DC differentiation, PMA suppressed proliferation and induced cell death (in part via apoptosis) in cells that did not differentiate to DC. The effects of PMA were blocked by inhibitors of protein kinase C activation, suggesting a central role for this signaling molecule. PMA-mediated signaling also induced expression of the RelB transcription factor, an NF-kappaB family member implicated in DC differentiation. These findings suggest that phorbol esters activate protein kinase C, which then initiates the terminal component of an intracellular signaling pathway(s) involved in the DC differentiation of CD34+ hemopoietic progenitors.

Phorbol Esters Induce Differentiation of Human CD34+ Hemopoietic Progenitors to Dendritic Cells: Evidence for Protein Kinase C-Mediated Signaling

The intracellular signals that mediate the differentiation of pluripotent hemopoietic progenitors to dendritic cells (DC) are largely undefined. We have found that the phorbol ester PMA by itself induced 47% ± 8.7% of input human CD34+ hemopoietic progenitors to differentiate into cells with morphology and surface Ag phenotype characteristic of DC by day 7 of culture. Functionally, PMA-generated DC processed and presented whole soluble Ag and also induced resting T cell proliferation and Ag-specific CTL effector function. Unlike cytokine-driven DC differentiation, PMA suppressed proliferation and induced cell death (in part via apoptosis) in cells that did not differentiate to DC. The effects of PMA were blocked by inhibitors of protein kinase C activation, suggesting a central role for this signaling molecule. PMA-mediated signaling also induced expression of the RelB transcription factor, an NF-κB family member implicated in DC differentiation. These findings suggest that phorbol esters activate protein kinase C, which then initiates the terminal component of an intracellular signaling pathway(s) involved in the DC differentiation of CD34+ hemopoietic progenitors.

Inhibition of human mast cell growth and differentiation by interferon gamma-1b

In an effort to identify cytokines that inhibit human mast cell growth, we cultured HMC-1 cells and recombinant human stem cell factor (rhSCF)-dependent human bone marrow-derived mast cells (HBMCs) in the presence of interferon gamma (IFNgamma)-1b and interferon alpha (IFNalpha)-2b. HMC-1 cell numbers decreased in the presence of 1000 U/mL IFNgamma-1b but were unaffected by 1000 U/mL of IFNalpha-2b. HBMCs were then cultured for 0 to 7 days with 100 ng/mL rhSCF and 10 ng/mL recombinant human IL-3 (rhIL-3), followed by culture in rhSCF and administration of either 1000 U/mL IFNalpha-2b or 1000 U/mL IFNgamma-1b. HBMCs appearing in cultures with rhSCF alone or in combination with IFNalpha-2b were virtually identical in number through 8 weeks of culture. In cultures supplemented with IFNgamma-1b, HBMCs significantly decreased in number and incidence of granular metachromasia by 4 to 5 weeks (p<0.001). Similar results were obtained when human marrow was cultured from day 0 with rhSCF and IFNgamma-1b. Mature rhSCF-dependent HBMCs were also cultured at 5 weeks with rhSCF alone or in combination with IFNgamma-1b. Compared with cells cultured in rhSCF, mature 5-week HBMC cultures treated with rhSCF plus IFNgamma-1b revealed a decrease in mast cells, and those mast cells that remained had fewer toluidine blue- and tryptase-positive granules after 5 to 8 weeks. FACS analysis of rhSCF plus IFNgamma-1b-treated mature HBMCs revealed increased c-kit and Fc(epsilon)RI expression. Mast cell releasibility was not increased. IFNgamma-lb was thus able to suppress mast cell growth from CD34+ cells, suggesting that this agent should be considered as a candidate cytokine for the treatment of disorders of mast cell proliferation.

Roles of insulin and amino acids in the regulation of protein synthesis in the neonate

Neonates deposit protein at a very high rate and efficiently utilize dietary amino acids for protein deposition. This high efficiency is associated with an elevated stimulation of tissue protein synthesis by feeding. Our recent studies have focused on identification of the factors that mediate this response in the neonate. A positive curvilinear relationship between skeletal muscle protein synthesis and plasma insulin concentration was identified in fasted and fed suckling pigs; the relationship changes with development. To test the specific effects of insulin on protein metabolism in the neonate, a procedure to clamp amino acids, under hyperinsulinemic conditions, was developed. By using this technique, we showed that insulin-stimulated whole-body amino acid disposal is elevated in the neonate, and this response may account for the efficient use of dietary amino acids for protein accretion. More recent studies suggest that the enhanced stimulation of skeletal muscle protein synthesis by feeding in the neonate is primarily insulin mediated; however, the stimulation of liver protein synthesis by feeding seems to be largely a function of amino acid concentration.

Free amino acids in milks of human subjects, other primates and non-primates

Preterm and term transitional milks of human subjects and mature milks of human subjects, non-human primates and non-primates were analysed for free amino acids (AA) using precolumn phenylisothiocyanate derivatization and liquid chromatography. Differences in free AA between three types of human milk were small. Milks of pinnipeds (seals and sea lions) contained the highest levels of total free AA (8634-20,862 mumol/l), while the milks of cows and sheep had the lowest levels of total free AA (1061-1357 mumol/l). The milks of human subjects, chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla), elephants (Elephas maximus), horses and pigs had intermediate levels of total free AA (3069-7381 mumol/l). Glutamic acid was the most abundant free AA in milks of human subjects (1339-2157 mumol/l), non-human primates (423-2528 mumol/l), elephants (1332 mumol/l), horses (1119 mumol/l), and cows (349 mumol/l). Taurine was the most abundant free AA in milks of pinnipeds (5776-13,643 mumol/l), pigs (1238 mumol/l), goats (1150 mumol/l) and sheep (341 mumol/l). Taurine was the second most abundant free AA in milks of human subjects and non-human primates, while histidine was the second most abundant free AA in milks of pinnipeds. Milks of each species had a distinctive free AA pattern which may reflect the relative importance of the free AA during early postnatal development.

