Peptides corresponding to CD4-interacting regions of murine MHC class II molecules modulate immune responses of CD4+ T lymphocytes in vitro and in vivo

Immune responses mediated by CD4+ T cells depend on Ag-specific alpha beta TCRs that recognize the specific antigenic peptide presented by MHC class II molecules. Interactions between CD4 coreceptors and monomorphic regions of MHC class II molecules contribute to these responses. To examine whether immune reactions could be modulated by specifically interfering with CD4-MHC class II interactions, we have used, in various in vitro and in vivo assays, peptides that correspond to a region of MHC class II molecules previously shown to control interaction with CD4. Depending on the chemical nature and concentration of these peptides, they modulated Ag-specific responses of CD4+ T cells. At high concentrations, these peptides inhibited T cell responses in vitro. However, under conditions that can cause Ag-induced unresponsiveness, the peptides enhanced T cell responses. Also, primary in vivo immune responses to systemically administered soluble protein Ag, keyhole limpet hemocyanin, were enhanced when mice were treated with peptides corresponding to the CD4-interacting region of MHC class II molecules but not when treated with control peptides. Lymphokine profiles suggested that the peptides may favor the differentiation of Th1 cells, because lymphocytes from peptide-treated mice secreted more IL-2 and IFN-gamma than lymphocytes from nontreated or control-peptide-treated mice upon restimulation with Ag in vitro. These results demonstrate that MHC class II-derived peptides can directly interfere with interactions with CD4 and modulate T cell responses in vitro and in vivo.

Peptides corresponding to CD4-interacting regions of murine MHC class II molecules modulate immune responses of CD4+ T lymphocytes in vitro and in vivo

Immune responses mediated by CD4+ T cells depend on Ag-specific alpha beta TCRs that recognize the specific antigenic peptide presented by MHC class II molecules. Interactions between CD4 coreceptors and monomorphic regions of MHC class II molecules contribute to these responses. To examine whether immune reactions could be modulated by specifically interfering with CD4-MHC class II interactions, we have used, in various in vitro and in vivo assays, peptides that correspond to a region of MHC class II molecules previously shown to control interaction with CD4. Depending on the chemical nature and concentration of these peptides, they modulated Ag-specific responses of CD4+ T cells. At high concentrations, these peptides inhibited T cell responses in vitro. However, under conditions that can cause Ag-induced unresponsiveness, the peptides enhanced T cell responses. Also, primary in vivo immune responses to systemically administered soluble protein Ag, keyhole limpet hemocyanin, were enhanced when mice were treated with peptides corresponding to the CD4-interacting region of MHC class II molecules but not when treated with control peptides. Lymphokine profiles suggested that the peptides may favor the differentiation of Th1 cells, because lymphocytes from peptide-treated mice secreted more IL-2 and IFN-gamma than lymphocytes from nontreated or control-peptide-treated mice upon restimulation with Ag in vitro. These results demonstrate that MHC class II-derived peptides can directly interfere with interactions with CD4 and modulate T cell responses in vitro and in vivo.

The regulation by gender, strain, dose, and feeding status of the induction of multiple forms of cytochrome P450 isozymes in rat hepatic microsomes by 2,4,5,2',4',5'-hexachlorobiphenyl

2,4,5,2',4',5'-hexachlorobiphenyl (HCB) induces hepatic microsomal cytochromes P450 with a similar selectivity for responsive genes to phenobarbital (PB). CYP2Bl, CYP2B2, CYP2C6, CYP3Al, and CYP2Al each showed large strain differences in induction by HCB Fisher F344 >> Wistar Furth (WF) that were much more evident in female rats, paralleling previous observations with PB. These five P450s and epoxide hydrolase were, however, induced more effectively by HCB than by PB and strain differences were even larger. With HCB, strain differences in male rats were much more apparent than with PB. This change was not due to the greater HCB induction since a 2-fold lower induction was maintained even with a 10-fold lower dose of HCB. The sex and strain differences were seen both by immunoblot analysis and by form-selective enzyme activity assays. induction of CYP2B1, CYP2B2, and CYP3A1 by HCB was decreased 3-fold when starvation during the final 24 hr was replaced by continuous feeding. This effect was similar in each strain and therefore independent of the regulatory processes associated with the differential suppression of induction in WF rats. This modulation of induction by feeding was also seen with PB which caused only a 30% lowering of induction in continuously fed F344 rats. A 52-kDa microsomal protein (p52) was prominently induced by both HCB and PB after starvation, while minor induction of a 50-kDa microsomal protein (p50) also occurred after the same treatment. Furthermore, a 100-kDa microsomal protein (p100) was induced by HCB but not by PB and only in rats that were continuously fed. These results suggest that the induction of multiple forms of P450 following HCB treatment functions through the same PB-stimulated pathway that shows a strain-dependent endocrine (GH/T3/testosterone)-sensitive suppression mechanism. The induction of p5O, p52, and plOO by HCB suggests the presence of at least two additional hepatic response mechanisms for HCB.

