The immunologic abnormalities in patients with paroxysmal nocturnal hemoglobinuria are associated with disease progression

OBJECTIVES

To suggest the presence of a hyperimmune state in patients, and indicate that immune system attack on glycosylphosphatidylinositol (+) (GPI+) cells while escaping GPI- cell immunity.

METHODS

We retrospective the immune cell subtypes in peripheral blood from 25 patients visiting Tianjin Medical University General Hospital, Tianjin, China, with classical paroxysmal nocturnal hemoglobinuria (PNH) and 50 healthy controls.

RESULTS

The total CD3+ and CD3+CD8+ cell levels were higher in patients with PNH. The CD3+ cells are positively, correlated with lactate dehydrogenase (LDH; r=0.5453, p=0.0040), indirect bilirubin (r=0.4260, p=0.0379) and Flear- cells in monocytes (r=0.4099, p=0.0303). However, a negative correlation was observed between CD3+ cells and hemoglobin (r= -0.4530, p=0.0105). The total CD19+ cells decreased in patients, and CD19+ cells were negatively correlated with LDH (r= -0.5640, p=0.0077) and Flear- cells in monocytes (r= -0.4432, p=0.0341). Patients showed an increased proportion of total dendritic cells (DCs), with a higher proportion of myeloid DCs (mDCs) within the DC population. Moreover, the proportion of mDC/DC was positively correlated with CD59- cells (II + III types) in red cells (r=0.7941, p=0.0004), Flear- cells in granulocytes (r=0.5357, p=0.0396), and monocytes (r=0.6445, p=0.0095).

CONCLUSION

Our results demonstrated that immune abnormalities are associated with PNH development.

Generation of glycosylphosphatidylinositol linked chicken IL-17 to generate specific monoclonal antibodies applicable for intracellular cytokine staining

Interleukin 17 (IL-17) cytokines play a crucial role in host defense and inflammatory diseases. Of the six mammalian IL-17 members five are described in the chicken (gg) genome. A novel method that attached cytokines to the surface of cells via a GPI linker was established to generate two chicken IL-17A and one chicken IL-17F specific mab. Recombinant gg IL-17A and gg IL-17F that showed dimerization in Western blot were used to verify the antibodies specificity. The mab could detect gg IL-17 by intracellular cytokine staining as demonstrated on cells expressing recombinant IL-17. Furthermore IL-17A and lower amounts of IL-17F were detectable in CD4 positive T cells of stimulated splenocytes. In conclusion, we have generated novel tools to analyze chicken IL-17 in more detail and demonstrated that the surface expression of cytokines is a reliable method to generate specific mab applicable for intracellular cytokine staining.

Parasite Carbohydrate Vaccines

Vaccination is an efficient means of combating infectious disease burden globally. However, routine vaccines for the world's major human parasitic diseases do not yet exist. Vaccines based on carbohydrate antigens are a viable option for parasite vaccine development, given the proven success of carbohydrate vaccines to combat bacterial infections. We will review the key components of carbohydrate vaccines that have remained largely consistent since their inception, and the success of bacterial carbohydrate vaccines. We will then explore the latest developments for both traditional and non-traditional carbohydrate vaccine approaches for three of the world's major protozoan parasitic diseases-malaria, toxoplasmosis, and leishmaniasis. The traditional prophylactic carbohydrate vaccine strategy is being explored for malaria. However, given that parasite disease biology is complex and often arises from host immune responses to parasite antigens, carbohydrate vaccines against deleterious immune responses in host-parasite interactions are also being explored. In particular, the highly abundant glycosylphosphatidylinositol molecules specific for Plasmodium, Toxoplasma, and Leishmania spp. are considered exploitable antigens for this non-traditional vaccine approach. Discussion will revolve around the application of these protozoan carbohydrate antigens for vaccines currently in preclinical development.

Interaction between Plasmodium Glycosylphosphatidylinositol and the Host Protein Moesin Has No Implication in Malaria Pathology

Glycosylphosphatidylinositol (GPI) anchor of Plasmodium falciparum origin is considered an important toxin leading to severe malaria pathology through stimulation of pro-inflammatory responses from innate immune cells. Even though the GPI-induced immune response is widely described to be mediated by pattern recognition receptors such as TLR2 and TLR4, previous studies have revealed that these two receptors are dispensable for the development of severe malaria pathology. Therefore, this study aimed at the identification of potential alternative Plasmodium GPI receptors. Herein, we have identified the host protein moesin as an interaction partner of Plasmodium GPI in vitro. Given previous reports indicating the relevance of moesin especially in the LPS-mediated induction of pro-inflammatory responses, we have conducted a series of in vitro and in vivo experiments to address the physiological relevance of the moesin-Plasmodium GPI interaction in the context of malaria pathology. We report here that although moesin and Plasmodium GPI interact in vitro, moesin is not critically involved in processes leading to Plasmodium-induced pro-inflammatory immune responses or malaria-associated cerebral pathology.

Down-regulation of Immune-related Genes by PSCA in Gallbladder Cancer Cells Implanted into Mice

BACKGROUND/AIM

In previous work, we found that prostate stem cell antigen (PSCA) gene, encoding a glycosylphosphatidylinositol-anchored protein, is a presumable tumor suppressor in gastric cancer and gallbladder cancer (GBC). The introduction of PSCA cDNA into GBC cell lines significantly suppressed tumorigenecity of cells in mice. The PSCA protein is thought to be involved in some form of intracellular signaling that remains to be elucidated.

MATERIALS AND METHODS

Using microarrays, we conducted gene-expression profiling on tumors generated by a GBC cell line TGBC-1TKB, with and without expression of PSCA, which was implanted into mice. Genes whose expression was down-regulated by PSCA were selected, and their down-regulation was confirmed by real-time PCR.

RESULTS

We identified several immune-related genes down-regulated by PSCA, including interleukin 8 (IL8), IL1 receptor antagonist (IL1RN) and S100 calcium-binding proteins A8 (S100A8) and A9 (S100A9).

CONCLUSION

PSCA signaling may suppress tumor growth in vivo by modulating immunological characteristics of GBC cells.

Leishmania mexicana infection induces IgG to parasite surface glycoinositol phospholipids that can induce IL-10 in mice and humans

Infection with the intracellular protozoan parasite Leishmania mexicana causes chronic disease in C57BL/6 mice, in which cutaneous lesions persist for many months with high parasite burdens (10(7)-10(8) parasites). This chronic disease process requires host IL-10 and FcγRIII. When Leishmania amastigotes are released from cells, surface-bound IgG can induce IL-10 and suppress IL-12 production from macrophages. These changes decrease IFN-γ from T cells and nitric oxide production in infected cells, which are both required for Leishmania control. However, antibodies targets and the kinetics of antibody production are unknown. Several groups have been unsuccessful in identifying amastigote surface proteins that bind IgG. We now show that glycoinositol phospholipids (GIPLs) of L. mexicana are recognized by mouse IgG1 by 6 weeks of infection, with a rapid increase between 12 and 16 weeks, consistent with the timing of chronic disease in C57BL/6 mice vs. healing in FcγRIII-deficient mice. A single prominent spot on TLC is recognized by IgG, and the glycolipid is a glycosyl phosphatidylinositol containing a branched mannose structure. We show that the lipid structure of the GIPL (the sn-2 fatty acid) is required for antibody recognition. This GIPL is abundant in L. mexicana amastigotes, rare in stationary-phase promastigotes, and absent in L. major, consistent with a role for antibodies to GIPLs in chronic disease. A mouse monoclonal anti-GIPL IgG recognizes GIPLs on the parasite surface, and induces IL-10 from macrophages. The current work also extends this mouse analysis to humans, finding that L. mexicana-infected humans with localized and diffuse cutaneous leishmaniasis have antibodies that recognize GIPLs, can bind to the surface of amastigotes, and can induce IL-10 from human monocytes. Further characterization of the target glycolipids will have important implications for drug and vaccine development and will elucidate the poorly understood role of glycolipids in the immunology of infections.