Exogenous growth hormone stimulates somatotropic axis function and growth in neonatal pigs

We studied the effects of exogenous porcine growth hormone (pGH) administration on circulating insulin-like growth factor I (IGF-I) concentration, IGF-binding proteins (IGFBP), tissue growth, and protein synthesis in neonatal pigs. One-day-old pigs were given daily intramuscular injections of either pGH (1 mg/kg body wt) (n = 6) or saline (n = 5) for 7 days, after which time we measured in vivo protein synthesis using a bolus of [3H]-phenylalanine. Mean plasma pGH concentration in pGH-treated pigs measured on day 7 was 22-fold higher than in controls. The plasma IGF-I concentration in pGH-treated pigs was significantly greater than in controls after 1 day of treatment and plateaued at 285% of control values after 4 days. After 7 days of treatment, plasma IGFBP-3 concentrations and the plasma glucose response to a meal were also greater in pGH-treated than control pigs. pGH treatment significantly increased body weight gain and food conversion efficiency and the protein synthesis rate in several visceral organs. Our results demonstrate that exogenous pGH increases circulating IGF-I and IGFBP-3 concentrations and visceral organ growth in neonatal pigs, suggesting that the somatotrophic axis is functional in the neonate.

Role of milk-borne vs endogenous insulin-like growth factor I in neonatal growth

Neonatal pigs are characterized by a high efficiency of nutrient utilization and rapid growth rate. The utilization of dietary protein for lean tissue growth is particularly efficient in neonatal pigs and is associated with a high rate of skeletal muscle protein synthesis and deposition. In support of these high growth rates, neonatal pigs consume a milk diet that has a high biological value and is abundant in growth factors, including insulin and IGF-I. During the neonatal period, there are developmental changes in the circulating concentrations of, and tissue responsiveness to, hormones, particularly insulin, IGF-I, and growth hormone that play a central role in growth regulation. Our goal has been to characterize the dietary factors and specific aspects of endocrine function that are responsible for the anabolic stimulus that helps to sustain the high rates of protein deposition in neonatal pigs. Our results suggest that, despite the abundance of growth factors in milk and colostrum, the intake of nutrients is the primary anabolic stimulus for protein synthesis and this response declines with age. There is, however, a nonnutritive and as-yet-unidentified component in colostrum that provides a specific anabolic stimulus for skeletal muscle in newborns, but this is probably neither insulin nor IGF-I. Our studies also indicate that circulating concentration of IGF-I are not a primary stimulus of skeletal muscle protein synthesis and that the primary endocrine signal that mediates the response to nutrient intake may be insulin. Future research should address how the local expression of IGF and the function of insulin and IGF receptors affect the responsiveness of anabolic processes to nutrient intake and hence the efficiency of neonatal growth.

Human mast cells produce the CD4+ T lymphocyte chemoattractant factor, IL-16

CD4+ T cell infiltration is known to occur in tissues at sites of mast cell activation. The molecules produced and released by mast cells that account for this lymphocyte accumulation are poorly characterized. Here we report that a CD4+ T cell chemoattractant cytokine, IL-16, is stored preformed in bone marrow-cultured human mast cells and a human mast cell line, HMC-1, as demonstrated by intracytoplasmic cytokine staining and flow cytometry, and in human lung mast cells, as detected by immunohistochemistry. In response to the anaphylatoxin, C5a, or to PMA treatment, IL-16 mRNA transcripts detected by Northern blot analysis in HMC-1 cells increased 6- to 10-fold. HMC-1 cell lysates and activated supernatants contained IL-16 protein, as demonstrated by both ELISA and in vitro lymphocyte chemotaxis assays, the latter of which was blocked 59 to 88% by the addition of neutralizing Ab to recombinant human IL-16. IL-16 bioactivity was detected in the supernatants 2 to 4 h after PMA or C5a activation, and this activity remained elevated through 24 h. The capacity of human mast cells to synthesize and release biologically active IL-16 provides a possible link between mast cell activation and the accumulation of T cells in mast cell-dependent inflammation, thus amplifying the immune response and perpetuating the pathologic process.

Human mast cells produce the CD4+ T lymphocyte chemoattractant factor, IL-16

CD4+ T cell infiltration is known to occur in tissues at sites of mast cell activation. The molecules produced and released by mast cells that account for this lymphocyte accumulation are poorly characterized. Here we report that a CD4+ T cell chemoattractant cytokine, IL-16, is stored preformed in bone marrow-cultured human mast cells and a human mast cell line, HMC-1, as demonstrated by intracytoplasmic cytokine staining and flow cytometry, and in human lung mast cells, as detected by immunohistochemistry. In response to the anaphylatoxin, C5a, or to PMA treatment, IL-16 mRNA transcripts detected by Northern blot analysis in HMC-1 cells increased 6- to 10-fold. HMC-1 cell lysates and activated supernatants contained IL-16 protein, as demonstrated by both ELISA and in vitro lymphocyte chemotaxis assays, the latter of which was blocked 59 to 88% by the addition of neutralizing Ab to recombinant human IL-16. IL-16 bioactivity was detected in the supernatants 2 to 4 h after PMA or C5a activation, and this activity remained elevated through 24 h. The capacity of human mast cells to synthesize and release biologically active IL-16 provides a possible link between mast cell activation and the accumulation of T cells in mast cell-dependent inflammation, thus amplifying the immune response and perpetuating the pathologic process.

CTLA4-Ig and anti-CD40 ligand prevent renal allograft rejection in primates

Selective inhibition of T cell costimulation using the B7-specific fusion protein CTLA4-Ig has been shown to induce long-term allograft survival in rodents. Antibodies preventing the interaction between CD40 and its T cell-based ligand CD154 (CD40L) have been shown in rodents to act synergistically with CTLA4-Ig. It has thus been hypothesized that these agents might be capable of inducing long-term acceptance of allografted tissues in primates. To test this hypothesis in a relevant preclinical model, CTLA4-Ig and the CD40L-specific monoclonal antibody 5C8 were tested in rhesus monkeys. Both agents effectively inhibited rhesus mixed lymphocyte reactions, but the combination was 100 times more effective than either drug alone. Renal allografts were transplanted into nephectomized rhesus monkeys shown to be disparate at major histocompatibility complex class I and class II loci. Control animals rejected in 5-8 days. Brief induction doses of CTLA4-Ig or 5C8 alone significantly prolonged rejection-free survival (20-98 days). Two of four animals treated with both agents experienced extended (>150 days) rejection-free allograft survival. Two animals treated with 5C8 alone and one animal treated with both 5C8 and CTLA4-Ig experienced late, biopsy-proven rejection, but a repeat course of their induction regimen successfully restored normal graft function. Neither drug affected peripheral T cell or B cell counts. There were no clinically evident side effects or rejections during treatment. We conclude that CTLA4-Ig and 5C8 can both prevent and reverse acute allograft rejection, significantly prolonging the survival of major histocompatibility complex-mismatched renal allografts in primates without the need for chronic immunosuppression.

