The functional relevance of NK-cell-mediated upregulation of antigen-specific IgG2a responses

We have previously shown that activation of NK cells by poly(I:C) or tumor treatment of mice increases the level of antigen-specific IgG2a (1, 2). We have now assessed the functional relevance of this effect of the innate immune system on the specific immune response. We found that the increased IgG2a significantly augments antibody-dependent cellular cytotoxicity mediated by NK cells both in vivo and in vitro. Furthermore, we show that both IgG3 producing plasma cells induced by T-independent antigens and IgG2a plasma cells induced in the presence of activated NK cells may be just as long-lived as plasma cells induced by T-dependent antigens. These results indicate that if NK cells are activated early in the immune response, before T cells are recruited, they could exert long-lasting effects.

Mutagenicity of methyl tertiary butyl ether

Methyl tertiary butyl ether (MTBE), the main component of oxygenated gasoline, is added to gasoline as an octane enhancer to reduce automotive emissions. We evaluated the mutagenicity of domestic MTBE using the Ames test, unscheduled DNA synthesis (UDS) assay, and NIH/3T3 cell micronucleus test. MTBE did not show any mutagenic potential in the Ames assay (TA98, TA100 strains) with or without rat liver-derived metabolic activation system (S-9). In rat primary hepatocyte UDS assay, a dose-response relationship was observed, which meant that MTBE might damage normal DNA and induce unscheduled DNA synthesis. MTBE did not show positive results in the NIH/3T3 cell micronucleus test. It could be concluded that MTBE has some degree of mutagenicity.

Effect of leaded and unleaded gasoline on the mutagenicity of vehicle exhaust particulate matter

With the removal of lead from gasoline and the use of new technologies, there have been some changes in vehicle emissions. In order to find out if the unleaded gasoline has the ability to reduce the emission of pollutants, leaded and unleaded gasoline were tested on a Santana engine dynamometer under a standard test cycle. The concentrations of hydrocarbons (HC) and carbon monoxide (CO) in emission were analyzed. The extracts of total exhaust particles were also collected and the components were detected by gas chromatography/mass spectrometry (GC/MS). A series of different end point genotoxicity tests, including the Ames test, the single cell gel electrophoresis (SCGE) assay, and micronucleus induction assay, were performed to investigate the mutagenicity in the two kinds of gasoline. We found that unleaded gasoline could reduce the emission of CO and HC and significantly decrease the quantity of vehicle exhaust particulate matter by 60%. As for the component analysis, only 23 kinds of organic substances adsorbed onto the particles were identified in the unleaded gasoline, while 32 kinds of compounds were detected in the leaded gasoline. The genotoxicity tests indicated that both types of gasoline could enhance the number of histidine-independent colonies in the Ames test, cause DNA damage, and increase the frequency of induced micronucleus in the Chinese hamster lung (CHL) cells. For the same particle weight, no difference was found between their mutagenicity. Because of the decrease in the emission of CO, HC, and particles in unleaded gasoline, this gasoline has some benefits for the environment and human health.

[Improved endocardial border delineation during dobutamine stress echocardiography using the left heart contrast medium BY 963]

The interpretation of induced wall motion abnormalities during dobutamine stress echocardiography is affected in the case of impaired image quality. In 48 consecutive patients (mean age 62 +/- 9 years, 32 males, 16 females) with suspected coronary disease undergoing coronary angiography, the transpulmonary contrast agent BY 963 was given i.v. as bolus during dobutamine stress echocardiography (10-40 micrograms kg min, plus max. 1 mg atropine) to analyze improvements in endocardial border delineation. For each of the 16 segments of the left ventricle, the endocardial border delineation was evaluated. Using BY 963 the average number of non-evaluable segments decreased by 58% from 5.2% to 2.2% at rest (p = 0.008) and by 56% from 5.9% to 2.6% at maximal stress (p = 0.003) as compared to the non-contrast study for all patients. In patients with impaired image quality, defined as at least 1 non-evaluable segment at rest without contrast enhancement (N = 14), the number of non-evaluable segments decreased from 19.2% to 8.2% (p = 0.004) at rest and from 19.2% to 9.6% (p = 0.006) at maximal stress. The greatest decrease of non-evaluable segments was seen in the lateral and anterior segments of the apical views (maximum of 80%). The improved endocardial border delineation resulted in an improved agreement between two observers in the interpretation of the dobutamine stress echocardiograms as positive or negative (kappa = 0.38 without contrast, kappa = 0.58 with contrast). Contrast application resulted in a slight improvement of diagnostic accuracy of dobutamine stress echocardiography in the detection of angiographically proven significant coronary artery disease.