Functional and immunological analysis of the human sperm proteome

This is a review of ten previously published studies of the human sperm proteome. Proteins expressed on the sperm cell surface were identified and characterized by a combination of vectorial labelling with radioiodine and biotin, PI-PLC treatment, two-dimensional gel electrophoresis, immuno and lectin blotting procedures, affinity overlay assays with radioactive nucleotide triphosphates and 45Ca, and mass spectrometry analysis. Examination of capacitation-induced modifications of the human sperm proteome led to the cloning and characterisation of two new phospho-regulated cancer-testis antigens, which we named Fibrous Sheath Protein 95 (FSP95) and CABYR (calcium-binding tyrosine phosphorylation regulated). A protein kinase A RII binding domain is present between amino acids 124 and 141 identifying FSP95 (now commonly known as AKAP3) as a member of the A kinase anchoring protein-family which provides spatial and temporal specificity to the cAMP-PKA pathway. In addition to scaffolding PKA, PDE and protein phosphatases, AKAPs also bind to a group of four proteins that share homology to the RII dimerization/docking (R2D2) domain of PKA' regulatory subunit. CABYR, which is one of these four proteins, also interacts with a diverse array of signal tranducers via its SH3-, R2D2-, and proline-rich extension-like domains. AKAP3 and CABYR appear to associate in high molecular weight multi-protein complexes, which regulate the flagella' energy supply and movements. Diagonal gel electrophoresis experiments suggest that the high molecular weight signal-integrating scaffold partly is established by homo- and hetero-oligomerization of lower molecular weight splice variants of CABYR. The putative role of CABYR in lung cancer cells is finally discussed.

Complement receptor Mac-1 is an adaptor for NB1 (CD177)-mediated PR3-ANCA neutrophil activation

The glycosylphosphatidylinositol (GPI)-anchored neutrophil-specific receptor NB1 (CD177) presents the autoantigen proteinase 3 (PR3) on the membrane of a neutrophil subset. PR3-ANCA-activated neutrophils participate in small-vessel vasculitis. Since NB1 lacks an intracellular domain, we characterized components of the NB1 signaling complex that are pivotal for neutrophil activation. PR3-ANCA resulted in degranulation and superoxide production in the mNB1(pos)/PR3(high) neutrophils, but not in the mNB1(neg)/PR3(low) subset, whereas MPO-ANCA and fMLP caused similar responses. The NB1 signaling complex that was precipitated from plasma membranes contained the transmembrane receptor Mac-1 (CD11b/CD18) as shown by MS/MS analysis and immunoblotting. NB1 co-precipitation was less for CD11a and not detectable for CD11c. NB1 showed direct protein-protein interactions with both CD11b and CD11a by surface plasmon resonance analysis (SPR). However, when these integrins were presented as heterodimeric transmembrane proteins on transfected cells, only CD11b/CD18 (Mac-1)-transfected cells adhered to immobilized NB1 protein. This adhesion was inhibited by mAb against NB1, CD11b, and CD18. NB1, PR3, and Mac-1 were located within lipid rafts. In addition, confocal microscopy showed the strongest NB1 co-localization with CD11b and CD18 on the neutrophil. Stimulation with NB1-activating mAb triggered degranulation and superoxide production in mNB1(pos)/mPR3(high) neutrophils, and this effect was reduced using blocking antibodies to CD11b. CD11b blockade also inhibited PR3-ANCA-induced neutrophil activation, even when β2-integrin ligand-dependent signals were omitted. We establish the pivotal role of the NB1-Mac-1 receptor interaction for PR3-ANCA-mediated neutrophil activation.

CD160: a unique activating NK cell receptor

Here we discuss CD160 an essential NK cell activating receptor that remains poorly understood. CD160 receptor exhibits a number of unique structural and functional characteristics that are not common to other killer immunoglobulin-like receptors that recognize major histocompatibility complex (MHC) class I molecules: (1) In addition to humans and mice, the cd160 gene is conserved in several other mammal species; (2) cd160 is located outside the NK gene complex and the Leukocyte Receptor Complex in humans; (3) CD160 expression is associated to the CD56(dim) CD16+ cytotoxic NK cell phenotype; (4) both human and mouse CD160 recognize MHC class Ia and Ib molecules; (5) unlike the other MHC class I-dependent activating NK receptors, CD160 is a glycosylphosphatidylinositol-anchored molecule with a single immunoglobulin-like domain, and does not bear immunoreceptor tyrosine-based activation motifs. Consequently, CD160 cannot signal by itself, requiring the recruitment of adaptor proteins. CD160 recruits phosphoinositide-3 kinase to trigger cytotoxicity and cytokine secretion; (6) specific engagement of NK CD160 receptor expressed by circulating NK cells produces proinflammatory cytokines IFN-γ, TNF-α, and, most notably, IL-6 and IL-8 as well as MIP1-β chemokine. The level of CD160-mediated IFN-γ production is always higher than the one observed after engagement of the CD16 receptor.

Scrutinizing the mechanisms underlying the induction of anemia of inflammation through GPI-mediated modulation of macrophage activation in a model of African trypanosomiasis

In animal trypanosomiasis the severity of infection is reflected by the degree of anemia which resembles anemia of inflammation, involving a skewed iron homeostasis leading to iron accumulation within the reticuloendothelial system. Myeloid cells (M cells) have been implicated in the induction and maintenance of this type of anemia and modulation of M cells through the main trypanosome-derived glycosylphosphatidylinositol (GPI)-anchor could attenuate both anemia and trypano-susceptibility in Trypanosoma brucei-infected mice. Herein the GPI-based treatment, allowing a straightforward comparison between trypanotolerance and susceptibility in T. brucei-infected C57Bl/6 mice, was further adopted to scrutinize mechanisms/pathways underlying trypanosome-elicited anemia. Hereby, the following interlinkable observations were made in GPI-based treated (GBT) T. brucei-infected mice: (i) a reduced inflammatory cytokine production and increased IL-10 production associated with alleviation of anemia and restoration of serum iron levels, (ii) a shift in increased liver expression of iron storage towards iron export genes, (iii) increased erythropoiesis in the bone marrow and extramedullar sites (spleen) probably reflecting a normalized iron homeostasis and availability. Collectively, our results demonstrate that reprogramming macrophages towards an anti-inflammatory state alleviates anemia of inflammation by normalizing iron homeostasis and restoring erythropoiesis.

The immunogenic properties of protozoan glycosylphosphatidylinositols in the mosquito Anopheles gambiae

In contrast to humans, mosquitoes do not have an adaptive immune response to deal with pathogens, and therefore must rely on their innate immune system to deal with invaders. This facilitates the recognition of different microbes on the basis of surface components or antigens. Such antigens have been identified in various types of microbe such as bacteria and fungi, yet none has been identified in the genus protozoa, which includes pathogens such as the malaria parasite, Plasmodium falciparum and Toxoplasma gondii. This study allowed us to test the antigenic properties of protozoan glycosylphosphatidylinositol (GPI) on the mosquito immune system. We found that both P. falciparum GPI and T. gondii GPI induce the strong expression of several antimicrobial peptides following ingestion, and that as a result of the immune response against the GPIs, the number of eggs produced by the mosquito is reduced dramatically. Such effects have been associated with malaria infected mosquitoes, but never associated with a Plasmodium specific antigen. This study demonstrates that protozoan GPIs can be considered as protozoan specific immune elicitors in mosquitoes, and that P. falciparum GPI plays a critical role in the malaria parasite manipulation of the mosquito vector to facilitate its transmission.

Activation of TLR2 and TLR4 by glycosylphosphatidylinositols derived from Toxoplasma gondii

GPIs isolated from Toxoplasma gondii, as well as a chemically synthesized GPI lacking the lipid moiety, activated a reporter gene in Chinese hamster ovary cells expressing TLR4, while the core glycan and lipid moieties cleaved from the GPIs activated both TLR4- and TLR2-expressing cells. MyD88, but not TLR2, TLR4, or CD14, is absolutely needed to trigger TNF-alpha production by macrophages exposed to T. gondii GPIs. Importantly, TNF-alpha response to GPIs was completely abrogated in macrophages from TLR2/4-double-deficient mice. MyD88(-/-) mice were more susceptible to death than wild-type (WT), TLR2(-/-), TLR4(-/-), TLR2/4(-/-), and CD14(-/-) mice infected with the ME-49 strain of T. gondii. The cyst number was higher in the brain of TLR2/4(-/-), but not TLR2(-/-), TLR4(-/-), and CD14(-/-), mice, as compared with WT mice. Upon infection with the ME-49 strain of T. gondii, we observed no decrease of IL-12 and IFN-gamma production in TLR2-, TLR4-, or CD14-deficient mice. Indeed, splenocytes from T. gondii-infected TLR2(-/-) and TLR2/4(-/-) mice produced more IFN-gamma than cells from WT mice in response to in vitro stimulation with parasite extracts enriched in GPI-linked surface proteins. Together, our results suggest that both TLR2 and TLR4 receptors may participate in the host defense against T. gondii infection through their activation by the GPIs and could work together with other MyD88-dependent receptors, like other TLRs or even IL-18R or IL-1R, to obtain an effective host response against T. gondii infection.