Insulin-stimulated amino acid utilization during glucose and amino acid clamps decreases with development

Neonatal animals utilize their dietary amino acids for protein accretion with high efficiency, and this efficiency declines during early life. The factors responsible for this developmental change are unknown. Our objectives were to determine whether amino acid (AA) utilization is stimulated by insulin in the neonate and whether this response changes during the suckling period. Two hyperinsulinemic-euglycemic clamp infusion studies, using 10-2,000 ng insulin.kg-0.66.min-1, were performed in 7- and 26-day-old pigs. In study I, no AA were provided during the infusion, and the resultant decline in plasma AA levels was defined. In study II, plasma AA were clamped at near-fasting levels, and whole body utilization of exogenous AA was determined by measuring the rate of infusion of an AA mixture necessary to maintain basal plasma lysine concentrations. In study I, the half-maximal effective dose (ED50) for the fall in AA concentrations with increasing plasma insulin concentration was lower in 7- than in 26-day-old pigs, and the nadir in AA concentration was achieved by only 20 microU/ml insulin. In study II, the utilization of exogenous AA during hyperinsulinemic-euglycemic AA clamps exhibited a higher maximum response (Rmax) (49 vs. 26 mumol AAtotal.min-1.kg-1) and a lower ED50 (18 vs. 45 microU insulin/ml) in 7- than in 26-day-old pigs. Plasma urea nitrogen concentrations did not rise with increasing insulin and AA infusion rates. These results indicate that insulin stimulates the utilization of exogenous AA in neonatal pigs and that both the insulin sensitivity and responsiveness of AA utilization decline over the suckling period. The infused AA were likely utilized for protein accretion.

Exogenous insulin-like growth factor-I increases weight gain in intrauterine growth-retarded neonatal pigs

Many cases of intrauterine growth retardation (IUGR) are the result of placental insufficiency, suggesting that potential therapies should focus on the neonate rather than the pregnant female. We wished to determine whether IGF-I could be used therapeutically to stimulate normal rates of growth in these neonates. Eight sows received 2.3 kg/d of either a control (13% protein) or protein-restricted (0.5% protein) diet from d 63 of pregnancy to parturition. Litters were reduced to 6 pigs at 3 d of age, and IUGR neonates were fostered onto a control sow. Three pigs/ litter received an osmotic minipump containing either saline or recombinant human IGF-I, delivered at 4 microg/h from d 3 to d 10 of age. Tissue protein synthesis was measured in all pigs using a flooding dose of [3H]phenylalanine. At birth, both body weight (10%) and circulating IGF-I concentration (30%) were significantly lower in IUGR than in control newborns. The infusion of IGF-I to IUGR neonates significantly increased the circulating concentration of IGF-I, growth rate, and protein and fat accretion to control levels. The infusion of IGF-I did not alter concentrations of insulin, glucose, IGF-II, or the thyroid hormones. Our results suggest that IGF-I may be a potential therapy to restore normal growth in IUGR infants.

Colostrum enhances the nutritional stimulation of vital organ protein synthesis in neonatal pigs

Our objective was to determine the relative importance of the macronutrient components of colostrum in the stimulation of vital organ protein synthesis in neonatal pigs. We studied colostrum-deprived newborn pigs within 4-6 h after birth (unfed) and three groups fed for 24 h mature milk, colostrum, or a formula containing a macronutrient composition comparable to that of colostrum. We measured protein synthesis in vivo using a flooding dose of 3H-phenylalanine. The fractional rates of protein synthesis (Ks) in the brain, heart, lung, kidney and spleen were significantly higher in all fed groups than in the unfed newborns. Among the three fed groups, brain and heart protein synthesis rates were greater in colostrum-fed than in either milk- or formula-fed pigs. Kidney and spleen protein synthesis rates in colostrum- and formula-fed pigs were not significantly different, but both were higher than in milk-fed pigs. The stimulation of kidney protein synthesis in response to feeding was primarily a consequence of greater protein synthetic efficiency; however, protein synthetic capacity in the heart, lung and spleen was generally greater in colostrum- and formula-fed pigs than in unfed newborns. Our results suggest that the predominant stimulus for vital organ protein synthesis in colostrum-fed neonatal pigs is nutrient intake. However, there was a specific stimulation of both brain and heart protein synthesis in colostrum-fed pigs that cannot be attributed to macronutrients.

Food intake alters muscle protein gain with little effect on Na(+)-K(+)-ATPase and myosin isoforms in suckled rats

Biochemical maturation accompanies the rapid accretion of skeletal muscle in early life. We wished to determine whether changes in muscle protein accretion, induced by variations in food intake, altered the biochemical maturation of the soleus and the extensor digitorum longus (EDL) muscles. Rat pups were suckled in litters of 4, 10, or 16 to induce differences in food intake. At 21 days of age, muscle protein and DNA were quantitated and biochemical maturation was assessed from measurement of [3H]ouabain-binding site abundance and myosin isoform composition. Differences in food intake produced a twofold range in body and muscle weights and protein and DNA contents. Protein accretion was more sensitive to nutrient intake in the soleus than in the EDL. Serum 3-5,3'-triiodothyronine (T3) and insulin concentrations decreased with a reduction in food intake. Total ouabain-binding sites were not altered in either muscle and were independent of muscle size. Differences in myosin isoform composition were more pronounced for the soleus than the EDL, but were relatively small in magnitude. These results demonstrate that, whereas postnatal muscle protein accretion and circulating hormone concentrations are sensitive to food intake, the biochemical maturation is resilient. The immature muscle does not exhibit the fiber type-specific responses to malnutrition typical of mature muscle.

Intrauterine growth restriction does not alter response of protein synthesis to feeding in newborn pigs

This study aimed to determine the effect of intrauterine growth restriction (IUGR) on the acute response of tissue protein synthesis to feeding in newborn pigs. Newborn pigs of sows fed either control or protein-restricted diets throughout gestation were designated C or IUGR, respectively. Both groups were either fasted for 9 h after birth or fed hourly 30 ml colostrum/kg body wt for 2.75 h after a 6-h fast. Fractional rates of tissue protein synthesis (Ks) were measured in vivo with a flooding dose of L-[4-3H]phenylalanine. Birth weight was reduced by 33% in IUGR pigs. IUGR had no effect on Ks in skeletal muscles, heart, liver, jejunum, or pancreas. Feeding stimulated tissue Ks similarly in C and IUGR pigs. Fasting plasma insulin concentrations and their rise with feeding were unaffected by IUGR. Plasma insulin-like growth factor I (IGF-I) concentrations were reduced by 42% in IUGR pigs and were not altered by feeding in either IUGR or C pigs. There were positive nonlinear relationships between tissue Ks and circulating concentrations of insulin. The results indicate that, in newborn pigs, tissue Ks are unaffected by IUGR, despite reduced plasma IGF-I concentrations. The efficiency with which nutrients stimulate tissue Ks is also not altered by IUGR, perhaps because the rise in plasma insulin concentrations with feeding is unaffected by IUGR.

