Persistent Staphylococcus aureus isolates from two independent cases of bacteremia display increased bacterial fitness and novel immune evasion phenotypes.

Staphylococcus aureus bacteremia cases are complicated by bacterial persistence and treatment failure despite the confirmed in vitro susceptibility of the infecting strain to administered antibiotics. A high incidence of methicillin-resistant S. aureus (MRSA) bacteremia cases are classified as persistent and are associated with poorer patient outcomes. It is still unclear how S. aureus evades the host immune system and resists antibiotic treatment for the prolonged duration of a persistent infection. In this study, the genetic changes and associated phenotypic traits specific to S. aureus persistent bacteremia were identified by comparing temporally dispersed isolates from persistent infections (persistent isolates) originating from two independent persistent S. aureus bacteremia cases with the initial infection isolates and with three resolved S. aureus bacteremia isolates from the same genetic background. Several novel traits were associated specifically with both independent sets of persistent S. aureus isolates compared to both the initial isolates and the isolates from resolved infections (resolved isolates). These traits included (i) increased growth under nutrient-poor conditions; (ii) increased tolerance of iron toxicity; (iii) higher expression of cell surface proteins involved in immune evasion and stress responses; and (iv) attenuated virulence in a Galleria mellonella larva infection model that was not associated with small-colony variation or metabolic dormancy such as had been seen previously. Whole-genome sequence analysis identified different single nucleotide mutations within the mprF genes of all the isolates with the adaptive persistence traits from both independent cases. Overall, our data indicate a novel role for MprF function during development of S. aureus persistence by increasing bacterial fitness and immune evasion.

The immersion foot syndrome. 1946.

1. Prolonged exposure of the extremities to cold insufficient to cause tissue freezing produces a well-defined syndrome. 'Immersion foot' is one of the descriptive but inaccurate terms applied to this syndrome. The clinical features, aetiology, pathology, prevention, and treatment of immersion foot are considered in detail. A discussion on pathogenesis is also included. 2. In the natural history of a typical case of immersion foot there are four stages: the period of exposure and the pre-hyperaemic, hyperaemic, and post-hyperaemic stages. 3. During exposure and immediately after rescue the feet are cold, numb, swollen, and pulseless. Intense vasoconstriction sufficient to arrest blood-flow is believed to be the predominant factor during this phase. 4. This is followed by a period of intense hyperaemia, increased swelling, and severe pain. Hyperaemia is due to the release in chilled and ischaemic tissues of relatively stable vasodilator metabolites; pain may be the result of relative anoxia of sensory nerve-endings. 5. Within 7-10 days of rescue the intense hyperaemia and swelling subside and pain diminishes in intensity. A lesser degree of hyperaemia may persist for several weeks. Objective disturbances of sensation and sweating and muscular atrophy and paralysis now become apparent. These findings are correlated with damage to the peripheral nerves. 6. After several weeks the feet become cold-sensitive; when exposed to low temperature they cool abnormally and may remain cold for several hours. Hyperhidrosis frequently accompanies this cold-sensitivity. The factors responsible for these phenomena are incompletely understood; several possible explanations are considered. 7. Severe cases may develop blisters and gangrene. The latter is usually superficial and massive loss of tissue is rare. 8. The hands may be affected but seldom as severely as the feet. The essential features of immersion hand are the same as those of immersion foot. 9. Prognosis depends upon severity. The extent of anaesthesia at 7-10 days has been found a useful guide to the latter, and has formed a basis of a method of classification. 10. Rapid warming of chilled tissues is condemned. Cold therapy is of value for the relief of pain in the hyperaemic stage, but should not be used in the pre-hyperaemic stage. Sympathectomy and other measures designed to increase the peripheral circulation should not be employed immediately after rescue, but may have a place in the treatment of the later cold-sensitive state. This paper records the results of observations made during 1941 and 1942. Delay in publication has been necessary because of war-time difficulties of maintaining contact between authors. In this respect we have received much help from Surgeon Rear-Admiral J. W. McNee. We wish to thank Professors R. S. Aitken and J. R. Learmonth for much helpful advice during the preparation of the paper. The charts have been prepared by the technical staff of the Wilkie Surgical Research Laboratory, University of Edinburgh. During the period of the study, one of us (R. L. R.) was in receipt of a personal grant from the Medical Research Council.