Assessment of a DNA vaccine encoding an anchored-glycosylphosphatidylinositol tegumental antigen complexed to protamine sulphate on immunoprotection against murine schistosomiasis

Protamine sulphate/DNA complexes have been shown to protect DNA from DNase digestion in a lipid system for gene transfer. A DNA-based vaccine complexed to protamine sulphate was used to induce an immune response against Schistosoma mansoni anchored-glycosylphosphatidylinositol tegumental antigen in BALB/c mice. The protection elicited ranged from 33 to 44%. The spectrum of the elicited immune response induced by the vaccine formulation without protamine was characterized by a high level of IgG (IgG1> IgG2a). Protamine sulphate added to the DNA vaccine formulation retained the green fluorescent protein encoding-plasmid longer in muscle and spleen. The experiments in vivo showed that under protamine sulphate effect, the scope of protection remained unchanged, but a modulation in antibody production (IgG1= IgG2a) was observed.

The GPI-anchored Gas and Crh families are fungal antigens

The cell wall is the first interface between a fungus and its extracellular environment. Glycosyltransferases involved in the formation and dynamic remodelling of the polysaccharide network of the cell wall have recently been identified. The best characterized ones belong to the Gas family, which elongates beta(1,3)-glucans, and to the Crh family, which are involved in the cross-linking of chitin to beta(1,6)-glucan. All these proteins carry a glycosylphosphatidylinositol (GPI) anchor. In this work, we show that recombinant soluble forms of Gas1-5 and Crh1p from Saccharomyces cerevisiae and their orthologous proteins Gel1-Gel2 and Crf1 from Aspergillus fumigatus are specifically recognized by antibodies present in the sera of patients with Aspergillus or Candida infections. Quantification of the antibody titres against recombinant Gas/Gel and Crh/Crf proteins separated aspergilloma and candidiasis patients from non-infected individuals. Cross-reactivity was seen between the antibody response of patients with aspergillosis and candidiasis towards the Gas/Gel and Crh/Crf proteins. These results suggest that GPI-anchored cross-linking enzymes are relevant immunologically reactive constituents of the cell wall that may play a role during human fungal infections.

Disruption of CD36 impairs cytokine response to Plasmodium falciparum glycosylphosphatidylinositol and confers susceptibility to severe and fatal malaria in vivo

CD36 is a scavenger receptor that has been implicated in malaria pathogenesis as well as innate defense against blood-stage infection. Inflammatory responses to Plasmodium falciparum GPI (pfGPI) anchors are believed to play an important role in innate immune response to malaria. We investigated the role of CD36 in pfGPI-induced MAPK activation and proinflammatory cytokine secretion. Furthermore, we explored the role of this receptor in an experimental model of acute malaria in vivo. We demonstrate that ERK1/2, JNK, p38, and c-Jun became phosphorylated in pfGPI-stimulated macrophages. In contrast, pfGPI-induced phosphorylation of JNK, ERK1/2, and c-Jun was reduced in Cd36(-/-) macrophages and Cd36(-/-) macrophages secreted significantly less TNF-alpha in response to pfGPI than their wild-type counterparts. In addition, we demonstrate a role for CD36 in innate immune response to malaria in vivo. Compared with wild-type mice, Cd36(-/-) mice experienced more severe and fatal malaria when challenged with Plasmodium chabaudi chabaudi AS. Cd36(-/-) mice displayed a combined defect in cytokine induction and parasite clearance with a dysregulated cytokine response to infection, earlier peak parasitemias, higher parasite densities, and higher mortality rates than wild-type mice. These results provide direct evidence that pfGPI induces TNF-alpha secretion in a CD36-dependent manner and support a role for CD36 in modulating host cytokine response and innate control of acute blood-stage malaria infection in vivo.

Rational approaches to developing an anti-disease vaccine against malaria

Vaccination against pathogen toxins provides a rational approach to prevent morbidity and mortality, and is widely validated in the context of bacterial infections. A saccharide-conjugate vaccine targeting the malaria glycosylphosphatidylinositol toxin glycan could therefore prevent severe disease. This strategy could also reduce the risk posed by 'rebound' infections or immunopathology associated with other interventions.

Glycosyl-phosphatidyl-inositol-defective granulocytes from paroxysmal nocturnal haemoglobinuria patients show increased bacterial ingestion but reduced respiratory burst induction

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by the emergence of a GPI-defective clonal hematopoiesis. Its clinical features are hemolytic anemia, cytopenia, and thrombosis. Circulating monocytes and granulocytes are largely GPI-defective in PNH patients. This study aims to investigate the granulocyte functional properties in PNH. We analyzed bacterial-dependent intracellular ingestion and the consequent activation of oxidative burst in GPI-defective granulocytes from four neutropenic PNH patients. Our data show a significant increase in the ability of GPI-defective granulocytes to ingest opsonized bacteria. In addition, an impaired respiratory burst effectiveness in response to two independent bacterial stimuli, the N-formyl-MetLeuPhe (fMLP) synthetic bacterial peptide and E. coli, was revealed. The occurrence of neutropenia and the severe impairment of oxidative burst, occurring in chronic granulomatosis disease, were unable to significantly affect phagocytosis. Thus, additional mechanisms, able to differentially affect ingestion ability and respiratory burst effectiveness, have to be hypothesized. The reduced burst effectiveness of GPI-defective granulocytes was maintained after treatment with phorbol 12-myristate 13-acetate, a pharmacological stimulus able to extensively recruit and to trigger intracellular protein kinase C (PKC). Moreover, blocking of PKC has been observed to severely affect granulocyte respiratory burst with a mild effect on the phagocytosis. These data suggest a role for a modulation of intracellular PKC in the pathogenesis of the impaired granulocyte oxidative burst.

Disruption of JNK2 decreases the cytokine response to Plasmodium falciparum glycosylphosphatidylinositol in vitro and confers protection in a cerebral malaria model

Host inflammatory responses to Plasmodium falciparum GPI (pfGPI) anchors are believed to play an important role in the pathophysiology of severe malaria. However, relatively little is known about the signal transduction pathways involved in pfGPI-stimulated inflammatory response and its potential contribution to severe malaria syndromes. In this study, we investigated the role of MAPK activation in pfGPI-induced cytokine secretion and examined the role of selected MAPKs in a model of cerebral malaria in vivo. We demonstrate that ERK1/2, JNK, p38, c-Jun, and activating transcription factor-2 became phosphorylated in pfGPI-stimulated macrophages. A JNK inhibitor (1,9-pyrazoloanthrone) inhibited pfGPI-induced phosphorylation of JNK, c-Jun, and activating transcription factor-2 and significantly decreased pfGPI-induced TNF-alpha secretion. pfGPI-stimulated JNK and c-Jun phosphorylation was absent in Jnk2(-/-) macrophages but unchanged in Jnk1(-/-) and Jnk3(-/-) macrophages compared with wild-type macrophages. Jnk2(-/-) macrophages secreted significantly less TNF-alpha in response to pfGPI than macrophages from Jnk1(-/-), Jnk3(-/-), and wild-type counterparts. Furthermore, we demonstrate a role for JNK2 in mediating inflammatory responses and severe malaria in vivo. In contrast to wild-type or Jnk1(-/-) mice, Jnk2(-/-) mice had lower levels of TNF-alpha in vivo and exhibited significantly higher survival rates when challenged with Plasmodium berghei ANKA. These results provide direct evidence that pfGPI induces TNF-alpha secretion through activation of MAPK pathways, including JNK2. These results suggest that JNK2 is a potential target for therapeutic interventions in severe malaria.