Conditioned medium from primary porcine endothelial cells alone promotes the growth of primitive human haematopoietic progenitor cells with a high replating potential: evidence for a novel early haematopoietic activity

The authors have recently shown that direct contact with primary porcine microvascular endothelial cell monolayers (PMVECs) in combination with haematopoietic growth factors enhances the expansion of primitive human haematopoietic CD34+ bone marrow progenitor cells. It is now demonstrated that serum-free conditioned medium (PMVEC CM, concentrated 70x for proteins >30 kDa) from untreated PMVECs contains haematopoietic growth factor activity that enhances the in vitro proliferation, haematopoietic cell production, and colony cell formation of primitive human haematopoietic progenitor cells. In combination with exogeneously added human growth factors such as interleukin 3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF) and EPO, PMVEC CM enhances the proliferation and colony growth of human haematopoietic CD34+ cells. In contrast, PMVEC CM has no significant synergistic activity on either stem cell factor (SCF) or flt3-ligand-induced CD34+ cell proliferation, cell production or colony formation. Blocking mAbs against the c-kit receptor have no effect on PMVEC CM-induced CD34+ cell proliferation at titres that completely suppress SCF-induced proliferation. Moreover, it is shown that this haematopoietic growth factor supports the proliferation and colony formation of murine, non-human primate, and porcine marrow progenitor cells without any apparent species-specific restrictions in its activity. These finding suggest that PMVEC CM contains a novel early haematopoietic activity.

Mitogenic stimulation of T cells reveals differing contributions for B7-1 (CD80) and B7-2 (CD86) costimulation

The requirement of accessory cells for concanavalin A (Con A) activation of T cells suggests delivery of a separate costimulatory signal. However, the costimulatory pathways involved have not been identified. These studies assess the role of CD28-B7-mediated costimulation during T-cell activation by Con A. The B7-1/B7-2 binding protein CTLA4-Ig inhibited the proliferative response of primary lymph node cells to either Con A or soluble anti-CD3 mAb. This suppression was dose dependent and could be reversed by CD28 cross-linking. CTLA4-Ig also completely suppressed induction of interleukin-2 (IL-2) mRNA by Con A. CTLA4-Ig-mediated suppression was not due to blockade of the Con A 'receptor(s)' or of the primary activation signal (as measured by the intracellular calcium response). Although both B7-1 and B7-2 were up-regulated following Con A activation, each played a different role in proliferation and cytokine production. Individually, anti-B7-2 Fab partially inhibited the Con A response whereas anti-B7-1 Fab had no effect. However, the combination of anti-B7-1 and anti-B7-2 Fab completely suppressed proliferation and IL-2 production. Therefore, while a part of the Con A response requires B7-2, the remainder of the response can utilize either B7-1 or B7-2. Together, these results demonstrate that Con A activation of T cells requires the delivery of a separate costimulatory signal that is mediated almost entirely by the B7 receptors.

Molecular cloning and characterization of CFT1, a developmentally regulated avian alpha(1,3)-fucosyltransferase gene

Although coordinate expression of carbohydrate epitopes during development is well described, mechanisms which regulate this expression remain largely unknown. In this study we demonstrate that developing chicken B cells express the LewisX terminal oligosaccharide structure in a stage-specific manner. To examine regulation of this expression, we have cloned and expressed the chicken alpha(1,3)-fucosyltransferase gene involved in LewisX biosynthesis, naming it chicken fucosyltransferase 1 (CFT1). CFT1 is characterized by a single long open reading frame of 356 amino acids encoding a type II transmembrane glycoprotein. The domain structure and predicted amino acid sequence are highly conserved between CFT1 and mammalian FucTIV genes (52.8% and 46.3% identity to mouse and human respectively). In vitro CFT1 fucosyltransferase activity utilizes LacNAc > 3'sialyl-LacNAc acceptors with almost no utilization of other neutral type II (lactose, 2-fucosyllactose), or type I (lacto-N-biose I) acceptors. CFT1-transfected cells make cell surface LewisX (COS-7) and LewisX + VIM-2 structures (Chinese hamster ovary). CFT1 gene expression is tissue-specific and includes embryonic thymus and bursa. Furthermore, expression of the CFT1 gene and cell surface LewisX structures are closely linked during B cell development. These findings reveal the evolutionary conservation between nonmammalian and mammalian alpha(1,3)-fucosyltransferase genes and demonstrate a role for fucosyltransferase gene regulation in the developmental expression of oligosaccharide structures.

CTLA-4 blockade enhances clinical disease and cytokine production during experimental allergic encephalomyelitis

The B7 family of cell surface molecules expressed on APC provides accessory signals to T cells via either CD28 or CTLA-4. However, while CD28 transduces a costimulatory signal that is required for an optimal immune response, CTLA-4 transmits a negative signal. These studies use an anti-CTLA-4 mAb to directly address the role of this T cell surface molecule in experimental allergic encephalomyelitis (EAE). CTLA-4 regulation of disease was assessed during initial immune cell interactions and during the effector stage of the encephalitogenic immune response. The effects of anti-CTLA-4 treatment were schedule dependent. CTLA-4 blockade during the onset of clinical symptoms markedly exacerbated disease, enhancing mortality. Disease exacerbation was associated with enhanced production of the encephalitogenic cytokines TNF-alpha, IFN-gamma and IL-2. Hence, CTLA-4 regulates the intensity of the autoimmune response in EAE, attenuating inflammatory cytokine production and clinical disease manifestations.

CTLA-4 blockade enhances clinical disease and cytokine production during experimental allergic encephalomyelitis

The B7 family of cell surface molecules expressed on APC provides accessory signals to T cells via either CD28 or CTLA-4. However, while CD28 transduces a costimulatory signal that is required for an optimal immune response, CTLA-4 transmits a negative signal. These studies use an anti-CTLA-4 mAb to directly address the role of this T cell surface molecule in experimental allergic encephalomyelitis (EAE). CTLA-4 regulation of disease was assessed during initial immune cell interactions and during the effector stage of the encephalitogenic immune response. The effects of anti-CTLA-4 treatment were schedule dependent. CTLA-4 blockade during the onset of clinical symptoms markedly exacerbated disease, enhancing mortality. Disease exacerbation was associated with enhanced production of the encephalitogenic cytokines TNF-alpha, IFN-gamma and IL-2. Hence, CTLA-4 regulates the intensity of the autoimmune response in EAE, attenuating inflammatory cytokine production and clinical disease manifestations.

