The 86-kilodalton antigen from Schistosoma mansoni is a heat-shock protein homologous to yeast HSP-90

Towards an understanding of the mechanism of action of praziquantel

Although praziquantel (PZQ) has been used to treat schistosomiasis for over 20 years its mechanism of action remains unknown. We have developed an assay based on the transcriptional response of Schistosoma mansoni PR-1 to heat shock to confirm that while 6-week post-infection (p.i.) schistosomes are sensitive to PZQ, 4-week p.i. schistosomes are not. Further, we have used this assay to demonstrate that in mice this sensitivity develops between days 37 and 40 p.i. When PZQ is linked to the fluorophore BODIPY to aid microscopic visualization, it appears to enter the cells of intact 4 and 6-week p.i. schistosomes as well as mammalian NIH 3T3 cells with ease suggesting that the differential effects of PZQ is not based on cell exclusion. A transcriptomal analysis of gene expression between 4 and 6 weeks p.i. revealed 607 up-regulated candidate genes whose products are potential PZQ targets. A comparison of this gene list with that of genes expressed by PZQ sensitive miracidia reduced this target list to 247 genes, including a number involved in aerobic metabolism and cytosolic calcium regulation. Finally, we also report the effect of an in vitro sub-lethal exposure of PZQ on the transcriptome of S. mansoni PR-1. Annotation of genes differentially regulated by PZQ exposure suggests that schistosomes may undergo a transcriptomic response similar to that observed during oxidative stress.

Microarray based analysis of temperature and oxidative stress induced messenger RNA in Schistosoma mansoni

The body's defense against schistosome infection can take many forms. For example, upon developing acute schistosomiasis, patients often have fever coinciding with larval maturation, migration and early oviposition. As the infection becomes established, the parasite comes under oxidative stress generated by the host immune system. The most common treatment for schistosomiasis is the anti-helminthic drug praziquantel. Its effectiveness, however, is limited due to its inability to kill schistosomes 2-4 weeks post-infection. Clearly there is a need for new anti-schistosomal drugs. We hypothesize that gene products expressed as part of a protective response against heat and/or oxidative stress are potential therapeutic targets for future drug development. Using a 12,166 element oligonucleotide microarray to characterize Schistosoma mansoni genes induced by heat and oxidative stress we found that 1878 S. mansoni elements were significantly induced by heat stress. These included previously reported heat-shock genes expressing homologs of HSP40, HSP70 and HSP86. One thousand and one elements were induced by oxidative stress including those expressing homologs of superoxide dismutase, glutathione peroxidase and aldehyde dehydrogenase. Seventy-two elements were common to both stressors and could potentially be exploited in the development of novel anti-schistosomal therapeutics.

Schistosoma mansoni major egg antigen Smp40: molecular modeling and potential immunoreactivity for anti-pathology vaccine development

The pathogenesis of Schistosoma mansoni infection is largely determined by host T-cell mediated immune responses such as the granulomatous response to tissue deposited eggs and subsequent fibrosis. The major egg antigens have a valuable role in desensitizing the CD4+ Th cells that mediate granuloma formation, which may prevent or ameliorate clinical signs of schistosomiasis.S. mansoni major egg antigen Smp40 was expressed and completely purified. It was found that the expressed Smp40 reacts specifically with anti-Smp40 monoclonal antibody in Western blotting. Three-dimensional structure was elucidated based on the similarity of Smp40 with the small heat shock protein coded in the protein database as 1SHS as a template in the molecular modeling. It was figured out that the C-terminal of the Smp40 protein (residues 130 onward) contains two alpha crystallin domains. The fold consists of eight beta strands sandwiched in two sheets forming Greek key. The purified Smp40 was used for in vitro stimulation of peripheral blood mononuclear cells from patients infected with S. mansoni using phytohemagglutinin mitogen as a positive control. The obtained results showed that there is no statistical difference in interferon-g, interleukin (IL)-4 and IL-13 levels obtained with Smp40 stimulation compared with the control group (P > 0.05 for each). On the other hand, there were significant differences after Smp40 stimulation in IL-5 (P = 0.006) and IL-10 levels (P < 0.001) compared with the control group. Gaining the knowledge by reviewing the literature, it was found that the overall pattern of cytokine profile obtained with Smp40 stimulation is reported to be associated with reduced collagen deposition, decreased fibrosis, and granuloma formation inhibition. This may reflect its future prospect as a leading anti-pathology schistosomal vaccine candidate.

