Ectopic pregnancy early diagnosis markers

Ectopic pregnancy (EP) is a high-risk medical condition with an incidence of 1.9% in reported pregnancies, and has proven to be the most common cause of pregnancy-related deaths in the first trimester. The clinical symptoms can mimic non-EP conditions, thus creating a challenge for developing diagnostic criteria and new diagnostic tools. Early diagnosis of ectopic pregnancy is essential in order to minimize the morbidity and to assess the need for urgent surgical intervention. Currently, ultrasound and serum biomarkers are used by clinicians for early detection and diagnosis. This review summarizes and comments on the available literature on the various markers including their utility and their statistical parameters.

In vitro immunomodulatory activity of ruthenium complexes

OBJECTIVE AND DESIGN

We have explored the in vitro immunomodulatory effects of pure ruthenium red and a series of pyridine and imidazole substituted ruthenium complexes (RCs).

MATERIAL

Human peripheral blood lymphocytes and purified T cells were used in these studies along with various cell lines.

METHODS

Cells were treated with dilutions of RCs and assessed in various assays of immune function, cytotoxicity and cell cycle progression.

RESULTS

RCs efficiently blocked T cell receptor (TCR)-mediated stimulation (IC(50)'s in the low nM range) of human peripheral blood lymphocytes (hPBL) by various agents, including tetanus toxoid, alloantigens, superantigens, and receptor-specific antibodies. RCs are not cytotoxic to T cells. Antiproliferative activity was also observed for B cells. Some non-lymphoid cell lines or primary cultures showed sensitivity to the RCs, but only at higher concentrations. The inhibitory effect on human T cells was assessed and demonstrated at the level of proliferation (DNA synthesis), IL-2 secretion, and IL-2 receptor (CD25) upregulation. RCs also inhibited IL-2-mediated proliferation of antigen-induced T-cell blasts and the IL-2-dependent T cell line Kit-225. Cell cycle analysis indicates that RCs inhibit the progression of activated T cells from G(0)/G(1) to S phase.

CONCLUSIONS

Since the mechanism of T cell inhibition by RCs appears to be different than that of rapamycin (RAP) or cyclosporin A (CsA), they may provide a new tool to investigate intracellular signaling in T cells, and may present novel opportunities for immunosuppression

Evidence for different aetiologies of low estradiol response to FSH: age-related accelerated luteinization of follicles or presence of ovarian autoantibodies

BACKGROUND

We found granulosa cells of low responders (LR) expressed more LH receptors, suggesting that follicles were more luteinized than normal responders (NR). The objectives were to test the hypothesis that follicles of LR were more luteinized than follicles of NR, and to determine if LR with (LR+) and without (LR-) ovarian antibodies differed.

METHODS

Hormone levels and ovarian autoantibodies (OVAB) were measured in follicular fluid from mature follicles (>17 mm), and in serum obtained on the day of oocyte retrieval during controlled ovarian stimulation. The gonadotrophin response was defined as a ratio of peak estradiol/number of FSH ampoules.

RESULTS

NR (32.5 +/- 4.6 years; n = 11) were similar in age to LR+ (33.4 +/- 4.2 years; n = 9) and were younger than LR- (37.1 +/- 3.8 years; n = 12) (P = 0.03). Likewise, dehydroepiandrosterone sulphate was lower in LR- compared with LR+ or NR (P < 0.01). FSH, progesterone, inhibin-A and vascular endothelial growth factor levels were higher in follicular fluid of LR than NR. LR- and LR+ differed. For example, the follicular fluid progesterone/estradiol ratio was similar in NR (11.1 +/- 8.9) and LR+ (9.8 +/- 6.6) but was lower than LR- (22.9 +/- 19.6) (P = 0.05). Serum hormone levels did not reflect follicular fluid hormone profiles.

CONCLUSIONS

In the absence of ovarian antibodies, low responses are associated with higher age and accelerated luteinization of mature follicles, rather than diminished responsiveness. Ovarian antibody may be an additional tool to predict and individualize treatment regimens in poor responders.

CHK down-regulates SCF/KL-activated Lyn kinase activity in Mo7e megakaryocytic cells

The Csk Homologous Kinase (CHK) has been shown to have an enzymatic activity similar to the tyrosine kinase Csk in that it down-regulates Src family kinase activity by causing phosphorylation of the Src C-terminal tyrosine residue. In megakaryocytic Mo7e cells, CHK associates with a specific phosphotyrosine juxtamembrane sequence of the SCF/KL-activated c-Kit receptor. Here, we show that in Mo7e cells, the major Src family kinase activity is p53/56(Lyn). Studies using immobilized c-Kit phosphopeptides show that Lyn is able to specifically associate with the tyrosine-phosphorylated juxtamembrane 568Y*VY*IDPT sequence of c-Kit which has previously been shown to associate with CHK. In cells over-expressing CHK by means of a recombinant vaccinia virus, we observed an elimination of the SCF/KL-stimulated Lyn kinase peak of activity observed at 2-5 minutes in cells infected with the helper T7-expressing vaccinia virus by itself. Examination of total tyrosine phosphorylation by Western blotting showed that over-expression of CHK resulted in a reduction in the levels of tyrosine phosphorylations in the range of 50-60 kDa, but had no apparent effect on c-Kit autophosphorylation. Taken together, these findings show that CHK is able to down-regulate SCF/KL-stimulated Lyn activity in megakaryocytes.