Spectrophometric assay for measuring branched-chain amino acid concentrations: application for measuring the sensitivity of protein metabolism to insulin

Plasma amino acid concentrations fall during insulin infusion. Amino acid concentrations can be maintained using an infusion of amino acids if their plasma concentration can be determined within a few minutes. We developed a spectrophometric assay which determines the total concentration of all three branched-chain amino acids in plasma within 1 min. The enzyme leucine dehydrogenase oxidatively deaminates leucine, isoleucine, and valine, with stoichiometric reduction of NAD that is measured using a spectrophotometer. The assay was developed in both a kinetic and end-point format. For the kinetic assay the buffer conditions were formulated to obtain equivalent rates with all three amino acids so that it could be used in samples containing unknown mixtures. For the end-point assay additional enzyme was added so that an end-point could be reached within 1 min. The application of the kinetic assay for "clamping" the branched-chain amino acids during hyperinsulinemic euglycemic clamps in humans is demonstrated.

Effect of spaceflight on human stem cell hematopoiesis: suppression of erythropoiesis and myelopoiesis

Humans subjected to periods of microgravity develop anemia, thrombocytopenia, and abnormalities in red blood cell structure. The causes of these abnormalities are complex and unclear. The in vitro effects of spaceflight on hematopoietic cell proliferation and differentiation were investigated during the space shuttle missions STS-63 (Discovery) and STS-69 (Endeavour). CD34+ bone marrow progenitor cells were cultured in liquid suspension culture and on hematopoietic supportive stromal cells using hollow-fiber culture modules. One set of cultures was maintained at microgravity (flight cultures) for the last 8-10 days of culture and a second control was at full gravity (ground control). Over the 11- to 13-test-day period, ground control culture total cell number increased 41.0- to 65.5-fold but flight culture total cell number increased only 10.1- to 17.6-fold (57-84% decrease). Comparing ground control cultures and microgravity cultures, respectively, for progenitor cell content, myeloid progenitor cell numbers expanded 2.6- to 17.5-fold compared with 0.9- to 7.0-fold and erythroid progenitor cell numbers expanded 2.0- to 4.1-fold in ground control cultures but actually declined at microgravity (>83% reduction). Moreover, microgravity cultures demonstrated accelerated maturation/differentiation toward the macrophage lineage. These data indicate that spaceflight has a direct effect on hematopoietic progenitor cell proliferation and differentiation and that specific aspects of in vitro hematopoiesis, particularly erythropoiesis, involve gravity-sensitive components.

Primary porcine endothelial cells express membrane-bound B7-2 (CD86) and a soluble factor that co-stimulate cyclosporin A-resistant and CD28-dependent human T cell proliferation

Increasing evidence suggests that endothelial cells can directly activate syngeneic, allogeneic and xenogeneic T cells. In this study we demonstrate that unstimulated, paraformaldehyde-fixed primary porcine aortic endothelial cells (PAEC) and microvascular endothelial cells (PMVEC) can provide co-stimulation for human T cell IL-2 secretion and proliferation. EC-mediated co-stimulation has both cyclosporin A (CsA)-sensitive and CsA-resistant components. The CsA-resistant component is completely suppressed either by blocking with anti-CD28 F(ab) fragments or CTLA-4-Ig. Northern blot analysis of unstimulated PAEC and PMVEC with porcine-specific probes reveals constitutive expression of B7-2 mRNA while B7-1 message was not detected. hCTLA-4-Ig and anti-B7-2 mAb immunoprecipitates a single 79 kDa PMVEC surface protein. Surprisingly, PMVEC conditioned media also has soluble co-stimulatory activity that is blocked by anti-CD28 F(ab) fragments or anti-B7-2 mAb. These findings demonstrate that primary unstimulated porcine EC can co-stimulate CsA-resistant human T cell proliferation through binding of membrane bound, constitutively expressed EC B7-2 (CD86) to human T cell CD28, providing one of the first demonstrations of functional B7-2 on cells outside the immune system. In addition, PMVEC secrete or shed a soluble factor that mediates CD28-dependent human T cell proliferation, demonstrating the existence of soluble mediators of CD28 activation.

Whole-body protein turnover in the fed state is reduced in response to dietary protein restriction in lactating women

We examined the adaptive responses of body protein metabolism in the fed state to dietary protein restriction in lactating women to determine whether rates of body protein degradation and synthesis were lower than those of nonlactating women. Thirteen healthy women (five lactating, four nonlactating postpartum, four nulliparous) aged 28-32 y were given protein intakes of 1.5, 0.4, and 1.0 g.kg-1.d-1 over three consecutive 3-d periods, respectively. At the end of each period, while in the fed state, subjects received orally a single bolus dose of [1-13C]leucine. A 24-h urine collection was obtained simultaneously. Whole-body protein metabolism was characterized by using the end product model based on nitrogen excretion and leucine catabolism. Nitrogen flux and rates of protein degradation and synthesis in the fed state were significantly lower at a dietary protein intake of 1.0 g.kg-1.d-1 in lactating women than in their nonlactating postpartum counterparts. Net protein retention in the fed state was significantly higher at a dietary protein intake of 1.0 g.kg-1.d-1 in lactating than in nonlactatating postpartum and nulliparous women because of the relatively greater reduction in protein degradation than in protein synthesis. These studies suggest that lactating women rapidly adapt to dietary protein restriction by down-regulating protein metabolism, and that 13C-labeled amino acid tracers in combination with urinary nitrogen excretion serve as useful metabolic markers for the adequacy of the dietary protein content of lactating women.

Orally administered IGF-I increases intestinal mucosal growth in formula-fed neonatal pigs

Our objective was to determine the potentially anabolic effects of orally administered recombinant human insulin-link growth factor I (rhIGF-I)on small intestinal growth in formula-fed neonatal pigs. Unsuckled neonatal pigs received formula or formula containing added rhIGF-I (3.5 mg.kg-1.day-1) from birth to 4 days of age. Pigs in both groups were fed 30 ml/kg formula every 2 h on day 1 and then every 4 h on days 2-4, and blood was sampled daily. Oral administration of rhIGF-I to formula-fed neonatal pigs increased small intestinal weight, protein, and DNA content,but not length. Jejunal and ileal villus height, but not crypt depth or muscularis thickness, also were increased by oral rhIGF-I administration. Neither the circulating concentration of IGF-I nor the IGF-binding proteins differed between control and oral rhIGF-treated pigs, suggesting that the absorption of orally administered rhIGF-I from the intestinal lumen into the peripheral circulation was limited. Our results demonstrate that oral administration of rhIGF-I during the first 4 days after birth significantly increased small intestinal mucosal growth in formula-fed neonatal pigs. These results suggest that oral administration of rhIGF-I may be a viable therapeutic approach to enhance intestinal growth in neonates.