Fungal heat-shock proteins in human disease

Heat-shock proteins (hsps) have been identified as molecular chaperones conserved between microbes and man and grouped by their molecular mass and high degree of amino acid homology. This article reviews the major hsps of Saccharomyces cerevisiae, their interactions with trehalose, the effect of fermentation and the role of the heat-shock factor. Information derived from this model, as well as from Neurospora crassa and Achlya ambisexualis, helps in understanding the importance of hsps in the pathogenic fungi, Candida albicans, Cryptococcus neoformans, Aspergillus spp., Histoplasma capsulatum, Paracoccidioides brasiliensis, Trichophyton rubrum, Phycomyces blakesleeanus, Fusarium oxysporum, Coccidioides immitis and Pneumocystis jiroveci. This has been matched with proteomic and genomic information examining hsp expression in response to noxious stimuli. Fungal hsp90 has been identified as a target for immunotherapy by a genetically recombinant antibody. The concept of combining this antibody fragment with an antifungal drug for treating life-threatening fungal infection and the potential interactions with human and microbial hsp90 and nitric oxide is discussed.

Stage-specific alternative splicing of the heat-shock transcription factor during the life-cycle of Schistosoma mansoni

Stage-specific alternative splicing of the heat-shock transcription factor of Schistosoma mansoni (SmHSF) generates isoforms with structural diversity that may modulate the activity of SmHSF at different life-stages, and thus may regulate the expression of different genes at different developmental stages. RT-PCR, cloning and DNA-sequence analyses showed stage-specific alternative splicing inside the DNA-binding domain (DBD) involving introns I1 and I2, and beyond the DBD involving introns I4a and I7. Retention of introns I2 and I4 would inactivate SmHSF since they contain termination codons. Retention of intron I1 would add 11 amino acids inside the DBD and may change the DNA-binding specificity of SmHSF; intron I7 would add 13 amino acids to the effector region of HSF. Retention of introns was more pronounced in cercariae (larval stage living in water) than in adult worms (parasitic form in mammals). The isoforms were expressed in bacteria, but functional evaluation was not feasible, because only the isoform lacking introns was soluble while isoforms with introns were insoluble. However, stage-specific alternative splicing that changed HSF function in vivo was evidenced in intact cercariae. The cercarial SmHSF mRNA was enriched with introns I2 and I4a that contain termination codons. Therefore, translation of the SmHSF mRNA was impaired, and the SmHSF protein was undetectable. Consequently, the HSP70 gene could not be transcribed, and the HSP70 mRNA was missing. Alternative splicing was observed for short DNA segments (33-45 bp) bound by splice signals, located in the coding region. These are not bona fida exons since they are not flanked by introns. Yet, they are not regular introns since they are often found in mature mRNA. Alternative splicing of these DNA segments caused structural diversity that could modulate the function of the gene product.

Genetically recombinant antibodies: new therapeutics against candidiasis

Historically, the therapy of serious fungal infection has been dominated by monotherapy with the polyene antibiotic amphotericin B. Clinical failures, side effects, the lack of alternatives and the toxicity of this drug have heightened the need to produce alternative therapies, which have included fluconazole, voriconazole and caspofungin. The observation that recovery from disseminated candidiasis was associated with an antibody response to the 47 kDa Candida heat-shock protein (HSP)90 homologue, coupled with the ability to sequence all the antibodies from patients who have recovered from the infection and to re-express the dominant ones as fragments in Escherichia coli, has opened the possibility of immunotherapy. The first recombinant antibody fragment, Mycograb (Neu Tec Pharma plc), against Candida HSP90 is now in clinical trials in patients with disseminated candidiasis in Europe and the US. Laboratory and early clinical data support the concept of synergy between Mycograb and amphotericin B. This should improve outcome and diminish the risk of resistance occurring to either drug, without an increase in toxicity, as this should be minimal in a human antibody fragment representing the natural antibody that a patient produces on recovery.

