Neutrophil alterations in pregnancy-associated malaria and induction of neutrophil chemotaxis by Plasmodium falciparum.

Pregnancy-associated malaria (PAM) is a severe form of the disease caused by sequestration of Plasmodium falciparum-infected red blood cells (iRBCs) in the developing placenta. Pathogenesis of PAM is partially based on immunopathology, with frequent monocyte infiltration into the placenta. Neutrophils are abundant blood cells that are essential for immune defence but may also cause inflammatory pathology. Their role in PAM remains unclear. We analysed neutrophil alterations in the context of PAM to better understand their contribution to disease development. Pregnant women exposed to Plasmodium falciparum had decreased numbers of circulating neutrophils. Placental-like BeWo cells stimulated with malaria parasites produced the neutrophil chemoattractant IL-8 and recruited neutrophils in a trans-well assay. Finally, immunostaining of a PAM placenta confirmed neutrophil accumulation in the intervillous space. Our data indicate neutrophils may play a role in placental malaria and should be more closely examined as an etiological agent in the pathophysiology of disease.

Influence of varus/valgus positioning of the Nanos® and Metha® short-stemmed prostheses on stress shielding of metaphyseal bone.

The aim of this study was to analyze bone remodeling around the Nanos® (Smith & Nephew) and Metha® (Aesculap AG) implants as a function of varus/valgus stem positioning. In 75 patients with diagnosed coxarthrosis, either Nanos® (n= 51) or Metha® (n= 24) prostheses were implanted. Digital assessment of plain radiographs immediately, 97 days, and 381 days after THA showed no clinically-relevant migration, angulation, or change in offset and center of rotation. The DEXA scans showed significant BMD changes in Gruen zones 1 (-12.8%), 2 (-3.3%), 6 (+6.4%), and 7(-7.8%)(t-test). The pre/postoperative CCD for the Nanos® was 129°/ 135° and for the Metha® 131°/ 127°. Linear regression analysis showed no prediction for BMD by postoperative CCD or stem type. In conclusion, there was no clinically-relevant influence on proximal femur BMD according to varus/valgus implantation of the Nanos® or Metha® prostheses.

Tissue Distribution Dynamics of Human NK Cells Inferred from Peripheral Blood Depletion Kinetics after Sphingosine-1-Phosphate Receptor Blockade.

Human natural killer (NK) cell subsets differentially distribute throughout the organism. While CD56(dim) and CD56(bright) NK cell subsets similarly reside in the bone marrow (BM), the CD56(dim) population predominantly accumulates in non-lymphoid tissues and the CD56(bright) counterpart in lymphoid tissue (LT). The dynamics with which these NK cell subsets redistribute to tissues remains unexplored. Here, we studied individuals newly exposed to fingolimod, a drug that efficiently blocks sphingosine-1-phosphate (S1P)-directed lymphocyte - including NK cell - egress from tissue to blood. During an observation period of 6h peripheral blood depletion of CD56(bright) NK cells was observed 3 h after first dose of fingolimod, with 40-50% depletion after 6 h, while a decrease of the numbers of CD56(dim) NK cells did not reach the level of statistical significance. In vitro, CD56(bright) and CD56(dim) NK cells responded comparably to the BM-homing chemokine CXCL12, while CD56(bright) NK cells migrated more efficiently in gradients of the LT-homing chemokines CCL19 and CCL21. In conjuncture with these in vitro studies, the indirectly observed subset-specific depletion kinetics from blood are compatible with preferential and more rapid redistribution of CD56(bright) NK cells from blood to peripheral tissue such as LT and possibly also the inflamed central nervous system. These data shed light on an unexplored level at which access of NK cells to LT, and thus, for example antigen-presenting cells, is regulated.

Statins selectively inhibit leukocyte function antigen-1 by binding to a novel regulatory integrin site.