Is the CvaA protein, encoded within the colicin V export gene cvaA, required for colicin V transport?

The antibacterial peptide toxin colicin V is exported from Escherichia coli cells by a signal sequence-independent, ABC export system. Export requires at least three proteins-membrane fusion protein CvaA, ABC export protein CvaB, and outer membrane protein TolC. The cvaA gene also encodes a second protein, CvaA, initiated from an in-frame translational re-start within the cvaA coding sequence. To determine whether the internally encoded CvaA protein also functions in the export pathway, the putative start codons for CvaA were mutagenized, while maintaining CvaA function. Elimination of CvaA translation caused no change in colicin V export levels, indicating that the CvaA protein is not required in the secretion pathway.

Acute bacterial meningitis in children in Hefei, China 1990-1992

OBJECTIVE

To obtain etiologic and epidemiologic information about bacterial meningitis, especially the H influenza type B (Hib), from a medium-sized city, Hefei, China.

METHODS

Data were collected prospectively over 3 years, from 1990 to 1992 by a well-organized group including 13 hospitals. All children with a clinical diagnosis of acute bacterial meningitis were enrolled and the specimens were taken for the etiologic studies. CSF and blood were tested by standard bacteriologic technique. CSF, blood and concentrated urine were tested directly for detection of antigen by countercurrent immuno-electrophoresis (CIE). Data were analyzed by epidemiologic methods.

RESULTS

Bacterial culture and CSF Gram's staining were positive only in 13.3% and 11.7%, respectively. Bacterial antigen detection was positive in up to 90% by CIE which was more sensitive than bacterial culture (chi 2 = 67.7, P < 0.005). The annual incidence of acute bacterial meningitis in the city is calculated as 9.3 cases/100,000 children from 1 month to 15 years of age and 19.2 cases/100,000 children from 1 month to 5 years of age. Hib meningitis accounted for 51.7%, N. meningitis (Nm) for 38.3%, and S. pneumoniae (Sp) for 8.3%. There was no significant seasonal variation. Of the patients, 76.7% were children under 5 years of age, and 51.7% under 1 year of age. The case fatality rate was 11.7% for all bacterial meningitis, 9.7% for Hib, 17.4% for Nm and 20% for Sp. A total of 22.6% of survivors suffered from neurological or psychological problems.

CONCLUSIONS

Using antigen detection combined with bacterial culture, we could make an etiologic diagnosis in up to 90% of the patients in this group. Hib, Nm and Sp were the predominant pathogens, which was similar to the findings in other countries. Hib was the most common cause of bacterial meningitis, but the incidence was much lower than in most parts of the world.

Childhood lead poisoning in China

In China, comprehensive epidemiological data relating to the prevalence of childhood lead poisoning are not available. However, existing data suggest that this disease may be widely pervasive as a result of rapid industrialization and the use of leaded gasoline. Seventeen publications have reported elevated blood lead levels in children from different areas of the country. Children residing in industrial and busy traffic areas had average blood lead levels(BPb) of 21.8-67.9 mu g/dl. The percentages of BPb values above 10 mu g/dl, which is the definition of lead poisoning in children, ranged from 64.9% to 99.5%. Even for 'unexposed' children, about 50% of them had BPb values above 10 mu g/dl. Furthermore, several retrospective pilot studies were conducted in Shanghai, Shenyang, Fuzhou and Beijing to evaluate the health effects of lead at current degree of exposure. The link between low-level lead exposure and deficits in IQ, neurobehavioral development and physical growth is remarkably consistent without exception. In summary, the harmful health effects of childhood lead poisoning in limited studies of exposed and 'unexposed' children demonstrate that this totally preventable disease warrants considerable public health attention in China.