NRP/B, a novel nuclear matrix protein, associates with p110(RB) and is involved in neuronal differentiation

The nuclear matrix is defined as the insoluble framework of the nucleus and has been implicated in the regulation of gene expression, the cell cycle, and nuclear structural integrity via linkage to intermediate filaments of the cytoskeleton. We have discovered a novel nuclear matrix protein, NRP/B (nuclear restricted protein/brain), which contains two major structural elements: a BTB domain-like structure in the predicted NH2 terminus, and a "kelch motif" in the predicted COOH-terminal domain. NRP/B mRNA (5.5 kb) is predominantly expressed in human fetal and adult brain with minor expression in kidney and pancreas. During mouse embryogenesis, NRP/B mRNA expression is upregulated in the nervous system. The NRP/B protein is expressed in rat primary hippocampal neurons, but not in primary astrocytes. NRP/B expression was upregulated during the differentiation of murine Neuro 2A and human SH-SY5Y neuroblastoma cells. Overexpression of NRP/B in these cells augmented neuronal process formation. Treatment with antisense NRP/B oligodeoxynucleotides inhibited the neurite development of rat primary hippocampal neurons as well as the neuronal process formation during neuronal differentiation of PC-12 cells. Since the hypophosphorylated form of retinoblastoma protein (p110(RB)) is found to be associated with the nuclear matrix and overexpression of p110(RB) induces neuronal differentiation, we investigated whether NRP/B is associated with p110(RB). Both in vivo and in vitro experiments demonstrate that NRP/B can be phosphorylated and can bind to the functionally active hypophosphorylated form of the p110(RB) during neuronal differentiation of SH-SY5Y neuroblastoma cells induced by retinoic acid. Our studies indicate that NRP/B is a novel nuclear matrix protein, specifically expressed in primary neurons, that interacts with p110(RB) and participates in the regulation of neuronal process formation.

Direct association of Csk homologous kinase (CHK) with the diphosphorylated site Tyr568/570 of the activated c-KIT in megakaryocytes

The Csk homologous kinase (CHK), formerly MATK, has previously been shown to bind to activated c-KIT. In this report, we characterize the binding of SH2(CHK) to specific phosphotyrosine sites on the c-KIT protein sequence. Phosphopeptide inhibition of the in vitro interaction of SH2(CHK)-glutathione S-transferase fusion protein/c-KIT from SCF/KL-treated Mo7e megakaryocytic cells indicated that two sites on c-KIT were able to bind SH2(CHK). These sites were the Tyr568/570 diphosphorylated sequence and the monophosphorylated Tyr721 sequence. To confirm this, we precipitated native CHK from cellular extracts using phosphorylated peptides linked to Affi-Gel 15. In addition, purified SH2(CHK)-glutathione S-transferase fusion protein was precipitated with the same peptide beads. All of the peptide bead-binding studies were consistent with the direct binding of SH2(CHK) to phosphorylated Tyr568/570 and Tyr721 sites. Binding of FYN and SHC to the diphosphorylated Tyr568/570 site was observed, while binding of Csk to this site was not observed. The SH2(CHK) binding to the two sites is direct and not through phosphorylated intermediates such as FYN or SHC. Site-directed mutagenesis of the full-length c-KIT cDNA followed by transient transfection indicated that only the Tyr568/570, and not the Tyr721, is able to bind SH2(CHK). This indicates that CHK binds to the same site on c-KIT to which FYN binds, possibly bringing the two into proximity on associated c-KIT subunits and leading to the down-regulation of FYN by CHK.

The MATK tyrosine kinase interacts in a specific and SH2-dependent manner with c-Kit

We have cloned a protein tyrosine kinase, MATK, which is expressed abundantly in megakaryocytes and the brain. We investigated whether MATK participates in the c-Kit ligand/stem cell factor (KL/SCF) signaling pathway in the megakaryocytic cell line CMK. After KL/SCF stimulation, five major proteins of molecular masses of 145, 113, 92, 76, and 63 kDa were rapidly and transiently tyrosine-phosphorylated in a time-dependent manner, peaking within 5 min, and returning to basal levels within 60 min. To study the role of MATK in the KL/SCF signaling pathway, glutathione S-transferase (GST) fusion proteins containing SH2 and SH3 domains of MATK were cloned, expressed in Escherichia coli, and purified. MATK-SH2, but not MATK-SH3, precipitated the tyrosine-phosphorylated c-Kit (molecular mass of 145 kDa) in KL/SCF-stimulated CMK cells. Other GST fusion proteins containing the SH2 domain of p85 of phosphatidylinositol 3-kinase, phospholipase C gamma-1, and ras-GAP also precipitated c-Kit. The tyrosine-phosphorylated c-Kit was co-immunoprecipitated with anti-MATK and anti-p85 antibodies in KL/SCF-stimulated CMK cells, but not in granulocyte-macrophage colony stimulating factor or interleukin-6-stimulated cells, suggesting receptor specificity. These results indicate that MATK associates with the c-Kit receptor following specific stimulation by KL/SCF via its SH2 domain and likely participates in transduction of growth signals induced by this cytokine in megakaryocytes.