The beta2 integrin leukocyte function antigen-1 (LFA-1) has an important role in the pathophysiology of inflammatory and autoimmune diseases. Here we report that statin compounds commonly used for the treatment of hypercholesterolemia selectively blocked LFA-1-mediated adhesion and costimulation of lymphocytes. This effect was unrelated to the statins' inhibition of 3-hydroxy-3-methylglutaryl coenzyme-A reductase; instead it occurred via binding to a novel allosteric site within LFA-1. Subsequent optimization of the statins for LFA-1 binding resulted in potent, selective and orally active LFA-1 inhibitors that suppress the inflammatory response in a murine model of peritonitis. Targeting of the statin-binding site of LFA-1 could be used to treat diseases such as psoriasis, rheumatoid arthritis, ischemia/reperfusion injury and transplant rejection.

Interferon alpha increases the frequency of interferon gamma-producing human CD4+ T cells.

An increased ratio of T helper type 2 (Th2)- vs Th1-like cells contributes to the immune dysregulation in allergic disease situations and in many chronic infections, including AIDS. Th2-type immune responses are characterized by Th cells that produce increased levels of interleukin-4 (IL-4) and decreased levels of interferon gamma (IFN-gamma). The induction of either a Th1- or a Th2-like phenotype may be critically controlled by the antigen-presenting cells and their cytokines, e.g., IFN-alpha. In this study we have determined the frequencies of potential IL-4- and/or IFN-gamma-producing T cells in the peripheral blood of randomly selected healthy individuals, and analyzed whether IFN-alpha controls IL-4 and/or IFN-gamma production. Purified CD4+ or CD8+ T cells were stimulated for 24 h via the T cell receptor/CD3 complex in the presence or absence of IFN-alpha, and single IL-4- and IFN-gamma-secreting cells were detected in enzyme-linked immunospot assays. In the absence of IFN-alpha, CD4 cells produced IFN-gamma at frequencies of 1:50-300, and produced IL-4 at frequencies of 1:110-<1:100,000. Addition of IFN-alpha during the activation of CD4 cells increased the levels of IFN-gamma mRNA. As a consequence, the numbers of IFN-gamma-producing CD4 cells and the amounts of secreted IFN-gamma increased 10-fold. In contrast, IFN-alpha did not increase the frequency of IL-4-secreting CD4 cells. In the absence of IFN-alpha, addition of exogenous IL-4 to cultures of CD4 cells suppressed IFN-gamma secretion by 70%. However, in the presence of IFN-alpha, IL-4 did not display any suppressive effect. Compared with CD4 cells, CD8 cells produced IFN-gamma more frequently (1:5-10) but IL-4 less frequently (1:5,300 to < 1:100,000). IFN-alpha did not display any effect on the frequency of either IFN-gamma or IL-4 production by CD8 cells. Taken together the results indicate that IFN-alpha increases the frequency of IFN-gamma-secreting CD4 Th cells and antagonizes the suppressive effect of IL-4 on IFN-gamma production. As a consequence, IFN-alpha may favor the induction and maintenance of Th1-like cells and thereby counteract Th2-driven allergic immune responses.

CC chemokine receptor 7-dependent and -independent pathways for lymphocyte homing: modulation by FTY720.

Cognate interaction of chemokine receptor CCR7 on lymphocytes with its ligands CCL19 and CCL21 expressed on high endothelial venules (HEVs) is essential for effective migration of T and B cells across HEVs into secondary lymphoid organs. Plt mice, which lack expression of CCL19 and CCL21-ser, both ligands for CCR7 on HEVs, as well as CCR7-deficient mice, have a defective cell migration and reduced homing of lymphocytes. FTY720, a novel immunosuppressant, causes a reduction of lymphocytes in peripheral blood and tissues and their sequestration into lymphoid tissues. In this study we demonstrate that FTY720 rescues the homing defect in both CCR7(-/-) mice and plt mice. After FTY720 treatment, the number of CD4(+) and CD8(+) T cells as well as B cells in peripheral blood is reduced while pertussis toxin-sensitive homing into peripheral lymph nodes, mesenteric lymph node, and Peyer's patches is increased. Immunohistology demonstrates that FTY720 enables these cells to enter lymphoid tissue through HEVs. Thus, our data suggest an alternative G-alpha(i)-dependent, CCR7-CCL19/CCL21-independent mechanism for lymphocyte homing through HEVs which is strongly augmented in the presence of FTY720.

Requirement for beta-catenin in anterior-posterior axis formation in mice.