[Relationship between lead content in umbilical blood and neurobehavioral development in infants]

One hundred and thirty-two babies were selected and their umbilical blood lead level were determined as a marker to reflect their exposure, to study the diagnostic criteria for lead poisoning in young children. And, mental development index (MDI) and psychomotor development index (PDI) of three-month babies in Bayley scales of infant development were used as effective indicators to study levels of lead on their development. Results indicated that both MDI and PDI in infants with blood lead levels of greater than or equal to 0.48 mumol/L were obviously lower than those with less than 0.48 mumol/L. All children were divided into two groups (high-blood-lead and low-blood-lead) according to the cut-off values for blood lead of 0.72, 0.48, and 0.24 mumol/L, respectively, and the difference in MDI and PDI between the two groups decreased gradually with the cut-off value shifted down, and there was no difference in them between the two groups when the cut-off point lowering down to 0.24 mumol/L. Therefore, the authors recommended that a level of 0.48 mumol/L of blood lead be used as diagnostic criteria for lead poisoning in young children.

[Metabolism and utilization of calcium derived from hydrolysed oyster shell in rats]

Experimental rats modeled on calcium deficiency were fed with calcium derived from hydrolysed oyster shell, calcium carbonate and calcium chloride respectively, equivalent to 45 mg a day, for four weeks to study their bioavailability. Calcium contents in the blood, urine, feces and bone of rats were determined with atomic absorption spectrometry and EDTA complex titration, and their bone density was measured with densitometry. Results showed proportions of calcium absorption and retention were 67.3% +/- 16.7% and 64.6% +/- 17.5%, respectively, in rats fed with calcium from hydrolysed oyster, and their femur calcium content and bone density (BMC/BW) 131.2 +/- 1.48 mg/g and 0.318 +/- 0.034 g/cm2, respectively, significantly higher than those in the rats fed with calcium carbonate. There were no significant difference in blood calcium contents, weight gains and feed intake between those three groups of rats. It suggests that calcium derived from hydrolysed oyster shell may be absorbed and utilized more easily than calcium carbonate.

Cytochromes CYP1A1 and CYP1B1 in the rat mammary gland: cell-specific expression and regulation by polycyclic aromatic hydrocarbons and hormones

Cultured rat mammary cells express both CYP1A1 and CYP1B1 in response to polycyclic aromatic hydrocarbons (PAH) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in a cell type-specific manner. The expression of each P450 was determined functionally (regioselective PAH metabolism), as apoprotein (immunoblots) and as mRNA (Northern hybridization). The epithelial rat mammary cells (RMEC) expressed CYP1A1, however only after PAH or TCDD treatment. CYP1B1 protein was scarcely detected in these induced RMEC but was surprisingly active as a participant in 7,12-dimethylbenz[a]anthracene (DMBA) metabolism shown through selective antibody inhibition (40% of total activity). CYP1B1 was selectively expressed in the stromal fibroblast population of rat mammary cells to the exclusion of CYP1A1. In the rat mammary fibroblasts (RMF), CYP1B1 protein and associated activity were each present at low levels constitutively and were highly induced by benz[a]anthracene (BA) to a greater extent than by TCDD (12- versus 6-fold). However, BA (10 microM) and TCDD (10 nM) stimulated the 5.2-kb CYP1B1-specific mRNA equally. These increases are consistent with the involvement of the aryl hydrocarbon (Ah) receptor in the transcription of the CYP1B1 gene and with the additional stabilization of CYP1B1 protein by BA, previously observed in embryo fibroblasts. Exactly this regulation of CYP1B1-dependent activity was seen in RMEC suggesting that this arises from exceptionally active CYP1B1 in a small proportion (5%) of residual RMF. The constitutive expression and PAH inducibility of CYP1B1 and CYP1A1 proteins in RMF and RMEC, respectively, were each substantially decreased (approximately 75%) by a hormonal mixture (17 beta-estradiol (0.2 microM) progesterone (1.5 microM) cortisol (1.5 microM) and prolactin (5 micrograms/ml)). Progesterone and cortisol, added singly to RMF suppressed CYP1B1 protein expression (approximately 80%) in both untreated and BA-induced cells, while cortisol also suppressed the 5.2-kb CYP1B1 mRNA. In contrast, 17 beta-estradiol stimulated constitutive expression of CYP1B1 protein (50-75%) and mRNA level (2- to 3-fold), but did not affect CYP1B1 expression in BA-treated RMF. The expression of CYP1A1 and CYP1B1 is therefore highly cell specific even though each is regulated through the Ah receptor. Each P450 exhibits a surprisingly similar pattern of hormonal regulation even though expressed in different cell types.