CONCLUSION

In patients with impaired endocardial border delineation the use of the echo contrast agent BY 963 reduces the number of non-evaluable segments. Improvement of endocardial delineation is greatest for lateral and anterior segments in the apical views.

Characterization of a plasma membrane calcium oscillator in rat pituitary somatotrophs

In excitable cells, oscillations in intracellular free calcium concentrations ([Ca(2+)](i)) can arise from action-potential-driven Ca(2+) influx, and such signals can have either a localized or global form, depending on the coupling of voltage-gated Ca(2+) influx to intracellular Ca(2+) release pathway. Here we show that rat pituitary somatotrophs generate spontaneous [Ca(2+)](i) oscillations, which rise from fluctuations in the influx of external Ca(2+) and propagate within the cytoplasm and nucleus. The addition of caffeine and ryanodine, modulators of ryanodine-receptor channels, and the depletion of intracellular Ca(2+) stores by thapsigargin and ionomycin did not affect the global nature of spontaneous [Ca(2+)](i) signals. Bay K 8644, an L-type Ca(2+) channel agonist, initiated [Ca(2+)](i) signaling in quiescent cells, increased the amplitude of [Ca(2+)](i) spikes in spontaneously active cells, and stimulated growth hormone secretion in perifused pituitary cells. Nifedipine, a blocker of L-type Ca(2+) channels, decreased the amplitude of spikes and basal growth hormone secretion, whereas Ni(2+), a blocker of T-type Ca(2+) channels, abolished spontaneous [Ca(2+)](i) oscillations. Spiking was also abolished by the removal of extracellular Na(+) and by the addition of 10 mM Ca(2+), Mg(2+), or Sr(2+), the blockers of cyclic nucleotide-gated channels. Reverse transcriptase-polymerase chain reaction and Southern blot analyses indicated the expression of mRNAs for these channels in mixed pituitary cells and purified somatotrophs. Growth hormone-releasing hormone, an agonist that stimulated cAMP and cGMP productions in a dose-dependent manner, initiated spiking in quiescent cells and increased the frequency of spiking in spontaneously active cells. These results indicate that in somatotrophs a cyclic nucleotide-controlled plasma membrane Ca(2+) oscillator is capable of generating global Ca(2+) signals spontaneously and in response to agonist stimulation. The Ca(2+)-signaling activity of this oscillator is dependent on voltage-gated Ca(2+) influx but not on Ca(2+) release from intracellular stores.

Expression of Ca(2+)-mobilizing endothelin(A) receptors and their role in the control of Ca(2+) influx and growth hormone secretion in pituitary somatotrophs

The expression and coupling of endothelin (ET) receptors were studied in rat pituitary somatotrophs. These cells exhibited periods of spontaneous action potential firing that generated high-amplitude fluctuations in cytosolic calcium concentration ([Ca(2+)](i)). The message and the specific binding sites for ET(A), but not ET(B), receptors were found in mixed pituitary cells and in highly purified somatotrophs. The activation of these receptors by ET-1 led to an increase in inositol 1,4,5-trisphosphate production and the associated rise in [Ca(2+)](i) and growth hormone (GH) secretion. The Ca(2+)-mobilizing action of ET-1 lasted for 2-3 min and was followed by an inhibition of action potential-driven Ca(2+) influx and GH secretion to below the basal levels. As in somatostatin-treated cells, the ET-1-induced inhibition of spontaneous electrical activity and Ca(2+) influx was accompanied by the inhibition of adenylyl cyclase and by the stimulation of inward rectifier potassium current. In contrast to somatostatin, ET-1 did not inhibit voltage-gated Ca(2+) channels. During prolonged agonist stimulation a gradual recovery of Ca(2+) influx and GH secretion occurred. In somatotrophs treated with pertussis toxin overnight, the ET-1-induced Ca(2+)-mobilizing phase was preserved, but it was followed immediately by facilitated Ca(2+) influx and GH secretion. Both somatostatin- and ET-1-induced inhibitions of adenylyl cyclase activity were abolished in pertussis toxin-treated cells. These results indicate that the transient cross-coupling of Ca(2+)-mobilizing ET(A) receptors to the G(i)/G(o) pathway in somatotrophs provides an effective mechanism to change the rhythm of [Ca(2+)](i) signaling and GH secretion during continuous agonist stimulation.