Protein synthesis in skeletal muscle and jejunum is more responsive to feeding in 7-than in 26-day-old pigs

The study aimed to determine the developmental changes in the response of peripheral and visceral tissue protein synthesis to feeding during early postnatal life and the associated changes in circulating insulin, insulin-like growth factor (IGF-I), and amino acid concentrations. Tissue protein synthesis was measured in vivo with a large dose of L-[4(-3)H]phenylalanine in 7- and 26-day-old pigs that were either fasted for 24 h or refed for 2.75 h after a 24-h fast. Fractional rates of protein synthesis (Ks) in skeletal muscle, heart, and liver were greater in 7-than in 26-day-old pigs. Refeeding stimulated Ks in skeletal muscle, pancreas, jejunum, and liver of both 7-and 26-day-old pigs. The stimulation of skeletal muscle and jejunal Ks by refeeding was greater in 7- than in 26-day-old pigs. Plasma IGF-I concentrations were lower in 7- than in 26-day-old pigs. Plasma concentrations of insulin and amino acids increased with refeeding. The increase in plasma insulin concentrations with refeeding was greater in 7- than in 26-days-old pigs. These results indicate that the stimulation in skeletal muscle and jejunal protein synthesis by feeding is elevated in young compared with older suckling pigs. This enhanced stimulation of protein synthesis by feeding in neonatal pigs is associated with elevated circulating concentrations of insulin but not amino acids or IGF-I.

Corticosterone has independent effects on tissue maturation and growth in the suckling rat

Glucocorticoids are associated with reduced weight gain when used to improve pulmonary function in premature infants. However, tissue maturation is stimulated during normal development by an increase in serum glucocorticoids. We evaluated the effects of glucocorticoid treatment on tissue weight gain and the activity of specific enzymes in the suckling rat, with the hypothesis that these processes are independently regulated. Before the ontogenic surge in corticosterone, 6-d-old rat pups were implanted with a pellet to release corticosterone continuously at 0 (placebo), 48, 120, 240, or 360 micro g/d. We killed the pups at 7, 9, or 12 d of age and measured tissue weights and activities of sucrase and glutamine synthetase. Serum corticosterone concentrations were elevated with dose. Tissue weight gain was proportional to ln(e) serum corticosterone at all ages. In contrast, enzyme indices of tissue maturation did not respond to corticosterone until d9. Also, intestinal tissue was more sensitive than muscle to the effects of corticosterone on weight but less sensitive to its effects on maturation. We conclude that the immediate response, in terms of weight versus the delayed response of the enzymes and their reciprocal sensitivity in muscle and gut, indicates that these processes are independently regulated.

Opposing effects of CTLA4-Ig and anti-CD80 (B7-1) plus anti-CD86 (B7-2) on experimental allergic encephalomyelitis

The roles of the B7 receptors, CD80 and CD86, during actively induced experimental allergic encephalomyelitis were examined with specific monoclonal antibodies and CTLA4-Ig. Injection of CTLA4-Ig on day 2 post-immunization resulted in decreased incidence and severity of resultant disease. Anti-CD80 injection on day 2 blocked development of the first disease episode. Subsequent relapses were unaffected. In contrast, injection of anti-CD86 alone had no effect. Surprisingly, combined anti-CD80 + anti-CD86 monoclonal antibody injection on day 2 resulted in marked exacerbation of disease. Examination of cytokine production in the draining lymph node cells demonstrated a reduction in both interferon (IFN)-gamma and interleukin (IL)-2 producing cells, but a dramatic increase in tumor necrosis factor (TNF)-alpha secretion in animals receiving both monoclonal antibodies. These results suggest distinct roles for CD80 and CD86 in the initiation of EAE, resulting in the diverse clinical outcomes observed in this model of EAE.

Multiple responses to administration of liposome-encapsulated hemoglobin (LEH): Effects on hematopoiesis and serum IL-6 levels

Liposome-encapsulated hemoglobin (LEH) has been tested in animals as an oxygen-carrying red cell substitute and has been shown to be beneficial in the treatment of hemorrhagic shock. The effects of LEH on immune responses have not been studied thoroughly in any well-controlled model. Using a murine model, we evaluated nephrotoxicity and hepatotoxicity as well as immune function parameters following LEH administration. Following intravenous administration of LEH, 1) a serum spike of interleukin-6 (IL-6) occurred in mice at 4-8 hours, with no elevation of IL-1, tumor necrosis factor (TNF), or interferon-gamma (IFN-gamma); 2) the serum liver function enzymes SGOT (AST, aspartate aminotransferase) and SGPT (ALT, alanine aminotransferase) were elevated at 48 hours; 3) only a slight increase in serum antibody to bovine hemoglobin was observed; and 4) increased hematopoietic activity was observed in the spleen and bone marrow. The finding that only IL-6 but not the associated TNF, IL-1, or IFN-gamma is secreted in vivo following LEH administration is novel and may have significance in defining the mechanisms underlying specific adverse responses observed with LEH administration in animals.

Nutrient-independent and nutrient-dependent factors stimulate protein synthesis in colostrum-fed newborn pigs

We hypothesized that nonnutrient components, including growth factors, present in colostrum contribute to the stimulation of protein synthesis in colostrum-fed neonatal pigs. We studied neonatal pigs fed mature milk, colostrum, or a formula containing a macronutrient composition comparable to that of colostrum for 24 h. We measured the circulating concentrations of insulin, insulin-like growth factor I, glucose, and amino acids at intervals throughout the 24-h period, after which we measured in vivo protein synthesis using a flooding dose of [3H]phenylalanine. The rates of protein synthesis in several tissues measured after 24 h of feeding were greater than those we reported previously after 6 h of feeding. The acute (within 6 h) stimulation of protein synthesis in visceral and skeletal muscle tissues of neonatal pigs fed milk, colostrum, or formula was primarily influenced by nutrient intake and associated with rapid secretion of insulin. Indirect evidence suggests that intestinal absorption of ingested colostral insulin was minimal. However, the sustained increase in tissue protein synthesis between 6 and 24 h coincided with an increase in circulating insulin-like growth factor I. We found a novel, specific stimulation of skeletal muscle and jejunal protein synthesis in colostrum-fed pigs that can be attributed to some nonnutrient component of colostrum.