Reactions of dimethylsulfoxide reductase in the presence of dimethyl sulfide and the structure of the dimethyl sulfide-modified enzyme.

The bis-molybdopterin enzyme dimethylsulfoxide reductase (DMSOR) from Rhodobacter capsulatus catalyzes the conversion of dimethyl sulfoxide (DMSO) to dimethyl sulfide (DMS), reversibly, in the presence of suitable e(-)-donors or e(-)-acceptors. The catalytically significant intermediate formed by reaction of DMSOR with DMS ('the DMS species') and a damaged enzyme form derived by reaction of the latter with O(2) (DMS-modified enzyme, DMSOR(mod)D) have been investigated. Evidence is presented that Mo in the DMS species is not, as widely assumed, Mo(IV). Formation of the DMS species is reversed on removing DMS or by addition of an excess of DMSO. Equilibrium constants for the competing reactions of DMS and DMSO with the oxidized enzyme (K(d) = 0.07 +/- 0.01 and 21 +/- 5 mM, respectively) that control these processes indicate formation of the DMS species occurs at a redox potential that is 80 mV higher than that required, according to the literature, for reduction of Mo(VI) to Mo(IV) in the free enzyme. Specificity studies show that with dimethyl selenide, DMSOR yields a species analogous to the DMS species but with the 550 nm peak blue-shifted by 27 nm. It is concluded from published redox potential data that this band is due to metal-to-ligand charge transfer from Mo(V) to the chalcogenide. Since the DMS species gives no EPR signal in the normal or parallel mode, a free radical is presumed to be in close proximity to the metal, most likely on the S. The species is thus formulated as Mo(V)-O-S(*)Me(2). Existing X-ray crystallographic and Raman data are consistent with this structure. Furthermore, 1e(-) oxidation of the DMS species with phenazine ethosulfate yields a Mo(V) form without an -OH ligand, since its EPR signal shows no proton splittings. This form presumably arises via dissociation of DMSO. The structure of DMSOR(mod)D has been determined by X-ray crystallography. All four thiolate ligands and Ogamma of serine-147 remain coordinated to Mo, but there are no terminal oxygen ligands and Mo is Mo(VI). Thus, it is a dead-end species, neither oxo group acceptance nor e(-)-donation being possible. O(2)-dependent formation of DMSOR(mod)D represents noncatalytic breakdown of the DMS species by a pathway alternative to that in turnover, with oxidation to Mo(VI) presumably preceding product release. Steps in the forward and backward catalytic cycles are discussed in relation to earlier stopped-flow data. The finding that in the back-assay the Mo(IV) state may at least in part be by-passed via two successive 1e(-) reactions of the DMS species with the e(-)-acceptor, may have implications in relation to the existence of separate molybdopterin enzymes catalyzing DMSO reduction and DMS oxidation, respectively.

Vanadium complexes of the N(CH2CH2S)3(3-) and O(CH2CH2S)2(2-) ligands with coligands relevant to nitrogen fixation processes.