Purification of a major tyrosine kinase from RBL-2H3 cells phosphorylating Fc epsilon RI gamma-cytoplasmic domain and identification as the Btk tyrosine kinase

Immunoglobulin E high affinity receptor-mediated signal transduction in mast cells results in a number of protein tyrosine kinases being activated as very early events in the process leading to degranulation. Some of these, such as the src kinases and the syk kinase, are known to be involved in this receptor-associated activation. In this paper we describe the search for other activation-associated tyrosine kinases by the ability to phosphorylate a cytoplasmic domain peptide of the Fc epsilon RI gamma-subunit. In utilizing a purification step previously used to isolate the 72 kDa syk kinase, we detected another kinase of molecular weight 79 kDa which we designated cd gamma kinase. The kinase was purified to near homogeneity by Heparin-agarose, Mono Q, and CM Sepharose chromatographies. The yield of enzyme was approx. 200 micrograms/10(9) cells. We characterized this kinase by its ability to phosphorylate both the cd gamma peptide (Km = 0.2 mM) and the cytoplasmic fragment of the Band III protein. The cd gamma kinase was distinguished from syk by inability to be precipitated by anti-syk antiserum and by partial peptide mapping. Cd gamma kinase was also distinguished from syk by cd gamma peptide and Band III substrate specificity. We identified the cd gamma kinase by Western blotting and by partial phosphopeptide mapping as Btk, the B-cell tyrosine kinase found to be defective in X-linked agammaglobulinemia.

Calcium channel antagonist peptides define several components of transmitter release in the hippocampus

The use of subtype-selective voltage-sensitive calcium channel (VSCC) antagonists has established that neurotransmitter release in mammalian brain is mediated by N-like and P-like VSCCs, and that other subtypes also contribute significantly. To determine the roles presynaptic VSCCs play in nervous system function and to evaluate the therapeutic potential of their selective inhibition, it is necessary to define further the contributions of VSCC subtypes to neurotransmitter release. The novel conopeptide, SNX-230 (omega-conopeptide MVIIC), has revealed a new VSCC subtype, the Q-type, in cerebellar granule cells. We have compared the effects of SNX-230 on release of tritiated D-aspartate ([3H]D-Asp; a non-metabolizable analog of glutamate), gamma-aminobutyric acid ([3H]GABA), and norepinephrine ([3H]NE) from rat hippocampal slices to those of the N-type VSCC blocker, SNX-111 (omega-conopeptide MVIIA), and the P-type blocker, omega-agatoxin-IVA (AgaIVA). SNX-230 blocks both [3H]D-Asp and [3H]GABA release completely, whereas AgaIVA blocks them potently but partially and SNX-111 has no effect. These results suggest that glutamate and GABA release are mediated by two VSCC subtypes, a P-type and another, perhaps Q-like. SNX-111 blocks [3H]NE release potently but partially, while SNX-230 blockade is complete, consisting of one very potent phase and one less potent phase. AgaIVA also blocks [3H]NE release potently but partially. These results suggest that at least two VSCC subtypes, an N-type and a novel non-N-type, mediate NE release. Pair-wise combinations of the three ligands indicate that at least three pharmacologically distinct components comprise [3H]NE release in the hippocampus.

Implanted IgE-Fc epsilon R complexes elicit IgE-mediated activation of RBL-2H cells

The high-affinity receptor for IgE (Fc epsilon R) is the cellular trigger of the antigen-induced activation of mast cells and basophils. To examine the functional integrity of Fc epsilon R, we have adopted a protein implantation procedure whereby the purified receptor complex was coreconstituted with Sendai virus envelopes. The latter promoted fusion of the hybrid vesicles with recipient cells such as rat basophilic leukemia, RBL-2H3, thus serving as a vehicle for the receptor. The implanted Fc epsilon R was complexed with 125I-labeled mouse IgE (anti-DNP) to permit receptor quantification as well as specific triggering by DNP20BSA. Implantation in the presence of unlabeled rat IgE, which blocked the native receptors on the recipient RBL-2H3 cells, resulted in incorporation of up to 15 ng of receptor-bound IgE/10(6) cells. This was roughly equivalent in amount to 10-20% of the native receptors on such cells. The exocytosis which was triggered in the recipient cells by reagents that specifically recognized the implanted IgE reached between 15 and 50% of the maximal response. Various treatments that interfered with the activities of the viral envelopes reduced both receptor incorporation (3-5-fold) and cell degranulation (3-10-fold). These included separation of the receptor from the reconstituted envelopes, addition of serum to the incubation mixture (to inhibit vesicle-cell binding), and trypsinization of the virus (to inhibit vesicle-cell fusion). Poly(ethylene glycol) 8000 (4%) enhanced both the incorporation of the receptor and its functional responses. These treatments distinguished between real incorporation of IgE-Fc epsilon R complexes and other mechanisms of 125I-IgE association with the recipient cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium specificity of the antigen-induced channels in rat basophilic leukemia cells

Ion channels, activated upon IgE-Fc epsilon receptor aggregation by specific antigen, were studied in micropipet-supported lipid bilayers. These bilayers were reconstituted with purified IgE-Fc epsilon receptor complex and the intact 110-kDa channel-forming protein, both isolated from plasma membranes of rat basophilic leukemia cells (line RBL-2H3). In order to identify the current carrier through these ion channels and to determine their ion selectivity, we investigated the currents flowing through the IgE-Fc epsilon receptor gated channels in the presence of a gradient of Ca2+ ions. Thus, the solution in which the micropipet-supported bilayer was immersed contained 1.8 mM CaCl2, while the interior of the micropipet contained 0.1 microM Ca2+ (buffered with EGTA). Both solutions also contained 150 mM of a monovalent cation chloride salt (either K+ or Na+). The currents induced upon specific aggregation of the IgE (by either antigen or anti-IgE antibodies) were examined over a range of potentials imposed on the bilayer. The type of conductance event most frequently observed under the employed experimental conditions was a channel that has a slope conductance of 3 pS and a reversal potential practically identical with the calculated value for the reversal potential of calcium (134 +/- 11 mV in the presence of sodium, 125 +/- 13 mV in the presence of potassium). These results indicate that this channel is highly selective for calcium against the monovalent cations sodium and potassium. This same channel has a conductance of 4-5 pS in the presence of symmetrical solutions containing only 100 mM CaCl2 and 8 pS in the presence of 0.5 M NaCl with no calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Reconstitution of fusogenic Sendai virus envelopes by the use of the detergent chaps