Comparison of the mutagenicity of exhaust emissions from motor vehicles using leaded and unleaded gasoline as fuel

While unleaded gasoline has the advantage of eliminating lead from automobile exhaust, its potential to reduce the exhaust gas and particles, merits further examination. In the present studies, the concentrations of hydrocarbons (HC) and carbon mono-oxides (CO) in emissions were analyzed on Santana engine Dynamometer under a standard test cycle, and total exhaust particles were collected from engines using leaded and unleaded gasoline. It was found that unleaded gasoline reduced the emissions of CO and HC, and decreased the quantity of vehicle exhaust particulate matters by 60%. With the unleaded gasoline, only 23 kinds of organic substances, adsorbed in the particles, were identified by gas chromatography/mass spectrometer (GC/MS) while 32 components were detected using the leaded gasoline. The results of in vitro Salmonella/microsomal test and micronucleus induction assay in CHL cells indicated that both types of gasoline increased the number of histidine-independent colonies and the frequencies of micronucleus induction; no significant difference was found in their mutagenicity.

Differential regulation of transcription termination occurring at two different sites on the micro-delta gene complex

The progression of polymerases across the micro-delta Ig heavy chain gene complex is characterized by two termination events occurring at different sites on the transcription unit and at different times during B cell differentiation. We have utilized two mouse strains to analyze the regulatory determinants for these events in primary B cells. In the transgenic pmicro.microdeltaRatt strain a 1160 bp intervening DNA segment (the att site) has been inverted. This mutation results in the abrogation of transcription termination that occurs in early B cells. Using a novel method that takes advantage of an internal ribosome entry site we have further restricted the size of the segment that is needed for inducing transcription termination in transfectants. This 200 bp termination-inducing sequence operates in tumor equivalents of early but not mature B cells and the activity is correlated with differential binding of nuclear proteins. To explore the regulatory basis for the change in site of transcription termination upon B cell activation we have examined the microS-/- deletion mutant strain in which the microS poly(A) site has been eliminated. The results suggest that polyadenylation at the microS site plays a dominant but not exclusive role in regulating transcription termination in activated B cells.

The mechanism of activation of NK-cell IFN-gamma production by ligation of CD28

We have investigated the mechanism by which anti-CD28 antibodies activates IFN-gamma production by murine NK cells. These studies reveal that engagement of CD28 alone by this antibody is a poor activator of this cytokine response. Effective stimulation requires simultaneous ligation of the receptor for Fc (FcgammaRIII, CD16) which on its own is also a poor inducer of murine NK cells. The mechanism by which immobilized anti-CD28 increases IFN-gamma mRNA abundance involves both upregulation of transcription as well as induction of mRNA stabilization. However, the elevation of transcription is not as evident as that induced by IL-12 which, in contrast, does not induce message stabilization. Thus ligation of CD28 in the presence of IL-12 results in a synergistic increase in production of the cytokine. Using this assay we have also determined that immobilized anti-CD28 cannot induce resting NK cells to produce IFN-gamma. In contrast, the same cells can be induced by BCL1-C11 tumor cells that express high amounts of the CD28 ligand, B7-2. These studies provide important insights into the ability of cells bearing counter-receptor for CD28 to activate NK cell-cytokine production in vivo.