Vanadium(III) and vanadium(V) complexes derived from the tris(2-thiolatoethyl)amine ligand [(NS3)3-] and the bis(2-thiolatoethyl)ether ligand [(OS2)2-] have been synthesized with the aim of investigating the potential of these vanadium sites to bind dinitrogen and activate its reduction. Evidence is presented for the transient existence of (V(NS3)(N2)V(NS3), and a series of mononuclear complexes containing hydrazine, hydrazide, imide, ammine, organic cyanide, and isocyanide ligands has been prepared and the chemistry of these complexes investigated. [V(NS3)O] (1) reacts with an excess of N2H4 to give, probably via the intermediates (V(NS3)(NNH2) (2a) and (V(NS3)(N2)V(NS3) (3), the V(III) adduct [V(NS3)(N2H4)] (4). If 1 is treated with 0.5 mol of N2H4, 0.5 mol of N2 is evolved and green, insoluble [(V(NS3))n] (5) results. Compound 4 is converted by disproportionation to [V(NS3)(NH3)] (6), but 4 does not act as a catalyst for disproportionation of N2H4 nor does it act as a catalyst for its reduction by Zn/HOC6H3Pri2-2,6. Compound 1 reacts with NR1(2)NR2(2) (R1 = H or SiMe3; R2(2) = Me2, MePh, or HPh) to give the hydrazide complexes [V(NS3)(NNR2(2)] (R2(2) = Me2, 2b; R2(2) = MePh, 2c; R2(2) = HPh, 2d), which are not protonated by anhydrous HBr nor are they reduced by Zn/HOC6H3Pri2-2,6. Compound 2b can also be prepared by reaction of [V(NNMe2)(dipp)3] (dipp = OC6H3Pri2-2,6) with NS3H3. N2H4 is displaced quantitatively from 4 by anions to give the salts [NR3(4)][V(NS3)X] (X = Cl, R3 = Et, 7a; X = Cl, R3 = Ph, 7b; X = Br, R3 = Et, 7c; X = N3, R3 = Bu(n), 7d; X = N3, R3 = Et, 7e; X = CN, R3 = Et, 7f). Compound 6 loses NH3 thermally to give 5, which can also be prepared from [VCl3(THF)3] and NS3H3/LiBun. Displacement of NH3 from 6 by ligands L gives the adducts [V(NS3)(L)] (L = MeCN, nu CN 2264 cm-1, 8a; L = ButNC, nu NC 2173 cm-1, 8b; L = C6H11NC, nu NC 2173 cm-1, 8c). Reaction of 4 with N3SiMe3 gives [V(NS3)(NSiMe3)] (9), which is converted to [V(NS3)(NH)] (10) by hydrolysis and to [V(NS3)(NCPh3)] (11) by reaction with ClCPh3. Compound 10 is converted into 1 by [NMe4]OH and to [V(NS3)NLi(THF)2] (12) by LiNPri in THF. A further range of imido complexes [V(NS3)(NR4)] (R4 = C6H4Y-4 where Y = H (13a), OMe (13b), Me (13c), Cl (13d), Br (13e), NO2 (13f); R4 = C6H4Y-3, where Y = OMe (13g); Cl (13h); R4 = C6H3Y2-3,4, where Y = Me (13i); Cl (13j); R4 = C6H11 (13k)) has been prepared by reaction of 1 with R4NCO. The precursor complex [V(OS2)O(dipp)] (14) [OS2(2-) = O(CH2CH2S)2(2-)] has been prepared from [VO(OPri)3], Hdipp, and OS2H2. It reacts with NH2NMe2 to give [V(OS2)(NNMe2)(dipp)] (15) and with N3SiMe3 to give [V(OS2)(NSiMe3)(dipp)] (16). A second oxide precursor, formulated as [V(OS2)1.5O] (17), has also been obtained, and it reacts with SiMe3NHNMe2 to give [V(OS2)(NNMe2)(OSiMe3)] (18). The X-ray crystal structures of the complexes 2b, 2c, 4, 6, 7a, 8a, 9, 10, 13d, 14, 15, 16, and 18 have been determined, and the 51V NMR and other spectroscopic parameters of the complexes are discussed in terms of electronic effects.

Immunogenicity of Plasmodium falciparum circumsporozoite protein multiple antigen peptide vaccine formulated with different adjuvants.