Sendai virus envelopes have been a useful tool in studying the mechanism of membrane-membrane fusion and have served as a vehicle for introducing foreign molecules (e.g., membrane proteins) into recipient cells. Reconstituted Sendai virus envelopes are routinely obtained following solubilization of virus particles with Triton X-100. This detergent has a low critical micellar concentration which precludes it from being the best detergent of choice in reconstitution studies. Nevertheless, it has remained in use since other detergents such as sodium deoxycholate and sodium cholate rendered the resultant vesicles inactive. Triton X-100 may be suboptimal for studies of some proteins that need be coreconstituted with the viral envelopes. Thus, alternative advantageous detergents, which retain the envelope fusogenic activity, have been sought. In this study we show that the synthetic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (Chaps) effectively solubilizes the Sendai virions, and that the vesicles formed by simple reconstitution protocols appear structurally and biochemically similar to those obtained with Triton X-100. The resultant vesicles retain functional integrity as assessed in both fusion and hemolysis assays. This protocol seems to be useful in sendai envelope-mediated reimplantation of Fc epsilon receptors into the plasma membranes of rat basophilic leukemia cells.

Activation of rat basophilic leukemia cells. Temporal identification of the signal calcium influx mediated by the receptor-operated channel pathway

Antigen-induced 45calcium influx into rat basophilic leukemia (RBL) cells was examined with emphasis on the early time domain under conditions that exclude loss of the cation during the subsequent washing step. Such preparations demonstrate a distinct, temporally separate influx peaking at 3 min, followed by a substantial efflux. This internalized 45Ca2+ approaches millimolar total intracellular concentration and is therefore either sequestered or becomes bound to intracellular components (proteins). The amplitude of this influx is linearly proportional to IgE-receptor occupancy at low receptor occupancies, and is sensitive to the anti-allergic drug cromolyn. Furthermore, the timing of both the maximal uptake and the maximal susceptibility to cromolyn correlates with the Quin-2 signal in these cells, and the initial degranulation pattern bears some resemblance to trends in the 45Ca2+ uptake curve. These qualities suggest that the early peak at 2-3 min, rather than any later 45Ca2+ uptake, comprises the initial signalling Ca2+ pool. Maximal apparent inhibition by cromolyn for 45Ca2+ uptake was about 65% and required a 10-15-min preincubation with the cells. The inhibitory effect was limited to the peak at 3 min, suggesting that tracer incorporation beyond 5-6 min largely involves other pools or pathways, triggered by receptor aggregation, yet only indirectly related to channel activity or to the signal proper. A quantitative similarity was found between the early peak measured on intact cells and the single channel conductance measured on reconstituted planar bilayers containing the purified receptor for IgE and the purified cromolyn-binding protein [Corcia, A. et al. (1986) EM BO J. 5, 849-854]. This, as well as the effects of cromolyn, support the assumption that cromolyn-binding protein is a major constituent involved in this early influx, or that influx is a principal pathway for the signaling calcium mass.

Hydrocortisone inhibits antigen-induced rise in intracellular free calcium concentration and abolishes leukotriene C4 production in leukemic basophils

Antigenic stimulation of rat basophilic leukemia cells (RBL-3H3) elevates intracellular free Ca2+ concentration ([Ca2+]i) and induces production of leukotriene C4 (LTC4). This model was used to examine the role of Ca2+ in LTC4 formation, and inhibition by hydrocortisone (HC). HC, at a physiological concentration (2 x 10(-7) M), selectively prevented the stimulatory effect of the antigen on LTC4 production whereas the response to calcium ionophore (A23187) remained unimpaired. The inhibition by HC was time-dependent: half maximal response was reached at 2 hour and maximal response at 3 hours. Addition of arachidonic acid (3 micrograms/ml) did not overcome the inhibitory action of HC. An elevated [Ca2+]i is known to be essential for the activation of both 5-lipoxygenase and phospholipase A2. The stimulatory effect of the antigen on LTC4 production was abolished when the cells were incubated in Ca2+-deficient medium. Likewise, calcium ionophore stimulation shows dependence on extracellular Ca2+. Half maximal stimulation by the antigen and calcium ionophore was observed at external Ca2+ concentration of 150 microM and 40 microM respectively. Treatment with HC largely prevented the antigen-induced rise in [Ca2+]i, measured by Quin 2. In addition, HC reduced by 70% the accumulation of 45Ca2+ induced by the antigen. Collectively, these results demonstrate for the first time that HC reduces antigen-induced elevation of [Ca2+]i, and this may be associated with the inhibitory action of HC on LTC4 formation. This property could be partly responsible for the antiallergic and antiinflammatory activities of HC.