Recognition of multiple patterns of DNA sites by Drosophila homeodomain protein Bicoid

Our previous studies demonstrated that the Drosophila homeodomain protein, Bicoid (Bcd), binds DNA cooperatively. In this study, we determined the patterns of adjacent DNA sites required for cooperative recognition by Bcd. Our in vitro selection and biochemical experiments demonstrated that Bcd binds preferentially to both head-to-head and tail-to-tail symmetric sites that are separated by short spacing. An increase in the spacing reduces the strict requirement of symmetric patterns of adjacent sites, permitting Bcd to recognize tandem repeat sites cooperatively. Our further experiments in vivo showed that the only pair of optimally spaced symmetric Bcd sites in a hunchback (hb) enhancer element contributes the most to transcriptional activation by Bcd, demonstrating the biological importance of the binding site patterns revealed by our in vitro selection studies.

Contributions to gene activation by multiple functions of Bicoid

Bicoid is a Drosophila morphogenetic protein required for the development of anterior structures in the embryo. To gain a better understanding of how Bicoid works as a transcriptional activator, we systematically analysed various functions of Bicoid required for gene activation. We provide evidence suggesting that Bicoid is an intrinsically weak activator. First, our biochemical experiments demonstrate that the Bicoid-DNA complexes are very unstable, suggesting a weak DNA-binding function of Bicoid. This idea is further supported by our experiments demonstrating that the same number of LexA-Bicoid fusion molecules can activate transcription more effectively from LexA sites than from Bicoid sites. Secondly, we demonstrate that transcriptional activation by the weak activator Bicoid is readily influenced by the local enhancer environment. These influences are decreased when the Bicoid function is enforced by attaching to it either a known dimerization domain or the strong activation domain VP16. VP16 can also compensate for the loss of some Bicoid sites in an enhancer element. Our experiments demonstrate that the outcome of transcriptional activation by Bicoid is determined by multiple weak functions that are interconnected, a finding that can further help us to understand how this morphogenetic protein achieves its molecular functions.

Pharmacological properties of traditional medicines. XXV. Effects of ephedrine, amygdalin, glycyrrhizin, gypsum and their combinations on body temperature and body fluid

Effects of ephedrine, amygdalin, glycyrrhizin, gypsum and their combinations on body temperature and body fluid were studied in rats using the method developed in our previous reports. Ephedrine significantly increased respiratory evaporative water loss and heat loss in response to a marked elevation of body temperature. There was a small but significant increase in body temperature when amygdalin was orally given rats at a dose of 46.32 mg/kg. Glycyrrhizin and gypsum were unable to affect body temperature. However, gypsum was able to prevent the increased action of ephedrine on body temperature, amygdalin exhibited a preventive tendency to it, and glycyrrhizin did not affect it. The results are in good agreement with classical claims of Makyo-kanseki-to and the related crude drugs in traditional medicine. Moreover, a combination of the four components reproduced the effects of Makyo-kanseki-to on body temperature and body fluid. This report suggests that the co-administration of ephedrine and gypsum is physiologically more desirable than ephedrine alone for dry-type asthmatic patients with a fever. Also, it experimentally supports the clinical efficacy of Makyo-kanseki-to.

Effect of upstream RNA processing on selection of mu S versus mu M poly(A) sites

All of the regulatory factors responsible for augmenting microseconds mRNA levels preceding the dramatic increase in secretory IgM production upon B cell activation has not been totally elucidated. Whereas previous experiments have centered on the region of the gene specifying the choice between splicing to mu M exons versus selection of the mu S poly(A) site, we have found that upstream sequences within the Cmu gene, specifically the Cmu 4 acceptor splice site together with intronic sequences between the Cmu 3++ and Cmu 4 exons, play an important role in dictating the precision or the extent of splicing to the mu M exons even under conditions in which functional polyadenylation factors should be in excess. Therefore, splicing of upstream exons can affect remotely located downstream exons. These findings suggest that regulation of differential mu S/mu M mRNA expression may involve general processing enzymes that recognize specific cis -regulatory sequences residing within the body of the mu gene and account for the unique ability of activated B cells to secrete copious amounts of IgM.