The anterior-posterior axis of the mouse embryo is defined before formation of the primitive streak, and axis specification and subsequent anterior development involves signaling from both embryonic ectoderm and visceral endoderm. Tauhe Wnt signaling pathway is essential for various developmental processes, but a role in anterior-posterior axis formation in the mouse has not been previously established. Beta-catenin is a central player in the Wnt pathway and in cadherin-mediated cell adhesion. We generated beta-catenin-deficient mouse embryos and observed a defect in anterior-posterior axis formation at embryonic day 5.5, as visualized by the absence of Hex and Hesx1 and the mislocation of cerberus-like and Lim1 expression. Subsequently, no mesoderm and head structures are generated. Intercellular adhesion is maintained since plakoglobin substitutes for beta-catenin. Our data demonstrate that beta-catenin function is essential in anterior-posterior axis formation in the mouse, and experiments with chimeric embryos show that this function is required in the embryonic ectoderm.

Hepatocyte growth factor/scatter factor induces a variety of tissue-specific morphogenic programs in epithelial cells.

Hepatocyte growth factor/scatter factor (HGF/SF) is the mesenchymal ligand of the epithelial tyrosine kinase receptor c-Met. In vitro, HGF/SF has morphogenic properties, e.g., induces kidney epithelial cells to form branching ducts in collagen gels. Mutation of the HGF/SF gene in mice results in embryonic lethality due to severe liver and placenta defects. Here, we have evaluated the morphogenic activity of HGF/SF with a large variety of epithelial cells grown in three-dimensional collagen matrices. We found that HGF/SF induces SW 1222 colon carcinoma cells to form crypt-like structures. In these organoids, cells exhibit apical/basolateral polarity and build a well-developed brush border towards the lumen. Capan 2 pancreas carcinoma cells, upon addition of HGF/SF, develop large hollow spheroids lined with a tight layer of polarized cells. Collagen inside the cysts is digested and the cells show features of pancreatic ducts. HGF/SF induces EpH4 mammary epithelial cells to form long branches with end-buds that resemble developing mammary ducts. pRNS-1-1 prostate epithelial cells in the presence of HGF/SF develop long ducts with distal branching as found in the prostate. Finally, HGF/SF simulates alveolar differentiation in LX-1 lung carcinoma cells. Expression of transfected HGF/SF cDNA in LX-1 lung carcinoma and EpH4 mammary epithelial cells induce morphogenesis in an autocrine manner. In the cell lines tested, HGF/SF activated the Met receptor by phosphorylation of tyrosine residues. These data show that HGF/SF induces intrinsic, tissue-specific morphogenic activities in a wide variety of epithelial cells. Apparently, HGF/SF triggers respective endogenous programs and is thus an inductive, not an instructive, mesenchymal effector for epithelial morphogenesis.

Reconstitution of mammary gland development in vitro: requirement of c-met and c-erbB2 signaling for branching and alveolar morphogenesis.

We have established a cell culture system that reproduces morphogenic processes in the developing mammary gland. EpH4 mouse mammary epithelial cells cultured in matrigel form branched tubules in the presence of hepatocyte growth factor/scatter factor (HGF/SF), the ligand of the c-met tyrosine kinase receptor. In contrast, alveolar structures are formed in the presence of neuregulin, a ligand of c-erbB tyrosine kinase receptors. These distinct morphogenic responses can also be observed with selected human mammary carcinoma tissue in explant culture. HGF/SF-induced branching was abrogated by the PI3 kinase inhibitors wortmannin and LY294002. In contrast, neuregulin- induced alveolar morphogenesis was inhibited by the MAPK kinase inhibitor PD98059. The c-met-mediated response could also be evoked by transfection of a c-met specific substrate, Gab1, which can activate the PI3 kinase pathway. An activated hybrid receptor that contained the intracellular domain of c-erbB2 receptor suffices to induce alveolar morphogenesis, and was observed in the presence of tyrosine residues Y1028, Y1144, Y1201, and Y1226/27 in the substrate-binding domain of c-erbB2. Our data demonstrate that c-met and c-erbB2 signaling elicit distinct morphogenic programs in mammary epithelial cells: formation of branched tubules relies on a pathway involving PI3 kinase, whereas alveolar morphogenesis requires MAPK kinase.