Incorporation of glycosylphosphatidylinositol-anchored granulocyte- macrophage colony-stimulating factor or CD40 ligand enhances immunogenicity of chimeric simian immunodeficiency virus-like particles

The rapid worldwide spread of human immunodeficiency virus (HIV) mandates the development of successful vaccination strategies. Since live attenuated HIV is not accepted as a vaccine due to safety concerns, virus-like particles (VLPs) offer an attractive safe alternative because they lack the viral genome yet they are perceived by the immune system as a virus particle. We hypothesized that adding immunostimulatory signals to VLPs would enhance their efficacy. To accomplish this we generated chimeric simian immunodeficiency virus (SIV) VLPs containing either glycosylphosphatidylinositol (GPI)-anchored granulocyte-macrophage colony-stimulating factor (GM-CSF) or CD40 ligand (CD40L) and investigated their biological activity and ability to enhance immune responses in vivo. Immunization of mice with chimeric SIV VLPs containing GM-CSF induced SIV Env-specific antibodies as well as neutralizing activity at significantly higher levels than those induced by standard SIV VLPs, SIV VLPs containing CD40L, or standard VLPs mixed with soluble GM-CSF. In addition, mice immunized with chimeric SIV VLPs containing either GM-CSF or CD40L showed significantly increased CD4(+)- and CD8(+)-T-cell responses to SIV Env, compared to standard SIV VLPs. Taken together, these results demonstrate that the incorporation of immunostimulatory molecules enhances humoral and cellular immune responses. We propose that anchoring immunostimulatory molecules into SIV VLPs can be a promising approach to augmenting the efficacy of VLP antigens.

Expression and immunogenicity of the Plasmodium falciparum circumsporozoite protein: the role of GPI signal sequence

Previous studies have shown that the immunogenicity of rodent malaria parasite-derived circumsporozoite protein (CS) can be improved by deleting the glycosyl-phosphatidyl-inositol (GPI) signal sequence. To study whether GPI signal sequence deletion would also improve immunogenicity of CS derived from the major plasmodium species causing mortality in humans (P. falciparum), we tested different variants of the P. falciparum CS protein in the context of a live vector-based vaccine carrier (rAd35). We demonstrate that deletion of the GPI signal sequence from CS did not result in altered expression or secretion. In contrast, cellular localization was clearly altered, which perhaps helps to explain the significant improvement of anti-CS antibody and T-cell responses observed in mice using deletion variants in the context of the rAd35 carrier. Our results show that rational design of antigens is warranted for further development of malaria vaccines.

Characterization of Leishmania (Viannia) braziliensis membrane microdomains, and their role in macrophage infectivity

Detergent-resistant membranes (DRMs) from Leishmania (Viannia) braziliensis promastigotes, insoluble in 1% Triton X-100 at 4 degrees C, were fractionated by sucrose density gradient ultracentrifugation. They were composed of glycoinositolphospholipids (GIPLs), inositol phosphorylceramide (IPC), phosphatidylinositol (PI), phosphatidylethanolamine (PE), and sterols. In contrast, 1% Triton X-100-soluble fraction was composed of PE, phosphatidylcholine, phosphatidylserine, PI, IPC, sterol, and lyso-PI. High-performance thin-layer chromatography (HPTLC) immunostaining using monoclonal antibody SST-1 showed that 85% of GIPLs are present in DRMs, and immunoelectron microscopic analysis showed that SST-1-reactive components are located in patches along the parasite surface. No difference in GIPL pattern was observed by HPTLC between Triton X-100-soluble versus -insoluble fractions at 4 degrees C. Analysis of fatty acid composition in DRMs by GC-MS showed the presence of GIPLs containing an alkylacylglycerol, presenting mainly saturated acyl and alkyl chains. DRMs also contained sterol, IPC with saturated fatty acids, PI with at least one saturated acyl chain, and PE with predominantly oleic acid. Promastigotes treated with methyl-beta-cyclodextrin to disrupt lipid microdomains showed significantly lower macrophage infectivity, suggesting a relationship between lipid microdomains and the infectivity of these parasites.

Immune Pathogenesis of Paroxysmal Nocturnal Hemoglobinuria

Somatic mutation in the PIG-A gene is the initial event in the pathogenesis of paroxysmal nocturnal hemoglobinuria (PNH), but the pathophysiologic mechanisms leading to clonal expansion remain unclear. The intricate association of PNH with immune-mediated bone marrow failure syndromes, including aplastic anemia (AA), suggests an immunologic selection process for the glycosylphosphatidyl-inositol (GPI)-deficient hematopoietic clone. The mechanism for the growth advantage of PNH cells may be related to the nature of the antigens targeted by the immune response or to the function of immunomodulatory GPI-anchored proteins on the surface of the hematopoietic target cells. Alternative theories of PNH evolution may include intrinsic properties of the mutated cells, but the experimental evidence is largely lacking. Elucidation of the pathogenesis of PNH may provide key information about the causes of idiopathic AA and help understand the regulation of the hematopoietic stem cell compartment.

Serum antibody levels to glycosylphosphatidylinositols in specimens derived from matched Malian children with severe or uncomplicated Plasmodium falciparum malaria and healthy controls

Neutralizing antibodies to glycosylphosphatidylinositols (GPIs), which are Plasmodium falciparum surface protein anchor molecules implicated in malaria pathogenesis, are thought to protect against symptomatic malaria. Index cases of severe malaria in Malian children 3 months to 14 years of age were matched by age and residence to uncomplicated malaria and healthy controls. Serum antibodies to GPI (IgM and IgG) were measured at the time of severe malaria and after the malaria transmission season. The mean optical density values for IgM and IgG antibodies were higher in children with severe or uncomplicated malaria compared with healthy controls. Similarly, higher percentages of children with IgM and IgG antibodies to GPI were observed in the severe malaria group compared with matched healthy controls. IgG antibody levels to GPI were highest among children with cerebral malaria and children who died. The IgG antibody levels to GPI peaked during periods of malaria transmission and decreased after malaria transmission ended. A direct correlation between age and parasitemia and IgG antibodies to GPI was observed. In summary, higher levels of IgM and IgG antibodies to GPI in young children were associated with disease severity and were short-lived.

Genetic basis for GPI-anchor merozoite surface antigen polymorphism of Babesia and resulting antigenic diversity

Glycosyl-phosphatidylinositol anchor merozoite surface antigens (GPI-anchor MSA) are proposed to act in the invasion process of infective merozoites of Babesia into host erythrocytes. Because of their essential function in the survival of Babesia parasites, they constitute good candidates for the development of vaccines against babesiosis and they have been extensively analyzed. These include Babesia bovis variable MSA (VMSA) and Babesia bigemina gp45/gp55 proteins of the agents of bovine babesiosis from tropical and subtropical countries, and the Babesia divergens Bd37 and Babesia canis Bc28 proteins of the main agents of bovine and canine babesiosis in Europe, respectively. However, these are very polymorphic antigens and Babesia parasites have evolved molecular mechanisms that enable these antigens to evade the host immune system as a survival strategy. This review focuses on the genetic basis of GPI-anchor MSA polymorphism and the antigenic diversity of B-cell epitopes that might be generated in each of these Babesia species. The picture is incomplete and no Babesia genome sequence is yet available. However, the available sequences suggest that two distinct, non cross-reactive GPI-anchor MSA (i.e., with unique B-cell epitopes) may be required by all Babesia species for invasion, and that these two distinct GPI-anchor MSA would be encoded by a multigene family. Furthermore, the data are consistent with the ability of biological clones from Babesia to use these multigene families for the expression of GPI-anchor MSA, either conserved (B. canis and B. bovis) or polymorphic (B. divergens and B. bigemina) in their amino acid sequence. Moreover, as a consequence for successful parasitism, the data suggest that both conserved and polymorphic GPI-anchor MSA would present unique B-cell epitopes.

Naturally elicited antibodies to glycosylphosphatidylinositols (GPIs) of Plasmodium falciparum require intact GPI structures for binding and are directed primarily against the conserved glycan moiety

Immunization with a synthetic glycan corresponding to Plasmodium falciparum glycosylphosphatidylinositols (GPIs) has been proposed as a vaccination strategy against malaria. We investigated the structural requirements for binding of naturally elicited anti-GPI antibodies to parasite GPIs. The data show that anti-GPI antibody binding requires intact GPI structures and that the antibodies are directed predominantly against GPIs with a conserved glycan structure with three mannoses and marginally against the terminal fourth mannose. The results provide valuable insight for exploiting GPIs for the development of malaria vaccines.