Porcine brain microvascular endothelial cells support the in vitro expansion of human primitive hematopoietic bone marrow progenitor cells with a high replating potential: requirement for cell-to-cell interactions and colony-stimulating factors

Primary autologous as well as allogeneic and xenogeneic stroma will support human stem cell proliferation and differentiation for several months. In the present study, we investigated the capacity of porcine microvascular endothelial cells (PMVECs) together with combinations of cytokines (granulocyte-macrophage colony-stimulating factor [GM-CSF] + stem factor [SCF], interleukin-3 [IL-3] + SCF + IL-6, and GM-CSF + IL-3 + SCF + IL-6) to support the expansion and development of purified human CD34+ bone marrow cells. In short-term cultures (7 days), the greatest expansion of nonadherent hematopoietic cells and clonogenic progenitors was seen with CD34+ cells in direct contact with PMVEC monolayers (PMVEC contact), followed by PMVEC noncontact and liquid suspension cultures, respectively. Maximal expansion of nonadherent cells (42-fold) and total CD34+ cells (12.6-fold) occurred in PMVEC contact cultures treated with GM-CSF + IL-3 + SCF + IL-6, with similar increases in the number of granulocyte-macrophage colony-forming units (CFU-GM), CFU-mix, erythroid burst-forming units (BFU-E), CFU-blast and CFU-megakaryocyte (CFU-Mk) progenitor cells. Moreover, the number of CD34+ CD38- and CD34+ CD38+ cells increased 148.1-fold and 8.0-fold, respectively. Replating studies show that cells from day 7 dispersed blast cell colonies generated on cytokine-treated PMVEC monolayers have a high replating potential for multilineage progenitor cells. In long-term PMVEC contact cultures, CD34+ cells seeded onto PMVEC monolayers with GM-CSF + IL-3 + SCF + IL-6 showed a total calculated expansion of over 5,000,000-fold of nonadherent cells over 35 days in culture. Maximal clonogenic cell production was observed at day 28, with 6,353-fold for total CFC and comparable increases for CFU-GM, CFU-mix, CFU-blast, BFU-E, and CFU-Mk. The total number of CD34+ cells increased 2,584-fold at day 28. Furthermore, the extended growth kinetics of these cultures indicates that these phenotypically primitive progenitor cells are also functionally expanded on PMVEC monolayers. These results support the hypothesis that direct contact with a PMVEC monolayer supports the initial expansion of hematopoietic progenitor cells with a high replating potential and, possibly, a more primitive phenotype (CD34+, CD34+/CD38-).

Both maternal over- and undernutrition during gestation increase the adiposity of young adult progeny in rats

We examined the influence of maternal diet during gestation on the growth and body composition of the progeny. On day 1 of gestation, rat dams were assigned to one of four feeding regimens: free access to standard rodent chow throughout gestation (AL); 20 g feed/day (prebreeding intake) throughout gestation (PB); 10 g feed/day from day 1 to day 14, then ad libitum from day 15 to parturition (RAL); 10 g feed/day from day 1 to 14, then 20 g/day to parturition (RPB). Progeny were fed ad libitum on standard chow diet from 3 to 12 weeks of age; food intake and weight gain were measured over this time. Body composition was measured at 12 weeks. The PB regimen restricted maternal food intake during the third trimester only; the RAL regimen restricted intake by 50% for two trimesters and produced hyperphagia in the third; the RPB regimen restricted intake by 50% for two trimesters, then intake (per unit body weight) was similar to that of AL dams during the third trimester. Litter size and progeny birth, weaning, and 12-week body weights were similar among the four groups. At 12 weeks of age, PB progeny had the highest body fat (per kg fat-free mass), despite similar feed intake during the 9-week postweaning period. The increased fat was proportionally distributed among intra-abdominal and subcutaneous depots. Progeny of RAL, AL, and RPB dams had similar amounts of body fat, but in RAL progeny more fat was present in intra-abdominal depots. The weights of fat-free mass, gastrointestinal tract and hindlimb skeletal muscles were unaffected by maternal diet. Restriction of maternal feed intake during the third week of gestation had subtle effects on the body composition of young adult progeny that could not be explained on the basis of differences in postweaning voluntary feed intake.

Amino acid composition of pinniped milk

The total amino acid concentration and the amino acid pattern, i.e. the relative proportion of each amino acid (protein-bound plus free) to the total amino acids, in the milks of the Northern elephant seal, Antarctic fur seal, California sea lion, and Australian sea lion were determined. Total amino acid concentration was 10% (w/v) or greater and did not vary significantly among species. The most abundant amino acids in the milks of all species were glutamate, proline and leucine. Essential amino acids were 40%, branched-chain amino acids were 20%, and sulfur amino acids were 4% of the total milk amino acids in all species. There were differences among the pinnipeds in some of the individual amino acids; the milk of the Northern elephant seal was the most distinct among the pinnipeds with higher histidine, serine and cystine contents and a lower methionine content than that of other pinnipeds. There was little effect of stage of lactation on total amino acid concentration or amino acid pattern in pinniped milk. Comparison of milk from the four pinniped species with that of 14 other mammalian species suggests commonality in milk amino acid pattern despite the wide variation in total amino acid concentration among the species.

Amino acid composition of the milk of some mammalian species changes with stage of lactation

To determine whether the amino acid composition of milk changes during lactation, we compared the amino acid pattern (concentration of each individual amino acid relative to the total amino acid concentration) of colostrum with that of mature milk in six mammalian species. In the human, horse, pig and cow, the pattern of amino acids changed between colostrum and mature milk: glutamate, proline, methionine, isoleucine and lysine increased; cystine, glycine, serine, threonine and alanine decreased. In these four species, the total amino acid concentration also decreased 75% between colostrum and mature milk. In the baboon (Papio cynocephalus anubis and Papio cynocephalus anubis/Papio cynocephalus cynocephalus) and rhesus monkey (Macaca mulatta), however, there was little change in the pattern of amino acids between colostrum and mature milk, and total amino acid concentration decreased only about 25% between colostrum and mature milk. Mature milk rather than colostrum was the most similar among the three primates in both amino acid pattern and total amino acid concentration. We conclude, in those species in which total amino acid concentrations decline substantially between colostrum and mature milk, amino acid patterns also change. The presence of a change in amino acid pattern and total amino acid concentration during lactation appears to be unrelated to phylogenetic order.