The Schistosoma mansoni soluble proteome: a comparison across four life-cycle stages

Differential analysis of immune responses to schistosomes has routinely been performed using complex mixtures of soluble proteins from various life-cycle stages, on the assumption that these differed significantly in composition. Proteomic techniques now allow us to characterise and compare such mixtures. The soluble proteins from cercariae, lung-schistosomula, adult worms and eggs of Schistosoma mansoni were separated by high-resolution two-dimensional electrophoresis and the resulting images analysed using appropriate software. A high degree of quantitative and qualitative similarity in spot pattern was revealed across the life-cycle, greatest between adjacent stages. To initiate mapping of these soluble proteomes, the 40 most abundant spots in each preparation, accounting for 21-46% of the total protein, were subjected to peptide fingerprinting by mass spectrometry. On average 55% of the spots were identified, but overall, these comprised only 32 different protein species. With one exception all proteins originated in the cytosol and 24 of the 32 had previously been pinpointed by virtue of their immunoreactivity, including four of the WHO priority vaccine candidates. The similarity in composition between the four preparations means that they are unlikely to discriminate adequately between immune responses to different life-cycle stages and argues strongly for the need to identify true stage-specific marker proteins. Equally, it is difficult to reconcile the abundance and immunogenicity of such cytosolic proteins with their status as vaccine candidates, as it is unlikely they will be accessible to the immune system in an intact parasite.

Recombinant antibodies: a natural partner in combinatorial antifungal therapy

Monotherapy, in the form of amphotericin B or one of its liposomal derivatives, is the usual treatment for invasive fungal infections, due to lack of a safe, effective combination of antifungal drugs. Combination therapy is not necessarily beneficial-there may be mutual antagonism or indifference, increased toxicity or interference with concomitant medication. But the benefits of a well-tolerated, synergistic combination would be great-the enhanced efficacy would improve clinical outcome, reduce the need for prolonged courses of treatment and prevent the emergence of antifungal drug resistance. Antifungal antibodies would be a natural partner in a combinatorial approach to antifungal therapy. Analysis of the antibody response which occurs in patients with invasive candidiasis, being treated with amphotericin B, showed a close correlation between recovery and antibody to the immunodominant heat shock protein 90 (hsp90). The molecular chaperone hsp90 is essential for yeast viability. Mycograb is a human recombinant antibody to hsp90 which shows intrinsic antifungal activity and synergy with amphotericin B both in vitro and in vivo. It is now the subject of a multinational, double-blind, placebo-controlled trial, in patients with culture-confirmed invasive candidiasis on liposomal amphotericin B.

Preclinical assessment of the efficacy of mycograb, a human recombinant antibody against fungal HSP90

Mycograb (NeuTec Pharma plc) is a human genetically recombinant antibody against fungal heat shock protein 90 (HSP90). Antibody to HSP90 is closely associated with recovery in patients with invasive candidiasis who are receiving amphotericin B (AMB). Using in vitro assays developed for efficacy assessment of chemotherapeutic antifungal drugs, Mycograb showed activity against a wide range of yeast species (MICs against Candida albicans [fluconazole [FLC]-sensitive and FLC-resistant strains], Candida krusei, Candida tropicalis, Candida glabrata, and Candida parapsilosis, 128 to 256 microg/ml). Mycograb (4 or 8 microg/ml) showed synergy with AMB, the fractional inhibitory index being 0.09 to 0.31. Synergy was not evident with FLC, except for FLC-sensitive C. albicans. Murine kinetics showed that Mycograb at 2 mg/kg produced a maximum concentration of drug in serum of 4.7 microg/ml, a half-life at alpha phase of 3.75 min, a half-life at beta phase of 2.34 h, and an area under the concentration-time curve from 0 to t h of 155 microg. min/ml. Mycograb (2 mg/kg) alone produced significant improvement in murine candidiasis caused by each species: (i). a reduction (Scheffe's test, P < 0.05) in the mean organ colony count for the FLC-resistant strain of C. albicans (kidney, liver, and spleen), C. krusei (liver and spleen), C. glabrata (liver and spleen), C. tropicalis (kidney), and C. parapsilosis (kidney, liver, and spleen) and (ii). a statistically significant increase in the number of negative biopsy specimens (Fisher's exact test, P < 0.05) for C. glabrata (kidney), C. tropicalis (liver and spleen), and C. parapsilosis (liver). AMB (0.6 mg/kg) alone cleared the C. tropicalis infection but failed to clear infections caused by C. albicans, C. krusei, C. glabrata, or C. parapsilosis. Synergy with AMB, defined as an increase (Fisher's exact test, P < 0.05) in the number of negative biopsy specimens compared with those obtained using AMB alone, occurred with the FLC-resistant strain of C. albicans (kidney), C. krusei (spleen), C. glabrata (spleen), and C. parapsilosis (liver and spleen). Only by combining Mycograb with AMB was complete resolution of infection achieved for C. albicans, C. krusei, and C. glabrata.