Motogenic and morphogenic activity of epithelial receptor tyrosine kinases.

Receptor tyrosine kinases play essential roles in morphogenesis and differentiation of epithelia. Here we examined various tyrosine kinase receptors, which are preferentially expressed in epithelia (c-met, c-ros, c-neu, and the keratin growth factor [KGF] receptor), for their capacity to induce cell motility and branching morphogenesis of epithelial cells. We exchanged the ligand-binding domain of these receptors by the ectodomain of trkA and could thus control signaling by the new ligand, NGF. We demonstrate here that the tyrosine kinases of c-met, c-ros, c-neu, the KGF receptor, and trkA, but not the insulin receptor, induced scattering and increased motility of kidney epithelial cells in tissue culture. Mutational analysis suggests that SHC binding is essential for scattering and increased cell motility induced by trkA. The induction of motility in epithelial cells is thus an important feature of various receptor tyrosine kinases, which in vivo play a role in embryogenesis and metastasis. In contrast, only the c-met receptor promoted branching morphogenesis of kidney epithelial cells in three-dimensional matrices, which resemble the formation of tubular epithelia in development. Interestingly, the ability of c-met to induce morphogenesis could be transferred to trkA, when in a novel receptor hybrid COOH-terminal sequences of c-met (including Y14 to Y16) were fused to the trkA kinase domain. These data demonstrate that tubulogenesis of epithelia is a restricted activity of tyrosine kinases, as yet only demonstrated for the c-met receptor. We predict the existence of specific substrates that mediate this morphogenesis signal.

Targeted mutation of plakoglobin in mice reveals essential functions of desmosomes in the embryonic heart.

Plakoglobin (gamma-catenin), a member of the armadillo family of proteins, is a constituent of the cytoplasmic plaque of desmosomes as well as of other adhering cell junctions, and is involved in anchorage of cytoskeletal filaments to specific cadherins. We have generated a null mutation of the plakoglobin gene in mice. Homozygous -/- mutant animals die between days 12-16 of embryogenesis due to defects in heart function. Often, heart ventricles burst and blood floods the pericard. This tissue instability correlates with the absence of desmosomes in heart, but not in epithelia organs. Instead, extended adherens junctions are formed in the heart, which contain desmosomal proteins, i.e., desmoplakin. Thus, plakoglobin is an essential component of myocardiac desmosomes and seems to play a crucial role in the sorting out of desmosomal and adherens junction components, and consequently in the architecture of intercalated discs and the stabilization of heart tissue.

Analysis of sphingosine 1-phosphate receptors involved in constriction of isolated cerebral arteries with receptor null mice and pharmacological tools.

BACKGROUND AND PURPOSE: Sphingosine 1-phosphate (S1P) selectively and potently constricts isolated cerebral arteries, but this response has not been pharmacologically characterized. EXPERIMENTAL APPROACH: The receptor subtype(s) involved in S1P-induced cerebrovascular constriction were characterized using genetic (S1P(2) and S1P(3) receptor null mice) and pharmacological tools (phospho-FTY720, a S1P(1/3/4/5) receptor agonist; SEW2871, a S1P(1) receptor agonist, JTE-013, a S1P(2) receptor antagonist, VPC23019, a S1P(1/3) receptor antagonist). Isolated basilar or peripheral (femoral, mesenteric resistance) arteries, from either rat or mouse, were studied in a wire myograph. KEY RESULTS: S1P concentration-dependently constricted basilar artery in rat, wild-type (WT) and S1P(2) null mice, but barely affected vascular tone in S1P(3) null mice. Vasoconstriction to U46619 (a thromboxane analogue) or to endothelin-1 did not differ between WT, S1P(2) and S1P(3) null mice. JTE-013 inhibited not only S1P-induced vasoconstriction, but also KCl-, U46619- and endothelin-1-induced constriction. This effect was observed in WT as well as in S1P(2) null mice. VPC23019 increased the concentration-dependent vasoconstriction to S1P in both rat and mouse basilar arteries with intact endothelium, but not in rat basilar artery without endothelium. Phospho-FTY720 concentration-dependently constricted rat basilar arteries, but not femoral or mesenteric resistance arteries, while SEW2871 did not induce any response in the same arteries. CONCLUSIONS AND IMPLICATIONS: S1P constricts cerebral arteries through S1P(3) receptors. The purported S1P(2) receptor antagonist JTE-013 does not appear to be selective, at least in rodents. Enhancement of S1P-induced contraction by VPC23019 might be related to blockade of S1P(1) receptors and NO generation.