Topology analysis of the colicin V export protein CvaA in Escherichia coli

The antibacterial protein toxin colicin V is secreted from Escherichia coli cells by a dedicated export system that is a member of the multicomponent ATP-binding cassette (ABC) transporter family. At least three proteins, CvaA, CvaB, and TolC, are required for secretion via this signal sequence-independent pathway. In this study, the subcellular location and transmembrane organization of membrane fusion protein CvaA were investigated. First, a series of CvaA-alkaline phosphatase (AP) protein fusions was constructed. Inner and outer membrane fractionations of cells bearing these fusions indicated that CvaA is inner membrane associated. To localize the fusion junctions, the relative activities of the fusion proteins, i.e., the amounts of phosphatase activity normalized to the rate of synthesis of each protein, as well as the stability of each fusion, were determined. These results indicated that all of the fusion junctions occur on the same side of the inner membrane. In addition, the relative activities were compared with that of native AP, and the protease accessibility of the AP moieties in spheroplasts and whole cells was analyzed. The results of these experiments suggested that the fusion junctions occur within periplasmic regions of CvA. We conclude that CvaA is an inner membrane protein with a single transmembrane domain near its N terminus; the large C-terminal region extends into the periplasm. This study demonstrates the application of AP fusion analysis to elucidate the topology of a membrane-associated protein having only a single transmembrane domain.

Maximal airway response in mature and immature rabbits during tidal ventilation

Airway closure during maximal methacholine (MCh) challenge was evaluated using alveolar capsules in eight immature and eight mature anesthetized rabbits in vivo during imposed tidal ventilation. Changes in airway opening and alveolar pressures (delta PA) and pulmonary resistance (RL) were measured during MCh challenge at a positive end-expiratory pressure of 5 cmH2O. In immature rabbits, delta PA remained > 3 cmH2O in all animals, indicating no detectable airway closure. This contrasts to our previous study of isolated immature rabbit lungs under static conditions in which delta PA was < 0.1 cmH2O during maximal MCh challenge, findings consistent with airway closure. Airway closure also did not occur in mature animals during tidal ventilation in vivo; however, the frequency of closure in isolated lungs under static conditions was very low. With increasing MCh, end-expiratory PA increased in immature but not in mature rabbits. RL did not reach a plateau in immature rabbits during MCh, whereas a plateau was reached in mature rabbits. Immature rabbits also had greater increases in RL. These results suggest that tidal ventilation can limit bronchoconstriction in immature rabbits and prevent airway closure during maximal MCh challenge. Tidal ventilation may limit bronchoconstriction by inhibitory effects of stretch on airway smooth muscle contraction and also by causing hyperinflation and thereby increasing transpulmonary pressure.

Involvement of both major histocompatibility complex class II alpha and beta chains in CD4 function indicates a role for ordered oligomerization in T cell activation

CD4 is a membrane glycoprotein on T lymphocytes that binds to the same peptide:major histocompatibility complex (MHC) class II molecule recognized by the antigen-specific receptor (TCR), thereby stabilizing interactions between the TCR and peptide;MHC class II complexes and promoting the localization of the src family tyrosine kinase p56lck into the receptor complex. Previous studies identified a solvent-exposed loop on the class II beta 2 domain necessary for binding to CD4 and for eliciting CD4 coreceptor activity. Here, we demonstrate that a second surface-exposed segment of class II is also critical for CD4 function. This site is in the alpha 2 domain, positioned in single class II heterodimers in such a way that it cannot simultaneously interact with the same CD4 molecule as the beta 2 site. The ability of mutations at either site to diminish CD4 function therefore indicates that specifically organized CD4 and/or MHC class II oligomers play a critical role in coreceptor-dependent T cell activation.

