Murine IgM Research Articles

Proximity-Based Labeling Identifies MHC Class II and CD37 as B Cell Receptor-Proximal Proteins with Immunological Functions.

The BCR allows for Ag-driven B cell activation and subsequent Ag endocytosis, processing, and presentation to recruit T cell help. Core drivers of BCR signaling and endocytosis are motifs within the receptor's cytoplasmic tail (primarily CD79). However, BCR function can be tuned by other proximal cellular elements, such as CD20 and membrane lipid microdomains. To identify additional proteins that could modulate BCR function, we used a proximity-based biotinylation technique paired with mass spectrometry to identify molecular neighbors of the murine IgM BCR. Those neighbors include MHC class II molecules, integrins, various transporters, and membrane microdomain proteins. Class II molecules, some of which are invariant chain-associated nascent class II, are a readily detected BCR neighbor. This finding is consistent with reports of BCR-class II association within intracellular compartments. The BCR is also in close proximity to multiple proteins involved in the formation of membrane microdomains, including CD37, raftlin, and Ig superfamily member 8. Known defects in T cell-dependent humoral immunity in CD37 knockout mice suggest a role for CD37 in BCR function. In line with this notion, CRISPR-based knockout of CD37 expression in a B cell line heightens BCR signaling, slows BCR endocytosis, and tempers formation of peptide-class II complexes. These results indicate that BCR molecular neighbors can impact membrane-mediated BCR functions. Overall, a proximity-based labeling technique allowed for identification of multiple previously unknown BCR molecular neighbors, including the tetraspanin protein CD37, which can modulate BCR function.

Hindlimb unloading, a physiological model of microgravity, modifies the murine bone marrow IgM repertoire in a similar manner as aging but less strongly

BackgroundThe spaceflight environment is an extreme environment that affects the immune system of approximately 50% of astronauts. With planned long-duration missions, such as the deployment of the Lunar Gateway and possible interplanetary missions, it is mandatory to determine how all components of the immune system are affected, which will allow the establishment of countermeasures to preserve astronaut health. However, despite being an important component of the immune system, antibody-mediated humoral immunity has rarely been investigated in the context of the effects of the space environment. It has previously been demonstrated that 30 days aboard the BION-M1 satellite and 21 days of hindlimb unloading (HU), a model classically used to mimic the effects of microgravity, decrease murine B lymphopoiesis. Furthermore, modifications in B lymphopoiesis reported in young mice subjected to 21 days of HU were shown to be similar to those observed in aged mice (18–22 months). Since the primary antibody repertoire composed of IgM is created by V(D) J recombination during B lymphopoiesis, the objective of this study was to assess the degree of similarity between changes in the bone marrow IgM repertoire and in the V(D)J recombination process in 2.5-month-old mice subjected to 21 days of HU and aged (18 months) mice.ResultsWe found that in 21 days, HU induced changes in the IgM repertoire that were approximately 3-fold less than those in aged mice, which is a rapid effect. Bone remodeling and epigenetics likely mediate these changes. Indeed, we previously demonstrated a significant decrease in tibial morphometric parameters from day 6 of HU and a progressive reduction in these parameters until day 21 of HU, and it has been shown that age and microgravity induce epigenetic changes.ConclusionThese data reveal novel immune changes that are akin to advanced aging and underline the importance of studying the effects of spaceflight on antibody-mediated humoral immunity.

Mice possess a more limited natural antihuman factor VIII antibody repertoire than humans that is produced disproportionately by marginal zone B cells

BackgroundOne-third of patients with severe hemophilia A develop neutralizing antibodies to the factor VIII (FVIII) protein in response to intravenous replacement therapy. Patients may also generate natural, nonneutralizing antibodies to FVIII before FVIII exposure. These patients are at increased risk of developing neutralizing antibodies to FVIII. However, natural anti-FVIII antibodies are also present in healthy human donors. ObjectivesTo further characterize the natural antihuman (h) FVIII antibody repertoire in mice and humans. MethodsAn in-house ELISA was developed using a purified polyclonal immunoglobulin (Ig) standard to quantify anti-hFVIII Ig in cell culture supernatant or plasma from mice (wild-type and FVIII-/-) and adult human donors. ResultsAll naïve wild-type and FVIII-/- mice, as well as healthy human donors, possess natural anti-hFVIII antibodies. Mice only have natural anti-hFVIII IgM, which is present in germ-free mice, suggesting that they are germline encoded. Although murine marginal zone B cells (MZBs) contribute 44% to all circulating natural IgM, they contribute disproportionately to the anti-hFVIII IgM repertoire (82%). This naturally occurring murine MZB-derived IgM is not B-domain specific and is reduced by intravenously administered hFVIII, suggesting that it may form immune complexes immediately upon hFVIII administration. Natural anti-hFVIII antibodies of IgG, IgM, and IgA isotypes can be detected in adult human donors. There were increased levels of B-domain-favoring anti-hFVIII IgG in 14% of healthy donors, which were markedly different from the rest of the “low-titer” population. ConclusionsThere is a preponderance of natural anti-hFVIII antibodies in both mice and healthy adult human donors.