Immunoselection by natural killer cells of PIGA mutant cells missing stress-inducible ULBP

The mechanism by which paroxysmal nocturnal hemoglobinuria (PNH) clones expand is unknown. PNH clones harbor PIGA mutations and do not synthesize glycosylphosphatidylinositol (GPI), resulting in deficiency of GPI-linked membrane proteins. GPI-deficient blood cells often expand in patients with aplastic anemia who sustain immune-mediated marrow injury putatively induced by cytotoxic cells, hence suggesting that the injury allows PNH clones to expand selectively. We previously reported that leukemic K562 cells preferentially survived natural killer (NK) cell-mediated cytotoxicity in vitro when they acquired PIGA mutations. We herein show that the survival is ascribable to the deficiency of stress-inducible GPI-linked membrane proteins ULBP1 and ULBP2, which activate NK and T cells. The ULBPs were detected on GPI-expressing but not on GPI-deficient K562 cells. In the presence of antibodies to either the ULBPs or their receptor NKG2D on NK cells, GPI-expressing cells were as less NK sensitive as GPI-deficient cells. NK cells therefore spared ULBP-deficient cells in vitro. The ULBPs were identified only on GPI-expressing blood cells of a proportion of patients with PNH but none of healthy individuals. Granulocytes of the patients partly underwent killing by autologous cytotoxic cells, implying ULBP-associated blood cell injury. In this setting, the lack of ULBPs may allow immunoselection of PNH clones.

GPI-linked endothelial CD14 contributes to the detection of LPS

The inflammatory endothelial response to LPS is critical to the host's surviving a gram-negative bacterial infection. In this study we investigated whether human endothelial cells express the functional coreceptor for LPS, CD14, and most importantly whether it is glycosylphosphatidylinositol (GPI) linked. We also examined whether plasma proteins could reconstitute an LPS response in CD14-inhibited endothelium. RT-PCR- and CD14-specific MAbs demonstrated CD14 expression on primary human umbilical vein endothelial cells (HUVEC) but not passaged HUVEC. The amino acid sequence of endothelial CD14 was 99% homologous to CD14 on monocytes. Endothelium responded to relatively low levels of LPS in the absence of plasma, and this was entirely dependent on CD14. Removal of GPI-linked proteins with phosphatidylinositol-phospholipase C prevented LPS detection and subsequent protein synthesis (E-selectin expression). Endothelial CD14 was sufficient to initiate functional leukocyte recruitment, an event inhibited by blocking its LPS binding epitope and also by removing CD14 from the endothelial surface. Plasma proteins restored only approximately 30% of the LPS response in CD14-inhibited endothelium. In conclusion, our results strongly support an important role for endothelial membrane CD14 in the activation of endothelium for leukocyte recruitment.

Toxoplasma gondii grown in human cells uses GalNAc-containing glycosylphosphatidylinositol precursors to anchor surface antigens while the immunogenic Glc–GalNAc-containing precursors remain free at the parasite cell surface

Toxoplasma gondii is a ubiquitous parasite that infects nearly all warm-blooded animals. Developmental switching in T. gondii, from the virulent tachyzoite to the relatively quiescent bradyzoite stage, is responsible for the disease propagation after alteration of the immune status of the carrier. The redifferentiation event is characterized by an over expression of a tachyzoite specific set of glycosylphosphatidylinositol anchored surface antigens and free GPIs. T. gondii grown in animal cells uses two glycosylphosphatidylinositol precursors to anchor the parasite surface proteins. The first form has an N-acetylgalactosamine residue bound to a conserved three-mannosyl core glycan, while the second structure contains an additional terminal glucose linked to the N-acetylgalactosamine side branch. Sera from persons infected with T. gondii reacted only with the glucose-N-acetylgalactosamine-containing structure. Here we report that T. gondii cultured in human cells uses predominantly the N-acetylgalactosamine-containing structure to anchor the parasite surface antigens. On the other hand, glycosylphosphatidylinositol structures having an additional terminal glucose are found exclusively on the parasite cell surface as free glycolipids participating in the production of cytokines that are implicated in the pathogenesis of T. gondii. We also provide evidence that such free glycosylphosphatidylinositols are restricted mainly to the lipid microdomains in the parasite cell surface membrane and mostly associated with proteins involved in the parasite motility as well as invasion of the host cell.

Regulating immunity to malaria

The optimal outcome of a malaria infection is that parasitized cells are killed and degraded without inducing significant pathology. Since much of the pathology of malaria infection can be immune-mediated, this implies that immune responses have to be carefully regulated. The mechanisms by which anti-malarial immune responses are believed to be regulated were discussed at the recent Malaria Immunology Workshop (Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA; February 2005). Potential regulatory mechanisms include regulatory T cells, which have been shown to significantly modify cellular immune responses to various protozoan infections, including leishmania and malaria; neutralising antibodies to pro-inflammatory malarial toxins such as glycosylphosphatidylinositol and haemozoin; and self-regulating networks of effector molecules. Innate and adaptive immune responses are further moderated by the broader immunological environment, which is influenced by both the genetic background of the host and by co-infection with other pathogens. A detailed understanding of the interplay between these different immunoregulatory processes may facilitate the rationale design of vaccines and novel therapeutics.

Where Do T Cells Stand in Rheumatoid Arthritis?

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by destruction of cartilage and bone. The destructive lesions result from both immune responses and non-antigen-specific inflammatory processes. Little is known about the primary cause of RA. Although the primacy of T-cell-related events early in the disease remains debated, strong evidence indicates that autoantigen recognition by specific T cells is crucial to the pathophysiology of rheumatoid synovitis. We will discuss evolving concepts about T-cell involvement in RA and the roles for various T cell subsets in the development of joint abnormalities. The hypothesis that RA is a T-cell driven disease was put forward when studies of RA synovium showed numerous T cells carrying activation markers. These T cells were found to participate in the complex network of cell- and mediator-driven events leading to joint destruction. Conceivably, these T cells may be stimulated by an autoantigen (whether specific to the joints or ubiquitous), a highly conserved foreign protein cross-reacting with its human homolog, or a neo-antigen expressed as a result of posttranslational events. For many years, animal models have provided valuable evidence supporting a role for T cells in RA. We will review three murine models of arthritis caused by different mechanisms. In collagen-induced arthritis, the immune response to a joint antigen is mediated by pathogenic Th1 cells that elicit severe inflammatory synovitis. Spontaneous arthritis in K/BxN T-cell-receptor transgenic mice is related to an adaptive immune response against a ubiquitous protein whose end-stage effector mechanisms are heavily dependent on the innate immune system. In the SKG model of autoimmune inflammatory arthritis, a point mutation in the gene encoding a key signal-transduction molecule in T cells causes defective T cell selection in the thymus, which releases polyclonal autoreactive T cells. Studies in these and other animal models have established that a variety of T-cell subsets whose roles vary with cell location and disease stage can contribute to synovitis. Finally, in addition to direct autoimmune attack by effector T cells, arthritis may result from defective homeostatic control of immunity by regulatory T cells.

Epitope analysis of immunoglobulins against gp20, a GPI-anchored protein of the human sperm surface homologous to leukocyte antigen CD52

Gp20 is a sialylglycoprotein of the human sperm surface related to maturation and capacitation and is homologous to CD52, a glycosyl- phosphatidyl-inositol (GPI)-anchored protein highly expressed in lymphocytes, monocytes, eosinophils, and epididymal cells, described by the monoclonal antibody family CAMPATH. The CAMPATH antigen is characterized by a very short peptide (12 amino acids) and an N-linked oligosaccharide chain bound to the asparagine located in the third position and a GPI anchor bound to the C-terminal serine. The CAMPATH epitope includes three amino acids at the C-terminus and part of the GPI anchor. It has been suggested that anti-gp20 interacts with the same peptide recognized by CAMPATH antibodies but with a different epitope, since it describes the corresponding antigen in a different way. For example, it localizes the corresponding antigen in the equatorial region of the sperm head when sperm are capacitated, whereas CAMPATH antibodies bind all over the sperm surface. Our results indicate that the anti-gp20 epitope does not include the peptide backbone, the GPI anchor, or the N-glycans but consists of O-linked oligosaccharide chains bound to a unique CD52 glycoform present both in sperm and leukocytes. This is suggested by results obtained using many different approaches, such as immunoblot analysis of gp20 after removal of N- and O-glycans and after jacalin (Artocarpus integrifolia agglutinin)-affinity chromatography.