Only low antibody levels were obtained from vaccinating human volunteers with single-chain peptide from the Plasmodium falciparum circumsporozoite protein (PfCSP). This resulted in modest protection against sporozoite challenge. In addition, HLA restriction limits the probability of synthesis of a vaccine effective for a diverse population. We report immunization studies with a multiple antigen peptide (MAP) system consisting of multiple copies of a B-cell epitope from the central repeat region of the PfCSP in combination with a universal T-cell epitope, the P2P30 portion of tetanus toxin. This MAP4(NANP)6P2P30 vaccine was highly immunogenic in four different strains of mice when used with various safe and nontoxic adjuvants. When this MAP vaccine was encapsulated in liposomes with lipid A and adsorbed to aluminium hydroxide and given three times at 4-week intervals, the resultant antibody prevented 100% of sporozoites from invading and developing into liver stage infection. This high degree of immunogenicity of MAP4(NANP)6P2P30 vaccine formulated in liposomes, lipid A and aluminum hydroxide provides the foundation for consideration of human trials with this formulation.

Liposomes containing lipid A serve as an adjuvant for induction of antibody and cytotoxic T-cell responses against RTS,S malaria antigen.

Encapsulation of soluble protein antigens in liposomes was previously shown to result in processing of antigen via the major histocompatibility complex class I pathway, as evidenced by costaining of the trans-Golgi region of murine bone marrow-derived macrophages (BMs) by fluorophore-labeled liposomal antigen and by a trans-Golgi-specific fluorescent lipid. Evidence is presented here that free or liposome-encapsulated RTS,S, a particulate malaria antigen consisting of hepatitis B particles coexpressed with epitopes from the Plasmodium falciparum circumsporozoite protein, also was localized in the trans-Golgi after incubation with BMs, suggesting processing by the class I pathway. An in vivo cytotoxic T-lymphocyte (CTL) response was detected, however, only after immunization with RTS,S encapsulated in liposomes containing lipid A and not after immunization with free RTS,S or with RTS,S encapsulated in liposomes lacking lipid A. Therefore, intracellular delivery of antigen containing CTL epitopes to the Golgi of BMs does not necessarily result in a CTL response in vivo unless an additional adjuvant, such as liposomes containing lipid A, is utilized. Encapsulation of RTS,S in liposomes containing monophosphoryl lipid A (MPL) resulted in a dose-dependent enhancement of the NANP-specific immunoglobulin G (IgG) antibody response compared to that of free RTS,S. The IgG1 and IgG2a subclasses predominated after immunization with RTS,S encapsulated in liposomes containing MPL. These results demonstrate that encapsulation of a lipid-containing particulate antigen, such as RTS, S, in liposomes containing lipid A can enhance both humoral and cellular immune responses.

Immunization against the murine malaria parasite Plasmodium yoelii using a recombinant protein with adjuvants developed for clinical use.

Mice vaccinated with a recombinant protein containing the two EGF-like modules of Plasmodium yoelii merozoite surface protein-1 in liposomes or combined with the formulations SBAS2.1 and SBAS2, were protected against a lethal malaria infection. The protection achieved with these adjuvants developed for clinical use was as good as or better than that achieved with Freund's adjuvant. A parasite-specific response was needed for protection. Analysis of the immunoglobulin sub-class response showed that MSP-1-specific IgG1, and to a lesser extent IgG2a and IgG2b, were induced, suggesting that these antibodies were important for protection. Mice passively immunized with serum or purified IgG from vaccinated mice had delayed onset of parasitemia and were able to control the infection.

Selection of an adjuvant for vaccination with the malaria antigen, MSA-2.

Various formulations of the Plasmodium falciparum merozoite surface antigen, MSA-2, were made and tested in animals in order to select one for use in human vaccine trials. Recombinant constructs representing both major allelic forms of MSA-2 were formulated with a range of adjuvants and used to immunize rabbits, mice and sheep. After immunization, antibody responses obtained with the most potent adjuvants were at least tenfold greater than responses obtained with the least potent adjuvant Alhydrogel, which was used as the reference standard, although its lower potency indicated against its further use in clinical trials. Based on broadly similar results obtained with the three animal species, several adjuvants, including the water-in-oil adjuvant Montanide ISA 720, the oil-in-water adjuvant SAF-1, and liposomes containing lipid A formulated with Alhydrogel were demonstrated to be potent and potentially suitable for the clinical evaluation of MSA-2 as a candidate malaria vaccine antigen. Of these, ISA 720 was selected for further trial.