A protein complex required for signal-sequence-specific sorting and translocation

We have purified a nascent-polypeptide-associated complex (NAC) which prevents short ribosome-associated nascent polypeptides from inappropriate interactions with proteins in the cytosol. NAC binds nascent-polypeptide domains emerging from ribosomes unless a signal peptide is fully exposed. Depletion of cytosolic proteins (including NAC) from ribosomes carrying nascent polypeptides allows the signal recognition particle (SRP) to crosslink to polypeptides irrespective of whether or not they contain signal peptides. In the absence of cytosol, proteins lacking signal peptides can be mistranslocated into the endoplasmic reticulum in vitro, albeit with low efficiency. Readdition of NAC restores the specificity of SRP and fidelity of translocation.

Amino acid composition of human milk is not unique

To determine whether the amino acid pattern of human milk is unique, we compared the amino acid pattern of human milk with the amino acid patterns of the milks of great apes (chimpanzee and gorilla), lower primates (baboon and rhesus monkey) and nonprimates (cow, goat, sheep, llama, pig, horse, elephant, cat and rat). Amino acid pattern was defined as the relative proportion of each amino acid (protein-bound plus free) (in mg) to the total amino acids (in g). Total amino acid concentration was lower in primate milk than in nonprimate milk. There were commonalities in the overall amino acid pattern of the milks of all species sampled; the most abundant amino acids were glutamate (plus glutamine, 20%), proline (10%) and leucine (10%). Essential amino acids were 40%, branched-chain amino acids 20%, and sulfur amino acids 4% of the total amino acids. The amino acid pattern of human milk was more similar to those of great apes than to those of lower primates. For example, cystine was higher and methionine was lower in primate milks than in nonprimate milks, and in great ape and human milks than in lower primate milks. Because the milk amino acid patterns of the human and elephant, both slow-growing species, were dissimilar, the amino acid pattern of human milk seems unrelated to growth rate.

Leucine oxidation changes rapidly after dietary protein intake is altered in adult women but lysine flux is unchanged as is lysine incorporation into VLDL-apolipoprotein B-100

We measured the 13C enrichments of expired CO2 and deuterium enrichments of plasma free lysine and VLDL-apolipoprotein B-100 in five nulliparous women who received an oral bolus dose of [1-13C]leucine and a primed, constant infusion of [2H4]lysine on d 2 and 6 while consuming protein diets of 1.5, 1.0 and 0.4 g.kg-1 x d-1. Peak enrichments and cumulative percent recoveries of 13C in expired CO2 increased during the high, and decreased during the low protein periods within 24 h of altered intakes; these changes averaged 89% of that on d 6 of the high and low protein diets. The early changes in leucine oxidation showed significant relationships with urinary nitrogen excretion on d 6 of the dietary periods. The ratio of the isotopic enrichment of lysine in VLDL-apolipoprotein B-100 to that in plasma was unaltered by the level of protein intake. Thus, amino acid oxidation adapts rapidly to altered protein intakes in adult women and is useful to determine protein needs during rapidly changing physiologic conditions. However, 6-d periods of protein intake over the range of 1.5 to 0.4 g.kg-1 x d-1 do not affect the proportional use of dietary amino acids for hepatic secretory protein synthesis.

Control of folding and membrane translocation by binding of the chaperone DnaJ to nascent polypeptides

Recent evidence supports the view that cellular protein folding may be mediated by molecular chaperones. A fundamental question concerns the stage in its biogenesis at which the folding protein makes first contact with these components. We show here by crosslinking that the chaperone DnaJ binds nascent ribosome-bound polypeptide chains as short as 55 residues. Cotranslational binding of DnaJ to firefly luciferase and chloramphenicol acetyltransferase resulted in an arrest of folding as long as the functional partners of DnaJ in Escherichia coli, DnaK and GrpE, were missing. Protein uptake into microsomes and mitochondria was also interrupted by DnaJ. Both folding and post-translational translocation recommenced upon addition of DnaK and GrpE. We propose that DnaJ protects nascent polypeptide chains against aggregation and, in cooperation with Hsp70, controls their productive folding once a complete polypeptide or a polypeptide domain has been synthesized.

Enhanced response of muscle protein synthesis and plasma insulin to food intake in suckled rats

To compare the sensitivity of muscle protein synthesis to food intake in neonatal and weaned rats, 5- and 16-day-old suckled rats and 28-day-old weaned rats were either fed, fasted for 8-10 h, or refed for 1-4 h after an 8-h fast. Protein synthesis was measured in vivo in soleus and plantaris muscles with a large dose of L-[4-3H]phenylalanine. In fed rats, fractional rates of protein synthesis (KS) decreased with age. Fasting decreased KS, and refeeding increased KS most in 5-day-old animals, less in 16-day-old rats, and least in 28-day-old rats. In 5-day-old rats, there were no differences in KS between soleus and plantaris muscles in the fed state and after fasting and refeeding; at 28 days, KS was higher in soleus than in plantaris in fed rats, and the soleus did not respond to fasting and refeeding. In rats at all three ages, the concentration of most plasma amino acids decreased during fasting; when 5-day-old rats were refed, plasma amino acid concentrations increased, but not to the levels in the fed state. Plasma insulin concentrations increased with age. Plasma insulin concentrations decreased more rapidly with fasting and increased more extensively with refeeding in 5-day-old rats than in older rats. These results suggest that muscle protein synthesis is more responsive to food intake in young suckled rats than in older suckled or weaned rats; this increased responsiveness is accompanied by greater changes in circulating insulin concentrations.

Amino acid compositions of body and milk protein change during the suckling period in rats

The amino acid concentrations of rat body protein and rat milk protein were measured at 1, 6, 10 and 16 d of age to determine whether the concentration of each amino acid in proportion to the concentration of total recovered amino acids (amino acid composition) in the body changes during early growth and development and whether parallel changes occur in the amino acid composition of milk. The ratio of essential to nonessential amino acids in bodies decreased 10% during the suckling period (P < 0.05). The ratio of essential to nonessential amino acids in milk proteins decreased by 6% (P < 0.05). With the exception of threonine, the body to milk ratio for each essential amino acid seemed similar to that for the other essential amino acids, implying that most essential amino acids are equally limiting for the synthesis of body protein in exclusively milk-fed pups. Measurements of milk intake and milk composition were used to determine amino acid intakes and hence the efficiency with which milk amino acids were used for body protein deposition. The efficiency of essential amino acid utilization was 75% between 1 and 6 d, 86% between 6 and 10 d, and 62% between 10 and 16 d of age. Although the overall efficiency of nonessential amino acid utilization showed a similar pattern, the results suggested the need for a high degree of glycine and arginine synthesis.