Pharmacological properties of traditional medicines. XXIV. Classification of antiasthmatics based on constitutional predispositions

It is commonly accepted that bronchial asthma or rhinitis accompanies disorders in body fluids and body temperature. The effects of ephedrine and the traditional antiasthmatics "Makyo-kanseki-to" and "Goko-to" were therefore studied on such constitutional predispositions as insensible perspiration and body temperature. Ephedrine markedly increased body temperature and exhibited a strong increased action on respiratory insensible perspiration, whereas Makyo-kanseki-to and Goko-to not only prevented the elevation of body temperature, but also increased respiratory insensible perspiration following the reduction of non-evaporative heat loss from the body surface. Thus, the diagnostic criteria of these two medicines used to treat hot-type asthma or dry cough were experimentally determined. The results also suggest that there is a great possibility that the administration of antiasthmatics may elicit side effects or make diseases worse unless their actions on constitutional predispositions are taken into account, such as body temperature and body fluids.

A new experimental device for the measurement of moisture emission and heat release from respiratory organs and body surface

A new experimental device was developed to investigate respiratory diseases. The moisture and heat released from respiratory organs and the body surface of a rat were determined by means of this device as well as the rectal temperature. The high recovery of results was statistically confirmed, and the measured values at various environmental temperatures were significantly different from each other. Some standard drugs, such as ephedrine, aminophylline and chlorpromazine, were examined. Their stimulant or depressant actions were clearly observed. The results of some traditional medicines for the treatment of rhinitis and bronchial asthma from this measuring system were consistent with their clinical applications. These results suggest that this new experimental system is not only effective in the experimental understanding of cold-hot syndrome, but also contributes to the evaluation of the effects of traditional medicines.

[Effect of HE-NE laser acupuncture on the spleen in rats]

The splenic sinuses, lymphocytes and antigen presenting cells in the spleen of rat stimulated by He-Ne laser acupuncture were observed by using TEM to investigate the ultrastructural changes of them. The width of endothelial interstice was increased, hence a lot of blood cells oozed out of the splenic sinuses. There were numerous activated T cells which contained abundant mitochondria and ribosome in the periarterial lymphatic sheaths. The B cells were gradually differentiated into large lymphocytes, immature and mature plasmatic cells with a lot of endoplasmic reticula. They were prominently increased in the splenic nodules. The macrophages had short processes with numerous folds and microvilli and tended to neighboring lymphocytes. The nucleus pores were increased. There were a lot of vacuoles, phagosome and mitochondria were closed to macrophages and lymphocytes. In conclusion the activities of the cellular immunity and humoral immunity were enhanced by laser.

The effect of NK cell activation by tumor cells on antigen-specific antibody responses

In addition to mediating direct cytotoxicity, NK cells can exert regulatory effects on specific immune responses. For example, injection of poly (I:C) can alter specific Ab responses, which is attributable to the production of IFN-gamma by NK cells. To test whether direct activation of NK cells can exert the same effect, we have injected, at the same time as Ag challenge, BCL1-C11 tumor cells, which are highly effective inducers of IFN-gamma production by NK cells. The results show a specific enhancement of the IgG2a response, which does not occur with a tumor (70Z/3) that does not induce IFN-gamma production. This enhancement is NK cell and IL-12 dependent. However, BCL1-C11 cells cannot directly induce IL-12 production in peritoneal exudate cells (PECs). On the other hand, PECs from tumor-treated mice produce IL-12 in response to LPS, suggesting that they are primed in vivo. Furthermore, the IL-12 production is NK cell and IFN-gamma dependent. These results indicate that if tumor cells can directly activate NK cells to produce IFN-gamma, this cytokine initiates an amplification loop by activating macrophages to produce IL-12, which in turn activates NK cells further, resulting in the alteration of the isotype distribution of specific Ab responses. Production of the appropriate Ab isotype should enhance Ab-dependent cellular cytotoxicity against targets mediated by NK cells, implicating their role(s) in the specific immune response as well as the initial nonspecific phase.