Non-competitive resource exploitation within mosquito shapes within-host malaria infectivity and virulence.

Malaria is a fatal human parasitic disease transmitted by a mosquito vector. Although the evolution of within-host malaria virulence has been the focus of many theoretical and empirical studies, the vector's contribution to this process is not well understood. Here, we explore how within-vector resource exploitation would impact the evolution of within-host Plasmodium virulence. By combining within-vector dynamics and malaria epidemiology, we develop a mathematical model, which predicts that non-competitive parasitic resource exploitation within-vector restricts within-host parasite virulence. To validate our model, we experimentally manipulate mosquito lipid trafficking and gauge within-vector parasite development and within-host infectivity and virulence. We find that mosquito-derived lipids determine within-host parasite virulence by shaping development (quantity) and metabolic activity (quality) of transmissible sporozoites. Our findings uncover the potential impact of within-vector environment and vector control strategies on the evolution of malaria virulence.

Mammalian homologues of C. elegans PAR-1 are asymmetrically localized in epithelial cells and may influence their polarity.

The establishment of polarity in the embryo is fundamental for the correct development of an organism [1]. The first cleavage of the Caenorhabditis elegans embryo is asymmetric with certain cytoplasmic components being distributed unequally between the daughter cells [2-4]. Using a genetic screen, Kemphues and co-workers have identified six par genes (partition-defective) [5,6], which are involved in the process of asymmetric division. One of these genes encodes a highly conserved protein, PAR-1, which is a serine/threonine kinase that localizes asymmetrically to the posterior part of the zygote and to those blastocysts that give rise to the germ line [7-9]. We reasoned that the mammalian homologue of PAR-1 (mPAR-1) might be involved in the process of polarization of epithelial cells, which consist of apical and basolateral membrane domains. We found that mPAR-1 was expressed in a wide variety of epithelial tissues and cell lines and was associated with the cellular cortex. In polarized epithelial cells, mPAR-1 was asymmetrically localized to the lateral domain. A fusion protein lacking the kinase domain had the same localization as the full-length protein but its prolonged expression acted in a dominant-negative fashion: lateral adhesion of the transfected cells to neighbouring cells was diminished, resulting in the former cells being 'squeezed out' from the monolayer. Moreover, the polarity of these cells was disturbed resulting in mislocalization of E-cadherin. Thus, in the C. elegans embryo and in epithelial cells, polarity appears to be governed by similar mechanisms.

Engineered mutants of HGF/SF with reduced binding to heparan sulphate proteoglycans, decreased clearance and enhanced activity in vivo.

BACKGROUND: Although a number of growth factors bind cell-surface heparan sulphate proteoglycans (HSPGs), the role of this interaction is unclear except for fibroblast growth factor which requires HSPG binding for signalling. Hepatocyte growth factor/scatter factor (HGF/SF) plays important roles in mammalian development and tissue regeneration and acts on target cells through a specific receptor tyrosine kinase encoded by the c-met proto-oncogene. This factor also binds HSPGs with high affinity, but conflicting data have been reported on the role of HSPG binding in HGF/SF signalling. RESULTS: To map the binding sites for HSPG and the Met receptor in HGF/SF, we have engineered a number of HGF/SF mutants in which several clusters of solvent-accessible residues in the hairpin structure of the amino-terminal domain or in kringle 2 have been replaced. Two of the mutants (HP1 and HP2) showed greatly decreased (more than 50-fold) affinity for heparin and HSPGs but retained full mitogenic and motogenic activities on target cells in culture. Furthermore, when compared with wild-type HGF/SF, the HP1 mutant exhibited a delayed clearance from the blood, higher tissue levels and a higher induction of DNA synthesis in normal, adult murine liver. CONCLUSIONS: These results establish the following: the binding sites in HGF/SF for Met and for HSPGs can be dissociated by protein engineering; high-affinity binding of HGF/SF to HSPGs is not essential for signalling; one role of HSPG binding in the HGF/SF system appears to be sequestration and degradation of the growth factor; and HGF/SF mutants with decreased affinity for HSPGs exhibit enhanced activity in vivo.