Liposomal subunit vaccines: effects of lipid A and aluminum hydroxide on immunogenicity.

Protein and peptide antigens frequently are only slightly immunogenic when utilized alone in vaccines. Formulation of these antigens in a carrier vehicle, particularly when an adjuvant is included, often results in markedly enhanced immune responses. Encapsulation of peptide and protein antigens in liposomes generally results in a relatively slight enhancement of antibody production compared with that observed with the antigen alone. However, when lipid A is included in the liposomes, immunogenicity is markedly increased compared both with antigen alone and with antigen encapsulated in liposomes lacking lipid A. The enhancement of the immune response caused by lipid A is dependent on the liposomal lipid A dose. Aluminum salts, such as aluminum hydroxide and aluminum phosphate, act as adjuvants for some antigens and are used in a variety of human vaccines. When liposomes containing encapsulated protein or peptide antigens were adsorbed with aluminum hydroxide, an enhancement of the antibody response was observed with some antigens, whereas with other antigens the presence of aluminum hydroxide either had no effect or resulted in a diminished antibody response. Immunogenicity of protein and peptide antigens can be enhanced by formulation in liposomes containing lipid A and, depending on the antigen, can be enhanced further by adsorption of the liposomal antigen formulation with aluminum salts.

Immunization of Aotus nancymai with recombinant C terminus of Plasmodium falciparum merozoite surface protein 1 in liposomes and alum adjuvant does not induce protection against a challenge infection.

Merozoite surface protein 1 (MSP-1) of Plasmodium falciparum is an antimalarial vaccine candidate. The highly conserved 19-kDa C-terminal processing fragment of MSP-1 (MSP-1(19)) is of particular interest since it contains epitopes recognized by monoclonal antibodies which inhibit the invasion of erythrocytes in vitro. The presence of naturally acquired anti-MSP-1(19) antibodies in individuals exposed to malaria has been correlated with reduced morbidity, and immunization with an equivalent recombinant P. yoelii antigen induces substantial protection against this parasite in mice. We have expressed P. falciparum MSP-1(19) in Escherichia coli as a correctly folded protein and immunized Aotus nancymai monkeys by using the protein incorporated into liposomes and adsorbed to alum. After vaccination, the sera from these animals contained anti-MSP-1(19) antibodies, some of which competed for binding to MSP-1(19) with monoclonal antibodies that inhibit parasite invasion of erythrocytes in vitro. However, after challenge with either a homologous or a heterologous strain of parasite, all animals became parasitemic and required treatment. The immunization did not induce protection in this animal model.

Safety, immunogenicity, and efficacy of Plasmodium falciparum repeatless circumsporozoite protein vaccine encapsulated in liposomes.

Seventeen malaria-naive volunteers received a recombinant Plasmodium falciparum vaccine (RLF) containing the carboxy- and the amino-terminal of the circumsporozoite protein (CSP) antigen without the central tetrapeptide repeats. The vaccine was formulated in liposomes with either a low or high dose of 3-deacylated monophosphoryl lipid A (MPL) and administered with alum by intramuscular injection. Both formulations were well tolerated and immunogenic. MPL increased sporozoite antibody titers measured by ELISA, Western blot, and immunofluorescence assay. One high-dose MPL vaccine formulation recipient developed a CSP-specific cytotoxic T lymphocyte response. After homologous sporozoite challenge, immunized volunteers developed patent malaria. There was no correlation between prepatent period and antibody titers to the amino- or carboxy-terminal. The absence of delay in patency argues against inclusion of the amino-terminal in future vaccines. A significant cytotoxic T lymphocyte response may have been suppressed by the inclusion of alum as an adjuvant.