[The relationship between Ca++ ions and a protein specific to cromolyn in the degranulation of mast cells and basophils in the rat]

Previous research has shown that cromolyn (disodium cromoglycate) binds specifically to the membrane of rat mast and basophil leukemia (RBL) cells, forming a ternary complex with Ca++, blocking of the Ca++ results in inhibition of histamine release upon immunologic triggering. The specific cromolyn binding protein (CBP) has been isolated by using its high affinity form cromolyn. Specific monoclonal anti CBP antibodies have been obtained in mice and polyclonal anti-cromolyn antibodies in rabbits. These antibodies have been used for further purification and characterization of the CBP. Experiments on RBL cell lines have shown that CBP is essential for Ca++ influx and histamine liberation upon immunologic triggering by these cells. Variant CBP deficient RBL do not take up Ca++ and do not degranulate in response to immunologic triggering but their ability to respond normally can be induced by incorporating CBP into their membranes with help of Sendai virus carrier vesicles. This shows that CBP plays a crucial role for the RBL cells Ca++ influx and histamine release following IgE crosslinking.

On the mechanism of sphingomyelin interaction with solubilized membrane proteins

Studies on the high-affinity receptor for IgE from rat basophilic leukemia cells (RBL-2H3) have shown that the phospholipid sphingomyelin remains attached to the protein complex during washing of the affinity immobilized complex under solubilizing conditions. Here we extended these findings and compared the species distribution patterns in sphingomyelin and phosphatidylcholine of the receptor-bound lipids to those of the plasma membrane lipids. FC epsilon-receptor-bound sphingomyelin but not phosphatidylcholine was enriched in long-chain fatty acids. We then examined other membrane proteins with respect to sphingomyelin enrichment. RBL-2H3 cell surface proteins, immobilized on concanavalin A-Sepharose and washed under solubilizing conditions, also showed a two- to six-fold enrichment in the associated sphingomyelin. Similar observations were also derived from other cell types, such as the mouse fibroblast cell line A-9 and the pig kidney epithelial cell line PK-1. Since this has been observed in all the three cell sources, it was suggested that sphingomyelin enrichment in FC epsilon-receptor preparations, although reproducible, was not specific for this protein. That this phenomenon was not specific for a particular protein might also be concluded from experiments that have shown nonhomogenous distribution of sphingomyelin in protein-free lipid-detergent mixtures. These results are compatible with a model whereby the interaction between sphingomyelin and soluble membrane proteins results from preference to nonmicellar phases or to structures with extended hydrophobic domains, probably due to the imperfect fitness of the detergent micelles to properly accomodate these lipids. This feature makes long-chain sphingomyelin a plausible candidate for the lipid responsible for the stabilizing effect that crude lipid preparations exert on the structural and functional properties of some membrane protein, e.g., FC epsilon R.

Phospholipid distribution in the microenvironment of the immunoglobulin E-receptor from rat basophilic leukemia cell membrane

It has been previously found that lipids were required to maintain intact the tetrameric structure of the receptor for immunoglobulin E (IgE) (Fc epsilon R) in detergent solutions [Rivnay, B., Rossi, G., Henkart, M., & Metzger, H. (1984) J. Biol. Chem. 259, 1212-1217, and references cited therein]. Failure of commercially obtained lipids to provide sufficient protection, however, underscored the necessity for development of additional analytical approaches. In order to identify the phospholipid distribution in the intimate natural environment of this receptor, both the plasma membrane vesicles and the ligand-receptor complex (IgE-Fc epsilon R) have been isolated by affinity chromatography. The phospholipids of both preparations were compared. After extensive washing with detergent lipid micelles, IgE-Fc epsilon R retained 0.1-1% of the total phospholipids in the purified plasma membrane. The receptor-bound lipids were shown to contain phosphatidylcholine and sphingomyelin; the content of the latter lipid was enriched 2-5-fold compared with that in the plasma membranes. This pattern was observed with several detergents employed for purification and under a variety of experimental conditions. In light of the general distribution of choline phospholipids in the outer leaflet of plasma membranes, this enrichment may not be a characteristic of this particular receptor exclusively. These observations should be particularly helpful in studies on aggregation-induced functions of the isolated Fc epsilon receptor. In general, the methods employed enable isolation of purified and lipid-protected integral proteins and also provide an appropriate reference source of intact membrane vesicles. These qualities render this approach useful in similar studies of other membrane proteins.

Characterization of the ion channel activity in planar bilayers containing IgE-Fc epsilon receptor and the cromolyn-binding protein

Electric conductance was studied across micropipette-supported planar lipid bilayers, reconstituted with IgE-Fc epsilon receptor and the cromolyn-binding protein (CBP) isolated from membranes of rat basophilic leukemia cells (RBL-2H3). Currents were observed following the addition of aggregating agents, specific for either of the two proteins. The results show that the two proteins are necessary and sufficient for the opening of cation channels. Both aggregation of Fc epsilon receptor via IgE with a specific antigen and of CBP by anti-CBP induce channels with similar conductances and open-time distributions. In the presence of 1.8 mM calcium, the most frequently observed channels have a conductance of 1-2 pS. At 100 mM calcium conductance increased to 4-5 pS. Channels induced by antigen were susceptible to blocking by the anti-allergic drug cromolyn. These results suggest that CBP acts as the core of the cation channel and that the channel conductance and open-time characteristics are independent of the mode of aggregation.