Induction of nitric oxide synthase in Anopheles stephensi by Plasmodium falciparum: mechanism of signaling and the role of parasite glycosylphosphatidylinositols

Malaria parasite (Plasmodium spp.) infection in the mosquito Anopheles stephensi induces significant expression of A. stephensi nitric oxide synthase (AsNOS) in the midgut epithelium as early as 6 h postinfection and intermittently thereafter. This induction results in the synthesis of inflammatory levels of nitric oxide (NO) in the blood-filled midgut that adversely impact parasite development. In mammals, P. falciparum glycosylphosphatidylinositols (PfGPIs) can induce NOS expression in immune and endothelial cells and are sufficient to reproduce the major effects of parasite infection. These effects are mediated in part by mimicry of insulin signaling by PfGPIs. In this study, we demonstrate that PfGPIs can induce AsNOS expression in A. stephensi cells in vitro and in the midgut epithelium in vivo. Signaling by P. falciparum merozoites and PfGPIs is mediated through A. stephensi Akt/protein kinase B and a pathway involving DSOR1, a mitogen-activated protein kinase kinase, and an extracellular signal-regulated kinase. However, despite the involvement of kinases that are also associated with insulin signaling in A. stephensi cells, signaling by P. falciparum and by PfGPIs is distinctively different from signaling by insulin. Therefore, although mimicry of insulin by PfGPIs appears to be restricted to mammalian hosts of P. falciparum, the conservation of PfGPIs as a prominent parasite-derived signal of innate immunity can now be extended to include Anopheles mosquitoes, indicating that parasite signaling of innate immunity is conserved in mosquito and mammalian cells.

Cloning of a glycosylphosphatidylinositol-anchored alpha-2-macroglobulin cDNA from the ascidian, , and its possible role in immunity

Molecular approaches were used to study thiolester-containing genes in the ascidian, Ciona intestinalis. RT-PCR, RACE and genome mining revealed that this animal expresses not only conventional alpha-2-macroglobulin (alpha2m) and two forms of C3 but also a gene encoding a glycosylphosphatidylinositol (GPI)-anchored alpha2m. Previously, GPI-anchored alpha2ms have been reported only for humans and mice. We propose that GPI-anchored alpha2ms constitute a third subgroup of the alpha2m superfamily and may represent an important evolutionary stage in the phylogeny of the thiolester containing proteins. Its occurrence in an ascidian shows its origin pre-dates the evolution of the vertebrates. In C. intestinalis this GPI-anchored alpha2m, designated Ciona alpha2m-GPI, is expressed in the hepatopancreas, circulating coelomic blood cells and the gut of adults. It is also expressed in 3-5 days old larvae. Its tissue distribution coupled with its sequence characteristics and unusual domain structure indicate that the encoded protein probably assists in host defence by entrapping and inhibiting proteases from micro-organisms.

Differential antibody responses to Plasmodium falciparum glycosylphosphatidylinositol anchors in patients with cerebral and mild malaria

Glycosylphosphatidylinositol (GPI) membrane anchors of Plasmodium falciparum surface proteins are thought to be important factors contributing to malaria pathogenesis, and anti-GPI antibodies have been suggested to provide protection by neutralizing the toxic activity of GPIs. In this study, IgG responses against P. falciparum GPIs and a baculovirus recombinant MSP1p19 antigen were evaluated in two distinct groups of 70 patients each, who were hospitalized with malaria. Anti-GPI IgGs were significantly lower in patients hospitalized with confirmed cerebral malaria compared to those with mild malaria (P < 0.01) but did not discriminate for fatal outcome. In contrast, a specific marker of the anti-parasite immunity, as monitored by the anti-MSP1p19 IgG response, was similar in both cerebral and mild malaria individuals, although it was significantly lower in a subgroup with fatal outcomes. These results are consistent with a potential anti-toxin role for anti-GPI antibodies associated with protection against cerebral malaria.

Glycosylphosphatidylinositols in malaria pathogenesis and immunity: potential for therapeutic inhibition and vaccination

Glycosylphosphatidylinositols (GPIs) are found in the outer cell membranes of all eukaryotes. GPIs anchor a diverse range of proteins to the surface of Plasmodium falciparum, but may also exist free of protein attachment. In vitro and in vivo studies have established GPIs as likely candidate toxins in malaria, consistent with the prevailing paradigm that attributes induction of inflammatory cytokines, fever and other pathology to parasite toxins released when schizonts rupture. Although evolutionarily conserved, sufficient structural differences appear to exist that impart upon plasmodial GPIs the ability to activate second messengers in mammalian cells and elicit immune responses. In populations exposed to P. falciparum, the antibody response to purified GPIs is characterised by a predominance of immunoglobulin (Ig)G over IgM and an increase in the prevalence, level and persistence of responses with increasing age. It remains unclear, however, if these antibodies or other cellular responses to GPIs mediate anti-toxic immunity in humans; anti-toxic immunity may comprise either reduction in the severity of disease or maintenance of the malaria-tolerant state (i.e. persistent asymptomatic parasitaemia). P. falciparum GPIs are potentially amenable to specific therapeutic inhibition and vaccination; more needs to be known about their dual roles in malaria pathogenesis and protection for these strategies to succeed.

Lack of an association between antibodies to Plasmodium falciparum glycosylphosphatidylinositols and malaria-associated placental changes in Cameroonian women with preterm and full-term deliveries

Sequestration of Plasmodium falciparum parasites within the placenta often leads to an accumulation of macrophages within the intervillous space and increased production of tumor necrosis factor alpha (TNF-alpha), a cytokine associated with placental pathology and poor pregnancy outcomes. P. falciparum glycosylphosphatidylinositol (GPI) anchors have been shown to be the major parasite component that induces TNF-alpha production by monocytes and macrophages. Antibodies against P. falciparum GPI (anti-PfGPI), however, can inhibit the induction of TNF-alpha and inflammation. Thus, the study was undertaken to determine whether anti-PfGPI antibodies down-regulate inflammatory-type changes in the placentas of women with malaria. Anti-PfGPI immunoglobulin M (IgM) and IgG levels were measured in 380 pregnant women with or without placental malaria, including those who delivered prematurely and at term. Results showed that anti-PfGPI antibody levels increased with gravidity and age and that malaria infection boosted anti-PfGPI antibodies in pregnant women. However, no association was found between anti-PfGPI antibodies and placental TNF-alpha levels or the presence of acute or chronic placental malaria. Furthermore, anti-PfGPI antibody levels were similar in women with preterm and full-term deliveries and were not associated with an increase in infant birth weight. Thus, these results fail to support a strong role for anti-PfGPI antibodies in the prevention of chronic placental malaria infections and malaria-associated poor birth outcomes.

[Preparation of mB7.1-GPI and SEA-TM dual-anchored tumor cell vaccine and its antitumor effect]

OBJECTIVE

To prepare the SEA-TM and mB7.1-GPI dual-anchored EL-4 cell vaccine and to investigate its antitumor effects.

METHODS

mB7.1-GPI-anchored EL-4 cell vaccine, SEA-TM-anchored EL-4 cell vaccine, SEA-TM and mB7.1-GPI dual-anchored EL-4 cell vaccine were prepared. In vitro the biological activities of these vaccines were measured using a lymphocyte proliferation assay and cytokine release assay on splenocytes derived from C57BL/6 mice. The splenocytes were co-cultured with EL-4 or EL-4/mB7.1-GPI or EL-4/SEA-TM or EL-4/SEA-TM + mB7.1-GPI (treated with Mitomycin C). Lymphocyte proliferation was determined with MTT assay, the concentrations of cytokines (IL-2 and IFN-gamma) were measured using a ELISA technique. Forty C57BL/6 mice were inoculated with EL-4 cells, after 3 days the mice were randomly divided into 5 groups with 8 in each and were treated with PBS, EL-4 cell vaccine, EL-4/mB7.1-GPI cell vaccine, EL-4/SEA-TM cell vaccine and EL-4/SEA-TM + mB7.1-GPI cell vaccine respectively, vaccines were injected three time with two-day interval. Animals were observed daily, tumor sizes were measured every third day. Twenty-five days after tumor challenge, 3 mice in each group were sacrificed and splenic lymphocytes were isolated to examine the activity of natural killer cells (NK) and cytolytic T lymphocytes (CTL). The survival of the remaining 5 mice in each group was observed till the 90th day.