Heat shock and stress response of Taenia solium and T. crassiceps (Cestoda)

Heat shock and stress responses are documented for the first time in larval stages of the cestodes Taenia solium and Taenia crassiceps. Radioactive metabolic labelling after in vitro incubation of cysts at 43 degrees C, revealed the induction of heat shock proteins. In T. crassiceps, the major heat shock proteins were 80, 70 and 60 kDa. After prolonged incubation, a set of low molecular weight heat shock proteins (27, 31, 33 and 38 kDa), were also induced. In vitro incubation of cysts at 4 degrees C, induced the synthesis of stress proteins ranging from 31 to 80 kDa, indicating the parasite is also able to respond to cold shock. T. solium cysts exposure to temperature stress also resulted in an increased synthesis of 2 major heat shock proteins of 80 and 70 kDa. Western blots using the excretory-secretory products of T. solium showed that 2 heat shock proteins were recognized by antibodies in the sera of cysticercotic patients: one of 66 kDa and another migrating close to the run front. The T. solium 66 kDa protein was also recognized by specific antibodies directed to a 60 kDa bacterial heat shock protein, suggesting that it belongs to this family of proteins.

The Hsp90 of Candida albicans can confer Hsp90 functions in Saccharomyces cerevisiae: a potential model for the processes that generate immunogenic fragments of this molecular chaperone in C. albicans infections

During infections with a number of important eukaryotic pathogens the Hsp90 molecular chaperone of the pathogen is recognized as an immunodominant antigen by the host immune system. Yeast molecular genetics should allow study of the extent of sequence variation within conserved immunodominant epitopes on pathogen Hsp90s that is compatible with essential Hsp90 functions, as well as the processes that generate antigenic subfragments of these Hsp90s. The Hsp90 of the fungal pathogen Candida albicans was shown in this study to provide both essential and nonessential (pheromone signalling and mammalian steroid receptor activation) Hsp90 functions in Saccharomyces cerevisiae cells. Much of the C. albicans Hsp90 expressed in respiratory S. cerevisiae cells was shown to undergo a partial degradation in vivo, a degradation that closely resembles that of the native Hsp82 (one isoform of the homologous Hsp90) in S. cerevisiae. Allowing for the differences in the length of the charged linker region between the N- and C-terminal domains of C. albicans Hsp90 and S. cerevisiae Hsp82, these two proteins expressed in S. cerevisiae appear to give the same major degradation products. These Hsp90 fragments are similar to the products of incomplete Hsp90 degradation found in C. albicans cultures.

Immune response against heat shock proteins in infectious diseases

Heat shock proteins (hsp) are conserved molecules that play an important role in protein folding and assembly and in translocation of proteins between different compartments. Under stress, hsp synthesis is drastically increased, representing a mechanism essential for cell survival. During infection or inflammation, numerous hsp are overexpressed. Not surprisingly, hsp represent dominant antigens in many infectious and autoimmune diseases that induce strong humoral and cellular immune responses. There is substantial evidence that hsp are dominant immune targets in a number of diseases, to the benefit or detriment of man. Nevertheless, findings also exist which argue against a universal role for hsp as target antigens in disease situations. It is suggested that hsp mainly serve as 'early' targets in the immune response, thus providing support for anti-infectious or autoaggressive immune responses directed against unique pathogen- or disease-associated antigens, respectively.