Evidence favoring molybdenum-carbon bond formation in xanthine oxidase action: 17Q- and 13C-ENDOR and kinetic studies.

The reaction mechanism of the molybdoenzyme xanthine oxidase has been further investigated by 13C and 17O ENDOR of molybdenum(V) species and by kinetic studies of exchange of oxygen isotopes. Three EPR signal-giving species were studied: (i) Very Rapid, a transient intermediate in substrate turnover, (ii) Inhibited, the product of an inhibitory side reaction with aldehyde substrates, and (iii) Alloxanthine, a species formed by reaction of reduced enzyme with the inhibitor, alloxanthine. The Very Rapid signal was developed either with [8-13C]xanthine or with 2-oxo-6-methylpurine using enzyme equilibrated with [17O]H2O. The Inhibited signal was developed with 2H13C2HO and the Alloxanthine signal by using [17O]H2O. Estimates of Mo-C distances were made, from the anisotropic components of the 13C-couplings, by corrected dipolar coupling calculations and by back-calculation from assumed possible structures. Estimated distances in the Inhibited and Very Rapid species were about 1.9 and less than 2.4 A, respectively. A Mo-C bond in the Inhibited species is very strongly suggested, presumably associated with side-on bonding to molybdenum of the carbonyl of the aldehyde substrate. For the Very Rapid species, a Mo-C bond is highly likely. Coupling from a strongly coupled 17O, not in the form of an oxo group, and no coupling from other oxygens was detected in the Very Rapid species. No coupled oxygens were detected in the Alloxanthine species. That the coupled oxygen of the Very Rapid species is the one that appears in the product uric acid molecule was confirmed by new kinetic data. It is concluded that this oxygen of the Very Rapid species does not, as frequently assumed, originate from the oxo group of the oxidized enzyme. A new turnover mechanism is proposed, not involving direct participation of the oxo ligand group, and based on that of Coucouvanis et al. [Coucouvanis, D., Toupadakis, A., Lane, J. D., Koo, S. M., Kim, C. G., Hadjikyriacou, A. (1991) J. Am. Chem. Soc. 113, 5271-5282]. It involves formal addition of the elements of the substrate (e.g., xanthine) across the Mo = S double bond, to give a Mo(VI) species. This is followed by attack of a "buried" water molecule (in the vicinity of molybdenum and perhaps a ligand of it) on the bound substrate carbon, to give an intermediate that on intramolecular one-electron oxidation gives the Very Rapid species. The latter, in keeping with the 13C, 17O, and 33S couplings, is presumed to have the 8-CO group of the uric acid product molecule bonded side-on to molybdenum, with the sulfido molybdenum ligand retained, as in the oxidized enzyme.

Murine IgG subclass antibodies to antigens incorporated in liposomes containing lipid A.

The IgG subclass responses to antigens incorporated in liposomes containing lipid A were investigated using a synthetic malarial antigen (SPf66) and cholera toxin (CT). The antigen-specific IgG subclass response was determined in BALB/c mice immunized with either: (a) SPf66 encapsulated in liposomes containing lipid A, (b) CT bound to the surface of liposomes containing lipid A, or (c) both encapsulated SPf66 and surface-bound CT in the same liposomes. In each case the antibodies to SPf66, CT and lipid A demonstrated an IgG2a predominance. Liposomes containing lipid A not only increased the magnitude of the antibody response to liposomal antigens but elicited predominantly IgG2a subclass antibodies as well.

Liposomes as carriers for vaccines.

A liposome vaccine formulation that has been successfully used in both animal immunization studies and clinical trials is described. Issues concerning the choice of components for the liposomal vaccine formulation are discussed, especially with respect to the lipid components and the adjuvant. A procedure is described for manufacturing liposomal vaccines using Good Manufacturing Practices as promulgated by the U.S. Food and Drug Administration. Quality control testing for clinical use is described, with particular emphasis on aspects relevant to liposomes. Utilization issues are discussed, including injection volumes, antigen and adjuvant doses, and routes of administration.