RESULTS

mB7.1-GPI or/and TM-SEA fusion protein was stably anchored onto the surface of EL-4 tumor cells. EL-4/mB7.1-GPI or EL-4/SEA-TM had a stronger ability to stimulate lymphocyte proliferation and IL-2 and IFN-gamma production than EL-4 (P < 0.05); while EL-4/SEA-TM + mB7.1-GPI showed a further increased ability than EL-4/mB7.1-GPI and EL-4/SEA-TM in stimulating lymphocyte proliferation and cytokine production in vitro (P < 0.05). Volume of tumor was smaller and survival time of mice was longer in EL-4/mB7.1-GPI vaccine group, EL-4/SEA-TM vaccine group and EL-4/SEA-TM + mB7.1-GPI vaccine group, comparing with PBS group and EL-4 cell vaccine group (P < 0.05). Tumor volume was much smaller and survival time of mice was much longer in EL-4/mB7.1-GPI + mB7.1-GPI vaccine group, comparing with EL-4/SEA-TM vaccine group and EL-4/mB7.1-GPI vaccine group (P < 0.05). Lymphocytes derived from the mice treated with EL-4/SEA-TM + mB7.1-GPI showed much higher NK activity and CTL activity than those derived from EL-4/mB7.1-GPI vaccine group and EL-4/SEA-TM vaccine group (P < 0.05), meanwhile the NK activity and CTL activity of EL-4/mB7.1-GPI vaccine group and EL-4/SEA-TM vaccine group was higher than EL-4 vaccine group (P < 0.05).

CONCLUSION

mB7.1-GPI or/and SEA-TM fusion protein was stably anchored onto the surface of EL-4 tumor cells. The tumor cell vaccines prepared from these cells exhibited antitumor effect. The mB7.1-GPI and SEA-TM dual-anchored tumor cell vaccine had much stronger antitumor effect than the single-anchored tumor cell vaccine.

Enhanced protective immunity against malaria by vaccination with a recombinant adenovirus encoding the circumsporozoite protein of Plasmodium lacking the GPI-anchoring motif

A major malaria vaccine candidate, the circumsporozoite (CS) protein of Plasmodium, is a pre-erythrocytic stage antigen that is attached to the surface of the sporozoites through a glycosylphosphatidylinositol (GPI) anchor. However, here we show that the motif that signals for glycosylphosphatidylinositol anchor addition interferes with the immunogenicity of this protein and reduces protection in mice upon immunization with a recombinant adenovirus. The presence of the glycosylphosphatidylinositol-anchoring motif sequentially affected total circumsporozoite protein production, cellular distribution, antigen processing and secretion, leading to less effective antigen presentation. Consistently, vaccination with an adenovirus recombinant carrying the anchoring motif-disrupted circumsporozoite gene, resulted in significant increase of the number of interferon-gamma (IFN-gamma) producing T cells and specific IgG2a isotype antibodies, ensuing more effective vaccination. Given that the anchoring motif is highly conserved among different species of Plasmodium, anti-malaria subunit vaccines encoded by recombinant vectors that aim at the induction of strong cellular immunity could maximize immunogenicity by removing anchoring motifs.

Surface sialic acids taken from the host allow trypanosome survival in tsetse fly vectors

The African trypanosome Trypanosoma brucei, which causes sleeping sickness in humans and Nagana disease in livestock, is spread via blood-sucking Tsetse flies. In the fly's intestine, the trypanosomes survive digestive and trypanocidal environments, proliferate, and translocate into the salivary gland, where they become infectious to the next mammalian host. Here, we show that for successful survival in Tsetse flies, the trypanosomes use trans-sialidase to transfer sialic acids that they cannot synthesize from host's glycoconjugates to the glycosylphosphatidylinositols (GPIs), which are abundantly expressed on their surface. Trypanosomes lacking sialic acids due to a defective generation of GPI-anchored trans-sialidase could not survive in the intestine, but regained the ability to survive when sialylated by means of soluble trans-sialidase. Thus, surface sialic acids appear to protect the parasites from the digestive and trypanocidal environments in the midgut of Tsetse flies.

Entamoeba histolytica trophozoites transfer lipophosphopeptidoglycans to enteric cell layers

Transfer of antigens frequently follows adhesion of protozoan parasites to host cells. We were interested in such transfer from the Entamoeba surface to enterocytes following adhesion of trophozoites. Therefore, cocultures of enterocytes in vitro and ex vivo with Entamoeba histolytica (strain HM-1:IMSS) or Entamoeba dispar (strain SAW760) trophozoites were processed for immunocytochemistry. The EH5 monoclonal antibody against amoebic proteophosphoglycans marked a dotted pattern on the apical side of enterocytes in in vitro cocultures with HM-1:IMSS and SAW760 trophozoites. Basolateral staining was present in cocultures following dysfunction of tight junctions, or when trophozoites made direct contact with the basolateral side of enterocytes in in vitro and ex vivo cocultures. Based on the molecular mass in Western blot, the transferred proteophosphoglycan was identified as a lipophosphopeptidoglycan. In conclusion, trophozoites transfer LPPG to the apical side of enterocytes following adhesion and prior to dysfunction of tight junctions.

In vitro and in vivo evidence of PNH cell sensitivity to immune attack after nonmyeloablative allogeneic hematopoietic cell transplantation

It has been proposed that paroxysmal nocturnal hemoglobinuria (PNH) cells may proliferate through their intrinsic resistance to immune attack. To evaluate this hypothesis, we examined the impact of alloimmune pressure on PNH and normal cells in the clinical setting of nonmyeloablative allogeneic hematopoietic cell transplantation (HCT). Five patients with severe PNH underwent HCT from an HLA-matched family donor after conditioning with cyclophosphamide and fludarabine. PNH neutrophils (CD15(+)/CD66b(-)/CD16(-)) were detected in all patients at engraftment, but they subsequently declined to undetectable levels in all cases by 4 months after transplantation. To test for differences in susceptibility to immune pressure, minor histocompatibility antigen (mHa)-specific T-cell lines or clones were targeted against glycosylphosphatidylinositol (GPI)-negative and GPI-positive monocyte and B-cell fractions purified by flow cytometry sorting. Equivalent amounts of interferon-gamma (IFN-gamma) were secreted following coculture with GPI-negative and GPI-positive targets. Furthermore, mHa-specific T-cell lines and CD8(+) T-cell clones showed similar cytotoxicity against both GPI-positive and GPI-negative B cells. Presently, all 5 patients survive without evidence of PNH 5 to 39 months after transplantation. These in vitro and in vivo studies show PNH cells can be immunologically eradicated following nonmyeloablative HCT. Relative to normal cells, no evidence for a decreased sensitivity of PNH cells to T-cell-mediated immunity was observed.

Age-dependent impairment of IgG responses to glycosylphosphatidylinositol with equal exposure to Plasmodium falciparum among Javanese migrants to Papua, Indonesia

Immune responses directed at glycosylphosphatidylinositol (GPI) anchors of Plasmodium falciparum may offer protection against symptomatic malaria. To independently explore the effect of age on generation of the anti-GPI IgG response, we measured serum anti-GPI IgGs in a longitudinal cohort of migrant Javanese children (6-12 years old) and adults (> or = 20 years old) with equivalent numbers of exposures to P. falciparum in Papua, Indonesia. While the peak response in adults was achieved after a single infection, comparable responses in children required > or = 3-4 infections. Significantly fewer children (16%) than adults (41%) showed a high (optical density > 0.44) anti-GPI IgG response (odds ratio [OR] = 3.8, 95% confidence interval [CI] = 2.3-6.3, P < 0.0001), and adults were more likely to show a persistently high response (OR = 5.5, 95% CI = 1.0-56.8, P = 0.03). However, the minority of children showing a strong response were significantly less likely to experience symptoms with subsequent parasitemia compared with those with a weak response (OR = 4.0, 95% CI = 1.1-13.8, P = 0.02). This effect was not seen among high- and low-responding adults (OR = 1.2, 95% CI = 0.5-2.8, P = 0.60). Host age, independent of cumulative exposure, apparently represents a key determinant of the quantitative and qualitative nature of the IgG response to P. falciparum GPI.