Role of heat shock proteins in protection from and pathogenesis of infectious diseases

Increased synthesis of heat shock proteins (hsp) occurs in prokaryotic and eukaryotic cells when they are exposed to stress. By increasing their hsp content, cells protect themselves from lethal assaults, primarily because hsp interfere with the uncontrolled protein unfolding that occurs under stress. However, hsp are not produced only by stressed cells; some hsp are synthesized constitutively and perform important housekeeping functions. Accordingly, hsp are involved in the assembly of molecules which play important roles in the immune system. It is not surprising that due to their wide distribution and their homology among different species, hsp represent target antigens of the immune response. Frequent confrontation of the immune system with conserved regions of hsp which are shared by various microbial pathogens can potentiate antimicrobial immunity. However, long-term confrontation of the immune system with hsp antigens which are similar in the host and invaders may convert the immune response against these host antigens and promote autoimmune disease. This review provides an overview of the role of hsp in immunity with a focus on infectious and autoimmune diseases.

The 90-kDa molecular chaperone family: structure, function, and clinical applications. A comprehensive review

The 90-kDa molecular chaperone family (which comprises, among other proteins, the 90-kDa heat-shock protein, hsp90 and the 94-kDa glucose-regulated protein, grp94, major molecular chaperones of the cytosol and of the endoplasmic reticulum, respectively) has become an increasingly active subject of research in the past couple of years. These ubiquitous, well-conserved proteins account for 1-2% of all cellular proteins in most cells. However, their precise function is still far from being elucidated. Their involvement in the aetiology of several autoimmune diseases, in various infections, in recognition of malignant cells, and in antigen-presentation already demonstrates the essential role they likely will play in clinical practice of the next decade. The present review summarizes our current knowledge about the cellular functions, expression, and clinical implications of the 90-kDa molecular chaperone family and some approaches for future research.

During canine leishmaniasis a protein belonging to the 83-kDa heat-shock protein family elicits a strong humoral response

By screening of a Leishmania infantum expression library with the serum from a dog affected with visceral leishmaniasis, a cDNA clone with sequence homology to the Hsp83 gene family was isolated. From analysis of the genomic distribution of the cDNA sequence, it was estimated that the L. infantum genome contains 7 Hsp83 genes tandemly organized. The full-length coding region of the Hsp83 gene located at the 5'-end of the cluster was determined. The deduced amino acid sequence of the L. infantum Hsp83 shows a high level of sequence identity with members of the Hsp83's protein family from other eukaryotic organisms. The complete protein (LiHsp83) and 4 subfragments (LiA1, LiB1, LiC1 and LiD1) were expressed in Escherichia coli as recombinant proteins and used as target antigens in FAST-ELISA assays against a collection of sera from dogs with visceral leishmaniasis. Ninety percent of the sera recognized the recombinant LiHsp83, indicating that L. infantum Hsp83 is a potent immunogen during canine leishmaniasis. Serological analysis of the recombinant subfragments identified the LiB1 subfragment, from amino acid 156 to 283, as the immunodominant region of the protein. This region, which is the less evolutionary conserved region of the protein, was recognized by 88% of the visceral leishmaniasis sera. The results suggest that L. infantum Hsp83 and particular protein subfragments may be useful in serodiagnostic assays for canine leishmaniasis.

Heat shock proteins as immunological carriers and vaccines

HSPs are among the major targets of the immune response to bacterial, fungal and parasitic pathogens. The antigenic nature of HSPs is emphasized by evidence that mammals are capable of recognizing multiple B- and T cell epitopes in these proteins. The powerful immunological features of HSPs have led to their experimental use as immunomodulators and as subunit vaccine candidates. Mycobacterial hsp70 and hsp60 have been found to be excellent immunological carriers of molecules against which an immune response is desired; in the absence of adjuvants, the HSPs can stimulate strong and long-lasting immune responses against molecules which have been covalently attached to the HSPs. When used as subunit vaccines, HSPs derived from a variety of bacterial and fungal pathogens have been found to stimulate protective immunity in animal models. These studies suggest that HSPs might be used as immunomodulators or subunit vaccines against infectious disease in man.