Relationships between epitopes on IgE recognized by defined monoclonal antibodies and by the FC epsilon receptor on basophils

The present study investigated whether the sites on the FC region of the IgE molecule, recognized by different anti-IgE monoclonal antibodies (mAb), are identical to those recognized by the Fc receptor (Fc epsilon R). The anti-IgE mAb recognize different clusters of epitopes on the Fc region of IgE and could interfere to different degrees with the binding of IgE to mast cells and basophils, but still recognized cell-bound IgE. Analysis of the stoichiometry and affinity binding of 125I anti-IgE mAb Fab' to free IgE have revealed that anti-IgE mAb of one group (51.3) recognized three repetitive determinants on the IgE Fc portion, and another group (95.3) recognized only one determinant. When these stoichiometric studies were performed with cell-bound IgE, it was found that only one of the sites recognized by 51.3 mAb was involved in the Fc epsilon R binding site. On the other hand, the site recognized by 95.3 mAb was not the Fc epsilon R binding site. Such findings establish mAb 51.3 as a useful tool for isolating the IgE peptides involved in the binding site to the receptor.

The role of the Fc epsilon receptor in calcium channel opening in rat basophilic leukemia cells

The role of the Fc epsilon, receptor (Fc epsilon R), isolated from rat basophilic leukemia cells (line RBL-2H3) in antigen induced Ca++ channel opening has been studied by following ion conductance in reconstituted model membranes. Planar bilayers were constructed from lipid vesicles containing the purified Fc epsilon R alone, or together with the cromolyn binding protein (CBP). Changes in conductivity of these bilayers were measured as a monitor for channel activity, following specific aggregation of Fc epsilon R. Antigen-induced, Fc epsilon R mediated channel activity could only be elicited in membranes containing both proteins. This conductance was abrogated upon disaggregating the complexes with a monovalent hapten (epsilon-N-DNP-L-lysine). No channel activity was observed following antigen-induced aggregation of Fc epsilon R if CBP was not present in the bilayer. The single channels recorded were of approximately equal to 2 pS conductance. The open-time values varied significantly with individual experiments and depended on the protein composition of the membrane and the nature of the aggregating agent. These observations strongly indicate that the Fc epsilon R isolated from RBL cells does not form cation (Ca++) channels by itself. Furthermore, in line with earlier reports, the present data suggest that the CBP is responsible for this activity, and that it interacts directly with Fc epsilon R to open channels upon aggregation.

Relationships between epitopes on IgE recognized by defined monoclonal antibodies and by the FC epsilon receptor on basophils

The present study investigated whether the sites on the FC region of the IgE molecule, recognized by different anti-IgE monoclonal antibodies (mAb), are identical to those recognized by the Fc receptor (Fc epsilon R). The anti-IgE mAb recognize different clusters of epitopes on the Fc region of IgE and could interfere to different degrees with the binding of IgE to mast cells and basophils, but still recognized cell-bound IgE. Analysis of the stoichiometry and affinity binding of 125I anti-IgE mAb Fab' to free IgE have revealed that anti-IgE mAb of one group (51.3) recognized three repetitive determinants on the IgE Fc portion, and another group (95.3) recognized only one determinant. When these stoichiometric studies were performed with cell-bound IgE, it was found that only one of the sites recognized by 51.3 mAb was involved in the Fc epsilon R binding site. On the other hand, the site recognized by 95.3 mAb was not the Fc epsilon R binding site. Such findings establish mAb 51.3 as a useful tool for isolating the IgE peptides involved in the binding site to the receptor.

The behavior of the solubilized receptor for immunoglobulin E in polyethylene glycol-detergent solutions: characterization and potential applications

We studied the effect of polyethylene glycol (PEG) on the solubility of the receptor for immunoglobulin E (IgE) in non-ionic detergent extracts of rat basophilic leukemia (RBL) cells. We found that the precipitation patterns of free and IgE-bound receptor were identical but differed from that of unbound IgE. Thus, 85 to 95% of the free receptor and the IgE-receptor complexes precipitated at 13% PEG in the presence of 0.5% Nonidet P-40, whereas 95% of the unbound IgE remained soluble. A similar degree of differentiation between the precipitation of receptor-bound and unbound IgE was found when we used extracts and PEG solutions prepared with several non-ionic and/or neutral detergents. The intact IgE-receptor complex with the full complement of subunits (alpha, beta, gamma) precipitated more efficiently than the IgE-alpha-chain-complex. The presence of phospholipids, which were previously shown to be important for preservation of the association between the receptor subunits, enhanced the efficiency of precipitation of the IgE-receptor complex. The presence of PEG also had an effect on the solubility of cellular phospholipids and some of the detergents, although the effect of PEG on either could not be directly related to its effect on the solubility of the IgE-receptor complex. The radioiodinated receptor for IgE, much like other radioiodinated RBL cell membrane proteins, was soluble (greater than or equal to 95%) at approximately 7% PEG but could be specifically and efficiently precipitated from crude cell extracts, in the presence of 7% PEG upon the addition of anti-receptor immunoglobulins alone. Using mouse anti-dinitrophenyl IgE antibody, we found that unlike unbound antigen (DNP-BGG) or the IgE-receptor complex, the detergent-solubilized DNP-BGG-IgE-receptor complex was insoluble at 7% PEG. Consequently, PEG can be employed in assays to quantitate the soluble receptor, and to immunoprecipitate it specifically and directly. Moreover, the use of PEG can facilitate the distinction between unbound antigen and antigen-IgE-receptor complex as well as between the latter and IgE-receptor complex.