Predicting hospital mortality in patients with acute myocardial infarction.

BACKGROUND Patients who have a myocardial infarction are a heterogeneous group. If those at risk for early mortality could be readily identified, it would provide a more solid basis for management decisions. Although past research has explored factors associated with mortality, findings are inconsistent. Variables have also been combined into prognostic indices, but these tools have yet to be evaluated adequately. OBJECTIVES To determine factors predictive of hospital mortality in patients with acute myocardial infarction, and to examine the usefulness of two severity-of-illness indices. METHODS The medical records of 392 patients diagnosed with acute myocardial infarction who had undergone coronary angiography during 1989 at a university medical center were reviewed. RESULTS Overall mortality was 9.4% (n = 37). Logistic regression analysis demonstrated that history of myocardial infarction, cardiogenic shock, age, left ventricular ejection fraction, and the number of occluded coronary vessels were significantly associated with hospital mortality in patients with acute myocardial infarction. The two severity-of-illness indices were significant predictors of mortality, although sensitivity, specificity, and predictive values varied. A formula for determining the probability of mortality, based on logistic regression analysis, is also presented. CONCLUSIONS Five factors were found to predict hospital mortality. The two severity-of-illness indices were moderately useful in predicting mortality. Unlike previous indices that did not incorporate currently available diagnostic data, the new formula included data from coronary angiography and nuclear scans. Although this formula requires validation on independent samples of patients with myocardial infarction, the findings of this study advance clinicians' ability to predict patient outcome.

Electron-paramagnetic-resonance and magnetic-circular-dichroism studies of the binding of cyanide and thiols to the thiols to the iron-molybdenum cofactor from Klebsiella pneumoniae nitrogenase.

FeMoco, a low-M(r) metal cluster of probable composition Fe7MoS9 complexed with homocitrate, has been extracted with N-methylformamide from the MoFe protein of the nitrogenase enzyme from Klebsiella pneumoniae. The binding of cyanide and thiols to the FeMoco cluster in its paramagnetic S = 3/2 oxidation level has been studied by low-temperature e.p.r. and magnetic-circular-dichroism (m.c.d.) spectroscopies. Cyanide binds to isolated FeMoco at more than one site, and causes changes in the g values form g = 4.6, 3.2, 2.0 to g = 4.29, 3.82, 2.02 E.p.r. competition studies indicate that one cyanide can be displaced by thiolate from one type of site. The form of the low-temperature m.c.d. spectrum is little changed by ligand binding, thus the basic cluster structure remains intact. However, when benzenethiol is bound, a new intense band (lambda 387 nm) is observed, indicating the generation of an increased ligand-to-cluster charge-transfer interaction.

Induction of cytolytic and antibody responses using Plasmodium falciparum repeatless circumsporozoite protein encapsulated in liposomes.

Plasmodium circumsporozoite (CS) protein-induced antibody and T-cell responses are considered to be important in protective immunity. Since the key repeat determinant of the CS protein may actually restrict the recognition of other potential T- and B-cell sites, a modified Plasmodium falciparum CS protein lacking the central repeat region, RLF, was expressed in Escherichia coli. On purification, RLF was encapsulated into liposomes [L(RLF)] and used for the in vivo induction of cytolytic T lymphocytes (CTL) and antibodies. Immunization of B10.Br (H-2k) mice with L(RLF), but not with RLF, induced CD8+ CTL specific for the P. falciparum CS protein CTL epitope, amino acid residues 368-390. Anti-L(RLF) serum reacted with antigens on intact sporozoites and inhibited sporozoite invasion of hepatoma cells. Antibody specificity studies in New Zealand White rabbits revealed new B-cell sites localized in amino acid residues 84-94, 91-99, 97-106 and 367-375. Although the mechanisms by which liposomes enhance cellular and humoral immune responses remain unknown, liposome-formulated vaccines have been well tolerated in humans; hence, their use in vaccines, when efficacy depends on antibody and CTL responses, may be broadly applicable.