Heat shock response of Trichinella spiralis and T. pseudospiralis

Heat shock proteins (HSPs) were documented for the first time in both somatic extracts and excretory/secretory (ES) products of the infective-stage larvae of Trichinella spiralis and T. pseudospiralis. Larvae recovered from muscles of infected mice were heat shocked at 37, 40, 43 and 45 degrees C in RPMI 1640 medium containing L(-)[35S]methionine. Somatic extracts and ES products of heat-shocked worms were then analysed by SDS-PAGE, autoradiography and laser densitometry. Prominent bands of HSPs were observed at 43 degrees C which is the optimal heat shock temperature. The major HSPs in somatic extracts of T. spiralis were 20, 47, 50, 70, 80 and 86 kDa. When the temperature was increased from 37 to 43 degrees C, the greatest increase in absorbance was observed in HSPs 70 and 86. In vitro translation of mRNA in a nuclease-treated rabbit reticulocyte lysate system showed an increase in the synthesis of the 80 kDa protein. This suggests that the production of HSP 80 is regulated at the transcriptional level. The major HSPs in the ES products were 11, 45, 53 and 64 kDa. In T. pseudospiralis, the major HSPs in the somatic extracts were 20, 26, 31, 50, 53, 70, 80 and 86 kDa, and in the ES products, 11, 35, 37, 41 and 64 kDa.

Induction of protective immunity to schistosomiasis with immunologically cross-reactive Lumbricus molecules

Immunologically cross-reactive molecules of Schistosoma japonicum and Lumbricus terrestris were identified by antibodies derived from human and rodent sera. Pooled IgG from schistosomiasis patients but not uninfected individuals bound multiple antigens of identical molecular weight in both soluble S. japonicum worm antigen preparations (SWAP) and soluble earthworm preparations (SEWP). These antigens had molecular weights corresponding to 18, 40, 62, 64, 74, 97, and > 110 kDa. Three of these antigens of 74, 97 and > 110 kDa were immuno-affinity purified using antibodies derived from schistosomiasis patients' sera. Vaccination of mice with SEWP produced murine antibodies which bound parasite molecules of 40, 74, 97, and > 110 kDa and induced 36% protection from S. japonicum infection (P < 0.05). Antibody production to S. japonicum paramyosin, a molecule previously shown to induce protection from schistosome infection, was prominently expressed in the protected murine immune sera. The study shows that Lumbricus sp. represent a potential source for paramyosin and other candidate vaccine molecules for schistosomiasis.

Hsp70 in parasites: as an inducible protective protein and as an antigen

The heat shock (HS) response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stresses. It has been demonstrated that heat shock proteins (HSP) play major roles in many cellular processes, and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology, from cancer research to interaction between host and parasites. This review deals with the hsp70 gene family and with its protein product, hsp70, as an antigen when pathogens infect humans. Members of HSP have been shown to be major antigens of many pathogenic organisms when they experience a major temperature shift upwards at the onset of infection and become targets for host B and T cells.

Dinucleotide biases in the platyhelminth Schistosoma mansoni

The analysis of dinucleotide biases in coding and flanking regions, introns, rDNA and repetitive sequences, in the flatworm Schistosoma mansoni is reported. Except for rDNA, all regions display CpG avoidance and TpG plus CpA excess, which might be evidence of the presence of 5mC. The distribution and hierarchies of dinucleotides differ from the data published for invertebrate and vertebrate coding sequences.

Immunogenicity and antigenicity of a Plasmodium falciparum protein fraction (90-110 kDa) able to protect squirrel monkeys against asexual blood stages

A monkey vaccination trial using a Plasmodium falciparum protein fraction containing antigens of 90-110 kDa is reported. The fraction was obtained by electroelution from preparative polyacrylamide gels. Three monkeys out of five resisted a heavy challenge dose of highly virulent parasites. Using specific antisera, several components of the fraction were identified, namely heat shock protein 90 (hsp90), Ag44/RhopH3, ABRA, 96tR/GBP130 and Pf96 protease. The fraction did not contain KAHRP, nor the SERP antigen. The antibody response of the monkeys was studied on these individual antigens purified by preparative immunoprecipitation. Surprisingly, hsp90 was found in the immunoprecipitates obtained with SERP antisera. Interestingly, the response to hsp90 correlated with protection, high antibody titres being found only in the protected monkeys. In contrast, no correlation with protection could be found for the response to the other antigens.