Role of morphogenetic factors in metastasis of mammary carcinoma cells.

We have analysed the role of the morphogenetic factors hepatocyte growth factor/scatter factor (HGF), neuregulin and E-cadherin in the process of metastasis and morphogenesis of mammary carcinoma cells. The cDNAs for HGF, neuregulin and E-cadherin were stably expressed in anaplastic human MDA MB 435 carcinoma cells. The altered cells were then injected into the mammary fat pads of nude mice, where they form tumors which can spontaneously metastasize to the lungs. We found that expression of HGF or neuregulin promoted metastasis whereas expression of the cell adhesion molecule E-cadherin was inhibitory. Moreover, expression of E-cadherin reconstituted the ability of the cells to form morphogenetic structures in matrigel cultures in response to HGF. These data demonstrate that HGF and neuregulin, which control branching or lobulo-alveolar morphogenesis of normal breast epithelium, do have metastasis-promoting effects on breast carcinoma cells. Moreover, our results suggest that the differential activities of the two factors can be explained by the degree of epithelial differentiation: induction of morphogenesis requires an intact epithelial adhesion and differentiation system, whereas induction of metastasis is observed when the cells have lost their epithelial characteristics.

Control of intestinal allograft rejection by FTY720 and costimulation blockade.

INTRODUCTION: The clinical application of small bowel transplantation (SBTx) is hampered by its pronounced immunogenicity. In this study we examined the effects of the novel immunosuppressant FTY720 and costimulation blockade by an anti-CD40L mAb (MR-1) in a stringent mouse model of SBTx. METHODS: SBTx was performed in mice with a full MHC mismatch (donors: C3H=H-2(k); recipients: C57BL/6=H-2(b)). Recipients were divided into four groups: 1, untreated group; 2, MR1 monotherapy (500 microg IV on days 0, 2, 4, and 7); 3, FTY720 monotherapy (1 mg/kg body weight PO for 14 consecutive days after transplantation); 4, FTY720 plus MR1-treated group. Graft rejection grades were assessed by H&E staining. Graft mesenteric lymph nodes (MLNs), Peyer's patches (PPs), as well as intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LPLs) were analyzed by flow cytometry and three-color immunofluorescence staining. RESULTS: Neither FTY720 nor MR1 monotherapy was efficient in preventing the rejection of mouse intestinal allografts, whereas FTY720 plus MR1 profoundly inhibited the rejection response at the 14th posttransplant day. The infiltration of host lymphocytes was reduced in graft MLNs, PPs, IELs, and LPLs by FTY720 therapy. FTY720 plus MR1 inhibited host CD8(+) T-cell infiltration in graft LPLs when compared with grafts treated with FTY720 only. Additionally, two subpopulations, CD11b(+high) Gr1(-) and CD11b(+intermediate) Gr1(+) cells, were decreased in FTY720-treated grafts. CONCLUSIONS: FTY720 plus MR1 efficiently delayed intestinal allograft rejection in a mouse model by preventing the infiltration of host lymphocytes, particularly of CD8(+) cells.

FTY720 inhibits TH1-mediated allogeneic humoral immune response.