Immunoglobulin G (IgG) responses to Plasmodium falciparum glycosylphosphatidylinositols are short-lived and predominantly of the IgG3 subclass

The induction of neutralizing immunity to Plasmodium falciparum toxins by vaccination has been proposed as a preventive strategy to limit the severity of malaria. For this approach to be successful, generation of a sustained immune response would be necessary. This study shows that immunoglobulin G (IgG)-subclass responses elicited by the proposed P. falciparum toxin glycosylphosphatidylinositol (GPI) in Papua New Guinean subjects 5-60 years old predominantly involve IgG(3), with a lesser contribution from IgG(1) and an absence of IgG(2) and IgG(4). IgG(3) levels declined sharply within 6 weeks of pharmacological clearance of parasitemia in all subjects, whereas a significant decrease in IgG(1) levels was seen only in subjects < or =19 years old. Because the natural antibody response to P. falciparum GPIs is skewed toward the short-lived IgG(3) subclass, a vaccination strategy with GPI analogues would likely require augmentation by costimulatory molecules, to induce a more persistent anti-GPI response.

Impaired expression of erythrocyte glycosyl-phosphatidylinositol-anchored membrane CD59 in patients with psoriatic arthritis. Relation to terminal complement pathway activation

OBJECTIVE

Complement-mediated injury is regulated by many factors; among these CD59 has been identified as a widely distributed glycoprotein that inhibits membrane C5b-9 (terminal complement component) formation. The aim of the study was to assess erythrocyte CD59 expression in patients with psoriatic arthritis in order to understand the role of CD59 in the pathogenesis.

METHODS

Washed erythrocytes from 50 patients with psoriatic arthritis, 8 with cutaneous psoriasis and 24 healthy subjects were incubated with monoclonal anti-CD59 antibody followed by a second FITC conjugated antibody and fluorescence intensity analysed by FAC-Scan flow cytometer to assess their CD59 membrane expression. SC5b-9 levels were measured in the plasma by ELISA and results compared with CD59 values. Immune complexes, complement C3 and C4 and rheumatoid factor were also determined.

RESULTS

Impaired expression of erythrocyte membrane-anchored CD59 was found in patients with psoriatic arthritis; the lowest levels were seen in active patients (p < 0.01). Increased SC5b-9 was seen in the plasma of patients with active disease. An inverse correlation was also found between plasma C5b-9 and the CD59 expression levels (r = -0.81, p < 0.001).

CONCLUSION

The low CD59 expression on erythrocytes from patients with psoriatic arthritis may be an index of a low tissue CD59 expression. This impairment could facilitate the activation of complement pathway and increase the risk for arthritis. Membrane attack complex formation in deficient membrane bound CD59 may also exacerbate synovial cell injury and inflammation.

Seeing the good and bad in aplastic anemia: is autoimmunity in AA dysregulated or antineoplastic?

Aplastic anemia (AA) is considered to be an autoimmune disease directed against hematopoietic stem cells (HSC), though knowledge on the inciting autoantigen(s) is scant. According to the traditional concept of autoimmunity the target tissue in autoimmune disease is essentially normal, and misdirected self-attack is caused by disturbed self-recognition. Recently, this theory has been challenged by the hypothesis that autoimmunity against solid tissues is directed against intrinsically abnormal, transforming cells, i.e. autoimmune reactions are essentially antineoplastic, attempting to eliminate cells signalling 'danger'. This theory might apply to AA as well. Observations such as the dysplastic traits typical of non-severe AA, the high prevalence of one or several abnormal hematopoietic clones and their resistance to apoptosis in newly diagnosed AA patients suggest that these cell populations do not develop secondarily, but expand primarily und could be the primary target of AA, normal hematopoietic stem cells being destroyed as innocent bystanders. If bone marrow hypoplasia/aplasia indeed reflects an immune reaction incited by outgrowth of transformed cells, immunosuppressive treatment of AA would have to be reconsidered, since a two-edged sword. As a consequence, AA patients with a hyperreactive immune system may require more intense immunosuppressive therapy (IS), whereas patients with an anergic immune system may fare better with IS of lower intensity than the currently recommended standard.

Pathogenesis of selective expansion of PNH clones

Hemolysis, a characteristic of paroxysmal nocturnal hemoglobinuria (PNH), is caused by the expansion of an affected stem cell with a mutation of the PIG-A gene. Increasing evidence has shown that the presence of the PIG-A mutation alone does not induce the expansion. Two theories have been proposed. One, the growth advantage hypothesis, is supported by current data indicating the presence of several intrinsic alterations that might confer a proliferative advantage to PNH clones over normal cells. Alternatively, the PIG-A mutation might confer a relative survival advantage to PNH clones. This theory is supported by clinical observation indicating that PIG-A mutant cells survive immune-mediated bone marrow injury in patients with aplastic anemia, PNH, and myelodysplastic syndromes. The latter theory is also supported by current experimental data indicating that PIG-A mutant cells are relatively resistant to cytotoxic attack by natural killer cells and cytotoxic T-lymphocytes. The 2 theories appear complementary rather than mutually exclusive. Rapid progress in this field can be expected in the near future.

Inefficient response of T lymphocytes to glycosylphosphatidylinositol anchor-negative cells: implications for paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a hematopoietic stem cell disorder in which clonal cells defective in glycosylphosphatidylinositol (GPI) biosynthesis are expanded, leading to complement-mediated hemolysis. PNH is often associated with bone marrow suppressive conditions, such as aplastic anemia. One hypothetical mechanism for the clonal expansion of GPI(-) cells in PNH is that the mutant cells escape attack by autoreactive cytotoxic cells that are thought to be responsible for aplastic anemia. Here we studied 2 model systems. First, we made pairs of GPI(+) and GPI(-) EL4 cells that expressed major histocompatibility complex (MHC) class II molecules and various types of ovalbumin. When the GPI-anchored form of ovalbumin was expressed on GPI(+) and GPI(-) cells, only the GPI(+) cells presented ovalbumin to ovalbumin-specific CD4(+) T cells, indicating that if a putative autoantigen recognized by cytotoxic cells is a GPI-anchored protein, GPI(-) cells are less sensitive to cytotoxic cells. Second, antigen-specific as well as alloreactive CD4(+) T cells responded less efficiently to GPI(-) than GPI(+) cells in proliferation assays. In vivo, when GPI(-) and GPI(+) fetal liver cells, and CD4(+) T cells alloreactive to them, were cotransplanted into irradiated hosts, the contribution of GPI(-) cells in peripheral blood cells was significantly higher than that of GPI(+) cells. The results obtained with the second model suggest that certain GPI-anchored protein on target cells is important for recognition by T cells. These results provide the first experimental evidence for the hypothesis that GPI(-) cells escape from immunologic attack.

A GPI-linked isoform of the IgD receptor regulates resting B cell activation

The induction of a humoral response depends upon efficient cross-linking by antigen of surface immunoglobulin on primary B lymphocytes. We demonstrate here the presence of a glycosylphosphatidylinositol-linked isoform of membrane IgD (mIgD) receptors on murine resting B cells. This subset was constitutively localized to cell membrane raft microdomains. Its stimulation resulted in the activation of cAMP-dependent signaling pathways, which integrated with signals derived from the transmembrane mIgD receptors. This, in turn, provided a mechanism by which the activation status of the target cells could be variably regulated. Thus, by partitioning receptor activity, preimmune B cells can moderate the extent to which they are activated, depending upon the strength of the antigenic stimulus.

Interactions of integrins with their partner proteins in leukocyte membranes

Integrins participate in many aspects of immunologic and inflammatory responses, especially those involving cell migration, adherence, and activation. Although leukocyte integrins such as complement receptor type 3 (CR3) are known to carry out certain functions without the intervention of other plasma membrane receptors, many plasma membrane proteins are now known to physically interact and functionally cooperate with integrins. Several of these interactions are highly dynamic within cell membranes; thus integrin-partner protein interactions change during certain physiological processes. This allows an extraordinary adaptability of the system to prime and promote proinflammatory signaling. Since our discovery of the CR3-FcgammaRIIIB interaction, the plasma membrane protein repertoire of beta1, beta2, and beta3 integrins has grown to include: FcgammaRIIA (CD32), uPAR (urokinase-type plasminogen activator receptor; CD87), CD14, voltage-gated K+channels (Kv1.3), integrin-associated protein (IAP), CD98, tetraspans (TM4SF), insulin receptors, and PDGFbeta receptors. In this article we will highlight certain features of this growing field of research, especially with regard to their relevance in immunology and inflammation.