The effect of NK cell activation by tumor cells on antigen-specific antibody responses

In addition to mediating direct cytotoxicity, NK cells can exert regulatory effects on specific immune responses. For example, injection of poly (I:C) can alter specific Ab responses, which is attributable to the production of IFN-gamma by NK cells. To test whether direct activation of NK cells can exert the same effect, we have injected, at the same time as Ag challenge, BCL1-C11 tumor cells, which are highly effective inducers of IFN-gamma production by NK cells. The results show a specific enhancement of the IgG2a response, which does not occur with a tumor (70Z/3) that does not induce IFN-gamma production. This enhancement is NK cell and IL-12 dependent. However, BCL1-C11 cells cannot directly induce IL-12 production in peritoneal exudate cells (PECs). On the other hand, PECs from tumor-treated mice produce IL-12 in response to LPS, suggesting that they are primed in vivo. Furthermore, the IL-12 production is NK cell and IFN-gamma dependent. These results indicate that if tumor cells can directly activate NK cells to produce IFN-gamma, this cytokine initiates an amplification loop by activating macrophages to produce IL-12, which in turn activates NK cells further, resulting in the alteration of the isotype distribution of specific Ab responses. Production of the appropriate Ab isotype should enhance Ab-dependent cellular cytotoxicity against targets mediated by NK cells, implicating their role(s) in the specific immune response as well as the initial nonspecific phase.

Effect of the presence of transgenic H and L chain genes on B cell development and allelic exclusion

The expression of various components of the antigen receptor is closely associated with the developmental progression of B lymphocytes. For this reason, introduction of rearranged Ig transgenes exerts profound effects on B cell development. In these studies we show that the presence of transgenes for both mu and delta H as well as L chains accelerates the rate of B cell maturation resulting in the appearance of large numbers of IgD-expressing B lymphocytes in vitro that are otherwise undetectable. In addition, allelic exclusion, normally exerted very effectively by these particular transgenes (carried in the MD-3 strain), was lost in the long-term bone marrow cultures. These findings can be recapitulated in vivo by serial adoptive transfers of bone marrow cells from the transgenic animals into lethally irradiated recipients. We conclude from these studies that allelic exclusion is not necessarily mediated by any one event but may be a result of the integrated occurrence of Ig H chain gene rearrangement, accumulation of transcription factors, along with the ordered progression of B cell differentiation under the influence of the appropriate inductive microenvironment. These findings may account for at least some of the observed cases of allelic inclusion in transgenic animals.

[Clinial study of "qingjunyin" detoxification for the treatment of heroin addicts]

To evaluate the efficacy of treatment of heroin addicts (n = 100) by "Qingjunyin" (QJY) detoxification (10 days program). Methadone detoxification (10 days program) group (n = 50) and colonidine treated group (n = 50) serve as controls. QJY group is given 180 ml P. O daily. The dosage of the two comparatine groups is given according to Documentation, the method of abserving the treatment protocols and detoxification standard is according to current regulation. The scores of abstinence syndrome in QJY detoxification group are lower than those in colonidine treated group in the first three days of potocol, but this difference disappear in the late stage of treatment. While QJY detoxification is effective as methadone detoxification in the control of abstinece syndrome during the first five days of treatment but the difference in the scores of abstinence syndrome between QJY and methadone group is observed during the late five days of protocol. QJY does not result in potential dependence and has definite curative effect in the treatment of heroin addiction.

Regulation of IgM and IgD heavy chain gene expression: effect of abrogation of intergenic transcriptional termination

Early IgM+ B cells express little or no membrane IgD due to the low abundance of delta mRNA. Extensive transcriptional termination regulated by sequences in the intronic region between mu and delta heavy chain genes may be the primary reason for the lack of delta gene transcription. We have examined the effect of deletion of these sequences on the regulation of IgM and IgD heavy chain gene expression in transfectants as well as mice carrying this otherwise intact transgene. By run-on transcriptional measurement, we show that the delta exons are transcribed in bone marrow B cells from these transgenic mice. However, in spite of the induced premature synthesis of the full-length mu-delta transcript in pre-B cells, processing to delta mRNA does not occur until the lymphocytes express cell surface IgM. Therefore, during B cell development, synthesis of the full-length transcript is a necessary but not sufficient condition for initiation of delta mRNA synthesis. Furthermore, unexpectedly, the abrogation of transcriptional termination was found to also affect the processing of the primary transcript to microM mRNA. These results show that expression of IgD in primary B cells is stringently regulated and closely linked to IgM expression.