Linker histones are not essential and affect chromatin condensation in vivo

We have (separately) disrupted all of the expressed macronuclear copies of the HHO gene encoding macronuclear histone H1 and of the micronuclear linker histone (MLH) gene encoding the protein MicLH in Tetrahymena thermophila. These disruptions are shown to eliminate completely the expression of each protein. Strains without either linker histone grow at normal rates and reach near-normal cell densities, demonstrating that linker histones are not essential for cell survival. Histone H1 knockout (delta H1) cells have enlarged DAPI-stained macronuclei and normal-sized micronuclei, while MicLH knockout (delta MicLH) cells have enlarged micronuclei and normal-sized macronuclei. delta MicLH cells undergo mitosis normally. However, the micronuclear mitotic chromosome structure is less condensed. These studies provide evidence that linker histones are nonessential and are involved in chromatin packaging and condensation in vivo.

[Experimental studies of protective effects of ischemic myocardium preconditioning and its mechanism]

Recent research has shown that repeated brief myocardial ischemia (RBMI) can increase the tolerance of myocardium to a subsequent sustained ischemia and have protective effects on myocardial cells. With the isolated rat heart Langendorff model, we investigated the effects of RBMI on myocardial morphology, systolic function, coronary flow rates (CFR), myocardial membrane phospholipid (PL) content and its marker enzyme's activity (5'-AMPase). The results showed: After ischemia-reflow, the HR, LVP and CFR in control and experimental groups had no significant difference (P > 0.05). But the PL content and specific activity of 5'-AMPase were significantly higher in the experimental group than that in control group (P < 0.01, P < 0.05). And the observations of ultrastructure suggested that the myocardium of the experimental group was preserved better than that in control group. It was also shown that RBMI had protective effects on myocardial membrane structure, and however effective had no relation to CFR.

Effect of transpulmonary pressure on airway closure in immature and mature rabbits

The transpulmonary pressures (Ptp values) at which airway closure occurred during maximal stimulation with methacholine were compared in 10 mature and 9 immature rabbit lungs by using an alveolar capsule technique to assess airway closure. After maximal constriction, airway opening and alveolar capsule pressures were recorded during small volume oscillations as Ptp was lowered from 12 to 4 cmH2O. At each Ptp, the proportion of alveolar capsules indicating airway closure was greater for the immature than for the mature lungs (P < 0.025). At Ptp of 4 cmH2O, only 20% of alveolar capsules indicated airway closure in the mature lungs in contrast to 85% indicating closure in the immature lungs (P < 0.001). The in vitro sensitivity of tracheal smooth muscle to acetylcholine and histamine was greater in tissues from immature than from mature rabbits. We conclude that the more frequent airway closure observed in immature rabbits could reflect maturational differences in the structure of the bronchi or lung parenchyma or differences in the coupling between the parenchyma and the airways.

[Effects of lyophilized royal jelly on experimental hyperlipidemia and thrombosis]

Rat models with experimental hyperlipidemia were fed with lyophilized royal jelly 700 mg/kg body weight daily for six weeks. Results showed lyophilized royal jelly can reduce serum cholesterol level (P < 0.01) and increase high-density lipoprotein-cholesterol level (P < 0.05). Lyophilized royal jelly can also increase the red cell deformability (RCD) and decrease plasma fibrinogen level. Thrombus was formed less in trial animals than in controls with a statistical significance. It suggested lyophilized royal jelly can be used in preventing and treatment of hyperlipidemia, and improving highly-coagulant status of blood.

Activation of neutrophils by a chemically separated but optically coupled neutrophil population undergoing respiratory burst

Neutrophils from pig blood were used as a model system to investigate the optical communication between cells. It was found that neutrophils stimulated to undergo respiratory burst can activate a second, chemically separated, but optically coupled population of neutrophils. The response of the latter was visualized as a temporary rising of their low-level chemiluminescence and an enhanced generation of superoxide radicals detected by both the reduction of ferricytochrome c and spin trapping. The results provide evidence that a long-range optical coupling of biological significance between living cells exists.