The behavior of the solubilized receptor for immunoglobulin E in polyethylene glycol-detergent solutions: characterization and potential applications

We studied the effect of polyethylene glycol (PEG) on the solubility of the receptor for immunoglobulin E (IgE) in non-ionic detergent extracts of rat basophilic leukemia (RBL) cells. We found that the precipitation patterns of free and IgE-bound receptor were identical but differed from that of unbound IgE. Thus, 85 to 95% of the free receptor and the IgE-receptor complexes precipitated at 13% PEG in the presence of 0.5% Nonidet P-40, whereas 95% of the unbound IgE remained soluble. A similar degree of differentiation between the precipitation of receptor-bound and unbound IgE was found when we used extracts and PEG solutions prepared with several non-ionic and/or neutral detergents. The intact IgE-receptor complex with the full complement of subunits (alpha, beta, gamma) precipitated more efficiently than the IgE-alpha-chain-complex. The presence of phospholipids, which were previously shown to be important for preservation of the association between the receptor subunits, enhanced the efficiency of precipitation of the IgE-receptor complex. The presence of PEG also had an effect on the solubility of cellular phospholipids and some of the detergents, although the effect of PEG on either could not be directly related to its effect on the solubility of the IgE-receptor complex. The radioiodinated receptor for IgE, much like other radioiodinated RBL cell membrane proteins, was soluble (greater than or equal to 95%) at approximately 7% PEG but could be specifically and efficiently precipitated from crude cell extracts, in the presence of 7% PEG upon the addition of anti-receptor immunoglobulins alone. Using mouse anti-dinitrophenyl IgE antibody, we found that unlike unbound antigen (DNP-BGG) or the IgE-receptor complex, the detergent-solubilized DNP-BGG-IgE-receptor complex was insoluble at 7% PEG. Consequently, PEG can be employed in assays to quantitate the soluble receptor, and to immunoprecipitate it specifically and directly. Moreover, the use of PEG can facilitate the distinction between unbound antigen and antigen-IgE-receptor complex as well as between the latter and IgE-receptor complex.

Reconstitution of the receptor for immunoglobulin E into liposomes. Reincorporation of purified receptors

Mast cells and related cells have on their surface receptors that bind immunoglobulin E (IgE) with high affinity and which, when aggregated, trigger exocytosis. We recently demonstrated that when these receptors are solubilized with mild detergents, their subunits dissociate unless an appropriate lipid:detergent ratio is maintained. The conditions required to maintain the receptors' integrity appeared to parallel those previously determined as necessary to obtain adequate incorporation of unpurified IgE-receptor complexes from detergent extracts into liposomes. We now show that purified IgE-receptor complexes having the full complement of subunits become preferentially inserted into liposomes. If the receptor subunits are chemically cross-linked to each other, at least some of such receptors can be incorporated, even though lipid is omitted during their purification. The findings suggest that the IgE-binding alpha subunit of the receptor is anchored to the bilayer by means of one or both of the other subunits.

Enhancement of the response of ageing mouse lymphocytes by in vitro treatment with lecithin

The effect of treatment with phosphatidylcholine (lecithin) has been examined on splenocytes from young (6 months) and aged (greater than 20 months) (C3H/eB X C57BL/6)F1 male mice, by probing their responsiveness to proliferative signals of mitogens and mixed lymphocyte reaction. This study was initiated since old mice have been known to manifest an increased ratio of cholesterol: phospholipids (C/PL) in their plasma membranes. Unlike the case in young mice, enhancement in proliferative responses was demonstrated on cells from the old after incubation with lecithin. This enhancement was achieved using a variety of methods by which lymphocytes were exposed to the lipids, and which were all designed to reduce the C/PL ratio in the plasma membrane. The observed differences in response to lecithin treatment between young and old did not stem from different extents of lipid incorporation, and seems unlikely to be a result of modified binding of the mitogens after treatment with the lipid. The data suggest that the normal functional performance of specific reactions, which decline with age, may be restored artificially at an appropriate age, if other complementary functions have not been damaged.

Use of the airfuge for analysis and preparation of receptors incorporated into liposomes: studies with the receptor for immunoglobulin E

A Beckman Airfuge has been employed for studying the interaction between lipids and the receptor for immunoglobulin E (IgE). For analytic experiments, samples were applied underneath a discontinuous sucrose gradient. After a 30-min centrifugation in a fixed-angle rotor, liposomes floated toward the top of the gradient whereas unincorporated receptor-IgE complexes remained at the bottom of the tube. Liposomes with incorporated receptors were also efficiently separated in the ACR-90 preparative rotor. These methods of "Airfuge flotation" can provide useful adjuncts to more traditional methods for density-gradient centrifugation especially when rapid analysis of small samples is desired.

Phospholipids stabilize the interaction between the alpha and beta subunits of the solubilized receptor for immunoglobulin E

The cell-surface component (alpha) which binds monomeric immunoglobulin E with high affinity is associated with a second polypeptide (beta) in the plasma membrane. The latter component tends to dissociate during purification of the alpha chain from detergent extracts of cells, even at neutral pHs and physiological ionic strengths. We now report that the interaction of alpha and beta can be stabilized by maintaining an appropriate phospholipid to detergent ratio. Under such conditions, other discrete components reproducibly copurify with the alpha and beta chains. These results suggest that the subunits of this membrane protein--or the interaction of it with other constituents in the cell--may be stabilized in ways not observed with ordinary soluble proteins.