The biology of the heat shock response in parasites

The heat shock response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stress. It has been shown that heat shock proteins play major roles in many cellular processes and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology and from cancer research to interactions between host and parasite. In this review, Bruno Maresca and Luisella Carratu deal with some of the unique characteristics of the heat shock response in parasitic organisms.

Alternative patterns of MHC-restricted antibody responsiveness following intraperitoneal immunization of inbred mice with different preparations of an 86 kilodalton antigen of Schistosoma mansoni

The investigation of MHC restricted antibody responses to an 86 kDa antigen (p86) during chronic Schistosoma mansoni infection has been extended to immunization with this antigen. In the absence of adjuvant, a similar pattern of responsiveness by mice expressing H-2k and H-2d but not H-2b was observed following immunization with unpurified adult worm homogenate. Adjuvant selectively abrogated the capacity of H-2d mice to respond and this was also the case when purified p86 with adjuvant was injected. Immunization with purified subfragments of p86 again demonstrated MHC restriction in the capacity to immunoprecipitate p86 in vitro translation product, the pattern varying according to the fragment used. Western blot analysis showed that in some, but not all instances of apparent 'non-responsiveness' characterized by immunoprecipitation, antibody specificities capable of recognizing p86 epitopes on the nitrocellulose bound p86 were, indeed, present. Thus the fine specificity as well as the absolute capacity to respond is influenced by both the MHC haplotype of the host and the nature of the immunizing antigen.

MHC-restriction of antibody responses to an 86 kilodalton antigen of Schistosoma mansoni

The previously observed MHC-restriction of the antibody response to an 86kDa S. mansoni antigen has been investigated in more detail. The I-A locus of the H-2 complex has been implicated as conferring responder or non-responder status on mice expressing the k and b alleles respectively. Inheritance of responsiveness was dominant over non-responsiveness. An additional level of complexity was observed in the p86 antibody responder status of individuals within a responding inbred strain. This could not be accounted for directly by the level of patent infection, but showed an inverse correlation with the level of egg output in H-2k mice. Differential antibody responsiveness to other antigens, between individuals of the same strain, occurred independently of the differential responsiveness to p86.

Autoimmunity, microbial immunity and the immunological homunculus

Clonal deletion and anergy are believed by many immunologists to be the fundamental mechanisms responsible for self tolerance. Nevertheless, as Irun Cohen and Douglas Young point out, such notions of nonreactivity cannot explain certain key features of immune behaviour: the immunological dominance of microbial antigens that mimic self, the uniformity of autoimmune diseases and the prevalence of natural autoimmunity among the healthy. The theory of the immunological homunculus is presented here as a unifying principle.

The role of a stress-response protein in Salmonella typhimurium virulence

We recently described the use of selective transposon mutagenesis to generate a series of avirulent mutants of a pathogenic strain of Salmonella typhimurium. Cloning and sequencing of the insertion sites from two of these mutants reveals that both have identical locations within an open reading frame that is highly homologous to a gene, htrA, encoding a heat-shock protein in Escherichia coli. DNA sequence analysis of S. typhimurium htrA reveals the presence of a gene capable of encoding a protein with a calculated Mr of 49316 that has 88.7% protein:protein homology with its E. coli counterpart. In E. coli, lesions in this gene, also known as degP, reduce proteolytic degradation of aberrant periplasmic proteins. Characteristics of the S. typhimurium htrA mutants, 046 and 014, in vivo and in vitro suggested that they are avirulent because of impaired ability to survive and/or replicate in host tissues. In vitro, the S. typhimurium htrA mutants 046 and 014 are not temperature-sensitive but were found to be more susceptible to oxidative stress than the parent, suggesting that they may be less able to withstand oxidative killing within macrophages.