Phosphorylated FTY720 is an analog of Sphingosine 1 Phosphate (S1P) with immunosuppressive activity that negatively regulates the expression of S1P-Receptor 1. It also inhibits the migration of CD4 and CD8 single-positive T cells from the thymus to the periphery, sequesters peripheral blood lymphocytes in lymph nodes and Peyer's patches, and delays the exit of effector T cells toward the graft. The aim of our work was to study the effect of FTY720 on the kinetics of skin allograft rejection in a fully mismatched model; euthymic (Euthy) versus thymectomized (ATX) C57BL/6 mice (haplotype H-2(b)) recipients of BALB/c mice (haplotype H-2(d)) donor cells. The animals were injected daily with FTY720 (1 mg/kg) intraperitoneally for 2 weeks. To monitor the humoral immune response, serum samples collected at day 0 (pre-immune) and at day 23 after skin graft rejection were examined using BALB/c thymocytes as antigens in flow cytometry. To confirm the effect of FTY720 on peripheral lymphocytes, peripheral blood was analyzed by flow cytometry. Euthy and ATX FTY720-treated mice showed prolongation of skin allograft survival when compared with nontreated Euthy and ATX controls (P < .005). Unexpectedly, FTY720-treated Euthy mice showed significantly delayed graft rejection when compared to similarly treated ATX mice (P < .005). The delayed graft rejection in FTY720-treated Euthy mice correlated with a reduced content of Th1-mediated IgG(2a) and IgG(2b) antibodies when compared with FTY720-treated ATX mice (P < .05). In conclusion, FTY720 delays the kinetics of allograft rejection in a fully mismatched model by inhibiting Th1-mediated humoral immune responses. The presence of the host thymus appears to be required for this phenomenon.

T cell dependent differentiation of human B cells: direct switch from IgM to IgE, and sequential switch from IgM via IgG to IgA production.

Ig production by splenic human B cells that express different surface Ig isotypes were analysed in limiting dilution cultures. Therefore, FACS sorted IgM+, IgG+ and IgA1+ B cells were stimulated with PMA-activated EL4 thymoma cells as helper cells in the presence of IL-2 and IL-4. We found that at least every second B cell responded in vitro and secreted the antibody corresponding to its surface Ig isotype. IgE secreting cells developed from surface IgM+ D+ cells (1/31 to 1/167), but not from IgG+ or IgA1+ cells (much less than 1/5000). Negative signalling of the IgM+ B cells by addition of anti-IgM antibodies into the cultures reduced the number of single IgM producing cells by greater than 85%, and completely inhibited IgE switch. In contrast, anti-IgG and anti-IgA antibodies did not reduce the IgE response. The results indicate a direct switch from IgM to IgE secretion in vitro. In contrast to IgE, IgA secreting cells developed from IgM+D+ (1/30 to 1/51) and from IgG+ B cells (1/14 to 1/25). Negative signalling of the IgG+ B cell subset within total B cells by anti-IgG antibodies suppressed the development of IgG as well as IgA producing cells, but did not inhibit IgM and IgE responses. This indicates a sequential switch from IgM via IgG to IgA. Taken together, this study indicates that IgE secreting cells are derived directly from IgM+D+ B cells by non-sequential switching, whereas IgA producing cells preferentially develop by sequential switching via IgG+ B cells.

Vaccination of mice with the protective F3G3 antigen of Toxoplasma gondii activates CD4+ but not CD8+ T cells and induces Toxoplasma specific IgG antibody.

A major cytoplasmic Toxoplasma gondii (T. gondii) antigen recognized by monoclonal antibody F3G3 (F3G3-Ag), as well as two surface antigens recognized by monoclonal antibodies 2G11 and 1E11 respectively (2G11-Ag; 1E11-Ag), were isolated from crude Toxoplasma sonicates using affinity chromatography. Purified F3G3-Ag induced long term protection against Toxoplasma infection in mice and induced Toxoplasma specific IgG antibody. CD4+ but not CD8+ T cells from immune animals proliferated and produced IL-2 upon restimulation with either Toxoplasma sonicate or F3G3-Ag in vitro. Furthermore, CD4+ T cells from mice immunized with F3G3-Ag responded to purified 2G11- and 1E11-Ag. In contrast, CD4+ T cells from mice immunized with 2G11-Ag responded to Toxoplasma sonicate and 2G11-Ag, but not to F3G3- or 1E11-Ag. The results may indicate that the protective F3G3-Ag shares immunogenic epitopes present also on 2G11- and 1E11-Ag, since the F3G3-Ag used for the vaccination did not contain detectable amounts of 2G11- or 1E11-Ag, and none of the antigens displayed any mitogenicity. Taken together the results show that the cytoplasmic F3G3-Ag of T. gondii induces CD4+ T helper cells, Toxoplasma specific IgG antibodies and long term protection against Toxoplasma infection, but does not induce detectable sensitization of the CD8+ T cell compartment.