Nonpolar lipid methylation-identification of nonpolar methylated products synthesized by rat basophilic leukemia cells, retina and parotid

Incorporation of radioactivity from [3H- or 14C-methyl] methionine into nonpolar lipids had been investigated in rat basophilic leukemia (RBL) cells, retina, and rat parotid gland. These nonpolar methylated lipids were extracted into heptane and characterized by thin-layer chromatography, high performance liquid chromatography, gas chromatography, and mass spectrometry. The major methylated nonpolar lipid product in the RBL cells themselves was ubiquinone-9, which accounted for about 90% of the nonpolar lipid and 20-30% of the total radioactive lipid formed. There was a modest increase in the methylation of nonpolar lipids upon stimulation of the RBL cells with IgE and anti-IgE, but the significance of this change is uncertain. In contrast to whole cells, RBL membrane fractions (incubated with [3H-methyl]-S-adenosylmethionine) incorporated radioactivity primarily into fatty acid methyl esters and not ubiquinone. A third product, 2-(methylthio)-benzothiazole, was formed by RBL cells, retina and minced parotid upon incubation in enriched media. This product was formed enzymatically, apparently by the known enzyme S-thiolmethyltransferase, using the thiol substrate which contaminates these media. Evidence suggest that the enzyme may reside, at least in part, on the surface of the cells.

Correlations between membrane viscosity, serum cholesterol, lymphocyte activation and aging in man

Membrane microviscosity, serum cholesterol and lymphocyte stimulation in man were examined in relation to aging. A direct correlation was found between the mole ratio of cholesterol to phospholipids in the serum and the membrane microviscosity of the peripheral blood lymphocyte membranes, both of which increase progressively with age. The increase in membrane microviscosity with age is also concomitant with the decrease in response of the lymphocytes to concanavalin A stimulation. The data suggest that increase in lymphocyte membrane microviscosity is a prominent factor which may lead to the overt reduction of proliferative responses of lymphocytes with aging.

Viscosity of lymphocyte plasma membrane in aging mice and its possible relation to serum cholesterol

Lymphocyte membrane fluidity was examined in aged mice and characterized as a qualitative and effective change which takes place in the aging process. Fluorescence polarization of diphenylhexatriene-labelled mouse spleen cells is substantially higher in cells from old mice (20--36 months) than young mice (2--7 months). A similar difference was also observed with isolated plasma membranes from spleen cells of old and young mice. The overall estimate is that the lipid microviscosity in the lymphocyte plasma membrane from old mice is about 20% higher than that of young mice. The cholesterol/phospholipid ratio determined for the isolated plasma membrane preparations was 0.68 and 0.9, respectively, which is probably the main cause for the difference in membrane viscosity. An elevated cholesterol/phospholipid ratio was also observed in the blood serum of old mice. It is plausible that the source of excess membrane cholesterol in the old mouse lymphocytes originates in the high serum cholesterol.

On the mode of liposome-cell interactions. Biotin-conjugated lipids as ultrastructural probes

An efficient method for labeling and visualizing phospholipids at the ultrastructural level is described. Biotin was coupled to the amines of appropriate phospholipids via the N-hydroxysuccinimide ester. The biotinylated lipid could be specifically labeled by ferritin-avidin conjugates and detected by transmission electron microscopy. The lipid derivatives were analyzed and evaluated in terms of their resemblance to the original lipid. Although differing in some aspects from the parent lipid molecules, the biotinyl derivatives still retain the basic characteristics of lipids vis-a-vis their orientation and position in the membrane bilayer. The latter property renders the biotinylated lipid qualitatively suitable for tracing the fate of the lipid component(s) of liposomes during their interaction with biological membranes of various cell types. Using this system, we propose that the extent and pattern of the liposome-cell interaction depends, at least in part, on the cell type employed. This observation may be due to intrinsic variations in cell surface structure and properties relative to those of the liposome.

Peturbation of lymphocyte response to concanavalin A by exogenous cholesterol and lecithin

Incubation of lymphocytes with lecithin liposomes enriched with cholesterol, elevated the cholesterol level of the cells relative to phospholipids. Treatment of lymphocytes with pure lecithin liposomes resulted in the converse effect. Both these treatments resulted in suppression of the induction phase of the response to concanavalin A and were practically reversible. It is suggested that these changes induce modulations of the fluidity of the lymphocyte membrane which may also take place in vivo by serum lipoproteins. Based on this study, the possible effects of lipids on lymphocyte activation are discussed.

Degree of exposure of membrane proteins determined by fluorescence quenching

Quaternary salts of 4-picoline are shown to act as efficient quenchers of tryptophan fluorescence in membrane proteins. Fluorescence quenching determinations of sarcoplasmic reticulum membranes from rabbit muscle and of human erythrocyte membranes of different cholesterol to phospholipid mole ratios (C/PL) were carried out with quaternary picolinium salts in phosphate-buffered saline (PBS) and in 2,2,2-trifluorethanol (TFE)-water 2:1 (v/v), where the membrane is presumably completely disintegrated. In both solvent systems, the tryptophan quenching characteristics were typical of heterogenous systems and were analyzed as such. The ratio of the fraction of fluorescence intensity available for quenching with N-methylpicolinium perchlorate in PBS and in 2:1 TFE-water, (formula: see text), was taken as an index for the bulk degree of exposure of the membrane proteins to the aqueous surrounding. This value was found to increase with C/PL which is in line with the notion that increase in lipid microviscosity results in increase of exposure of membrane proteins. Analogous experiments were performed with N-hexyl- and N-benzylpicolinium, which can quench tryptophyl residues in both the aqueous phase and the hydrocarbon-water interface, and with N-hexadecylpicolinium which is dissolved in the membrane lipid layer and acts mostly as a static quencher of tryptophan at the hydrocarbon-water interface. With these quenchers the complementary indices (formula: see text) and (formula: see text), which represent the fraction of the protein mass located in the hydrocarbon-water interface and in the hydrocarbon layer, respectively, could be semiquantitatively resolved.