Alteration of lysophosphatidylcholine content in low density lipoprotein after oxidative modification: relationship to endothelium dependent relaxation

OBJECTIVE

The aim was to examine the formation of lipid peroxidation products and the alteration in phospholipid content in low density lipoprotein (LDL) after oxidative modification by CuSO4, and subsequently, to determine the ability of the modified LDL to impair endothelium dependent relaxation in rat aortic rings.

METHODS

Blood samples were obtained from normal human volunteers. LDL was prepared by sequential ultracentrifugation and it was oxidatively modified in the presence of 5 microM CuSO4. Lipid peroxidation products (thiobarbituric acid reactive substances, TBARS), and alterations in electrophoretic mobility and phospholipid content were determined in normal (native) and oxidised LDL. Endothelium dependent relaxation was produced by acetylcholine (10(-8)-10(-5) M) in phenylephrine precontracted rat aortic rings.

RESULTS

LDL incubated for 24 h with 5 microM CuSO4 at 20 degrees C and 37 degrees C with constant agitation displayed higher amounts of TBARS than the respective native LDL. While the amounts of TBARS in LDL modified at 20 degrees C and 37 degrees C were similar, the former condition resulted in statistically smaller changes of phospholipid contents. LDL with higher lysophosphatidylcholine content showed greater impairment of endothelium dependent relaxation in rat aortic rings than LDL with lower lysophosphatidylcholine content.

CONCLUSIONS

The raised lysophosphatidylcholine level in oxidatively modified LDL was related to the ability of the LDL to impair endothelium dependent relaxation. However, lipid peroxidation products assessed by TBARS did not relate to the phospholipid changes in LDL and therefore cannot be used to predict the vascular effects of LDL after oxidative modification.

[Effect of nifedipine on T wave in ischemic myocardium]

Calcium antagonists are generally considered to have no substantial effect on repolarization of the myocardium, so they have no direct effect on T wave, either. But in a pig model of myocardial ischemia, intracoronary nifedipine was found to reverse the inverted T wave induced by ischemia to upright promptly. Ten pigs were anesthetized with the chest opened, anterior interrentricular branch of left coronary artery (LAD) was narrowed to 4.67 kPa of LAD pressure, and then adenosine or nifedipine was infused into the coronary respectively. During the 9-minute ischemia, intracoronary adenosine or intracoronary nifedipine got the similar HR, LVEDP, LVDP, CAP, CAQ, and the intracoronary adenosine even got higher CAQ than the intracoronary nifedipine did. However, the T wave was retained inverted during the adenosine infused, but during the intracoronary nifedipine, the inverted T wave was promptly turned upright. The relevant factors and mechanisms are discussed.

[Effects of endotoxin on coronary circulation]

To investigate the effects of endotoxin (ETX) on coronary circulation, we infused endotoxin (4ng/ml) intravenously in a small dose (0.3ng/kg.min-1) which did not reduce the blood pressure, nor did it disturb the coronary autoregulation, and the flow kept constant during the ETX infusion. But when the left coronary artery descending branch (LAD) was narrowed and the LAD pressure was reduced to 4.67kPa, the ETX showed a vasodilator effect on the LAD (pre-ETX 65.2 +/- 29.2 ml/min, post-ETX 89.5 +/- 32.7 ml/min, P < 0.05). This effect suggested that the ETX in a small dose had a vasodilator effect on a narrowed coronary artery, even when it did not disturb the hemodynamics. The possible mechanisms were surveyed preliminarily.

[Comparative study of ischemia-induced and reperfusion-induced ventricular fibrillation in pigs]

To have a better understanding of reperfusion-induced ventricular fibrillation (VF), we studied the relevant morbidity in pigs and compared it with that of the ischemia-induced VF. In 10 hearts of anesthetized chest-open pigs, a total of 127 cycles of various degrees and varied duration of ischemia and reperfusion were completed. VF occurred 13 times (10.2%). Of these, 11 were ischemia-induced VF, while only 2 were reperfusion-induced VF. In two cases of ischemia-induced VF, electric defibrillation failed before the reestablishment of left anterior interventricular branch of coronary artery flow, but after adequate reflowing, all VF turned out to be sinus-rhythm by electric defibrillation. The results suggest that ventricular fibrillation be mainly induced by ischemia but less induced by reperfusion.