Regulation of IgM and IgD heavy chain gene expression: effect of abrogation of intergenic transcriptional termination

Early IgM+ B cells express little or no membrane IgD due to the low abundance of delta mRNA. Extensive transcriptional termination regulated by sequences in the intronic region between mu and delta heavy chain genes may be the primary reason for the lack of delta gene transcription. We have examined the effect of deletion of these sequences on the regulation of IgM and IgD heavy chain gene expression in transfectants as well as mice carrying this otherwise intact transgene. By run-on transcriptional measurement, we show that the delta exons are transcribed in bone marrow B cells from these transgenic mice. However, in spite of the induced premature synthesis of the full-length mu-delta transcript in pre-B cells, processing to delta mRNA does not occur until the lymphocytes express cell surface IgM. Therefore, during B cell development, synthesis of the full-length transcript is a necessary but not sufficient condition for initiation of delta mRNA synthesis. Furthermore, unexpectedly, the abrogation of transcriptional termination was found to also affect the processing of the primary transcript to microM mRNA. These results show that expression of IgD in primary B cells is stringently regulated and closely linked to IgM expression.

Sequences outside the homeodomain of bicoid are required for protein-protein interaction

The Drosophila morphogenetic protein Bicoid (Bcd) is required for the development of anterior structures of the embryo. Bcd, a homeodomain protein, is distributed as an anterior-to-posterior gradient in the embryo. It stimulates the expression of the hunchback (hb) gene in the anterior half in an all-or-none fashion. We have recently shown that Bcd binds cooperatively to a hb enhancer element and proposed that cooperative DNA binding is facilitated by an interaction between Bcd molecules. In this report, we further analyze the interaction between Bcd molecules and define regions important for protein-protein interaction. We show that the homeodomain of Bcd alone fails to interact with another Bcd molecule efficiently. The protein sequence flanking either side of the homeodomain restores the protein-protein interaction function. Mutations in the homeodomain that affect DNA binding do not adversely affect the protein-protein interaction function, suggesting that the surfaces for DNA binding and protein-protein interaction are separable. Finally, we demonstrate that the homeodomain of Bcd alone, unlike the intact Bcd, fails to bind DNA cooperatively. These results further support the notion that cooperative DNA binding is facilitated by the interaction between Bcd molecules. They strongly suggest that protein-protein interaction is an important property of Bcd for its biological activities.

The Drosophila morphogenetic protein Bicoid binds DNA cooperatively

The Drosophila morphogenetic protein Bicoid, encoded by the maternal gene bicoid, is required for the development of the anterior structures in the embryo. Bicoid, a transcriptional activator containing a homeodomain, is distributed in an anterior-to-posterior gradient in the embryo. In response to this gradient, the zygotic gene hunchback is expressed uniformly in the anterior half of the embryo in a nearly all-or-none manner. In this report we demonstrate that a recombinant Bicoid protein binds cooperatively to its sites within a hunchback enhancer element. A less than 4-fold increase in Bicoid concentration is sufficient to achieve an unbound/bound transition in DNA binding. Using various biochemical and genetic methods we further demonstrate that Bicoid molecules can interact with each other. Our results are consistent with previous studies performed in the embryo, and they suggest that one mechanism to achieve a sharp on/off switch of gene expression in response to a morphogenetic gradient is cooperative DNA binding facilitated by protein-protein interaction.

The role of NK cells during in vivo antigen-specific antibody responses

Investigations into the role of NK cells in regulating Ab responses have yielded variable results, some suggesting that NK cells can down-regulate Ag-specific Ig production and others proposing an enhancing effect. These apparently inconsistent findings may stem partially from the specificity of reagents used in purifying cell populations and/or the nature of the in vitro systems used to study these events. We chose to investigate the ability of either resting or poly(I:C)-activated NK cells to alter an in vivo Ab response in mice given a T-independent (TNP-LPS) or T-dependent (TNP-keyhole limpet hemocyanin (KLH)) Ag. By using a more specific Ab, anti-NK-1.1, to deplete NK cells, we were able to clearly show that resting, endogenous NK cells do not affect either type of response, as measured by serum Ag-specific Ig levels quantitated by isotype-specific ELISA. In contrast, activation of NK cells by poly(I:C) increased Ag-specific IgC2a as well as IgG1 levels. Interestingly, only the effect on IgG2a production is reversible by depletion of NK cells.