Abstract 12366: Intracoronary Delivery of E06 Antibody Directed to Oxidized Phospholipids Decreases Infarct Size in a Porcine Model of Ischemia/Reperfusion Injury

Introduction: Myocardial ischemia/reperfusion injury (IRI) results in additional myocardial cell loss post reperfusion. Oxidized phosphocholine(PC)-containing phospholipids (OxPL) have been shown to result in cardiomyocyte cell death during IRI. E06 is a natural murine monoclonal IgM antibody which binds to the PC headgroup of OxPL. Transgenic mice expressing a single-chain Fv E06 fragment have recently been shown to have smaller infarct sizes post myocardial IRI. The objective of this study was to determine if directly infused E06 IgM reduced IRI in a porcine model of reperfusion injury that more closely reflects human physiology. Methods: Male pigs, 45 to 50 kg, were randomized equally to IRI in two groups: 1) control with saline coronary infusion (n=7). 2) IgM E06 coronary infusion over 1 hour (n=7). The left anterior descending (LAD) artery was occluded distal to the second diagonal branch for 60 minutes using an angioplasty balloon. Following balloon deflation, saline or IgM E06 was infused over 60 min through a microcatheter. Following 120 min of total reperfusion, the area at risk (AAR) and infarct size (IS) were determined by triphenyltetrazolium chloride staining technique (TTC), and myocardial salvage index determined. Results: All animals survived post reperfusion and no differences were present in hemodynamics at the baseline and 2 h post reperfusion between groups. A 51.3% reduction in infarct size was noted in animals receiving intracoronary E06 compared to controls (IS/AAR 21.7% ± 3.4 vs 42.3% ± 3.7 p<0.0005). IS/LV size (7.7 ± 3.2 vs 11.9 ± 1.2 p<0.004) and myocardial salvage index (82.6% vs 57.6% in controls) were significantly improved in animals receiving E06 compared to controls. Conclusion: Intracoronary delivery of E06 antibody at the time of reperfusion leads to a significant reduction in infarct size, suggesting that generation of OxPL during reperfusion leads to cardiomyocyte cell death. Translation of this approach using humanized anti-OxPL antibodies may allow a novel approach to treat myocardial IRI in humans.

CD75s Represents a Therapeutic Target for Antibody-Based Immunotherapy of B Cell Lymphoma and Multiple Myeloma

Recently, with Daratumumab and Elotuzumab two monoclonal antibodies targeting malignant plasma cells have been approved. Despite convincing clinical activity, still not all patients benefit and novel well-defined surface receptors with an expression profile restricted to mature B cells may represent promising target structures. A monoclonal antibody designated EBU-141 was generated in our laboratory and targets CD75s. The antibody is of mouse IgM isotype and reacts with mature B- cells as well as plasma cells. Of note, EBU-141 specifically binds to myeloma/plasma cell leukemia cells and B cell lymphomas, including Burkitt's lymphoma and CLL, while no binding to precursor B-cell leukemias was found. Non-B-lineage hematolymphatic tumors showed no significant staining with EBU-141. The aim of the present study was to investigate effector mechanisms mediated by EBU-141 and to develop therapeutically useful EBU-141-based chimeric antibody variants. The potential of these different formats for immunotherapy of B cell lymphomas and multiple myeloma was evaluated.The variable regions of EBU-141 were isolated and a chimeric IgG1k antibody called chEBU-141 was generated. chEBU-141 was produced by transient transfection and purified from cell culture supernatants by affinity chromatography. To investigate the antibodies' direct inhibitory effects and Fc-mediated modes of action, cell proliferation assays and chromium release experiments with myeloma and lymphoma cell lines were performed. The parentalhybridoma antibody EBU-141 significantly induced programmed cell death by cross-linking the target antigen on the cell surface of lymphoma cells. It also triggered strong complement-dependent cytotoxicity (CDC) against lymphoma cells using human serum as source of complement. Interestingly, EBU-141 was not capable in triggering CDC against myeloma cell lines and patient-derived malignant plasma cells despite significant expression of CD75s. When compared with the IgM antibody EBU-141, the bivalent IgG1 chEBU-141 lacked CDC activity. In contrast, chEBU-141 was capable to trigger potent antibody-dependent cell-mediated cytotoxicity (ADCC) against lymphoma and myeloma cells using human mononuclear cells or isolated NK cells as effector cells.Here, CD75s could be identified as a promising target for immunotherapy of mature B cell malignancies. The selection of the chimeric IgG1 variant chEBU-141 allows especially effective triggering of ADCC. The potential of CD75s antibody therapy may be further improved by applying Fc-engineering technologies that enhance CDC activity, an effector function potently triggered by the murine IgM antibody. DisclosuresKlausz:Affimed: Research Funding. Kellner:Affimed: Research Funding. Peipp:Affimed: Research Funding.

Sialic Acid Protects Nontypeable Haemophilus influenzae from Natural IgM and Promotes Survival in Murine Respiratory Tract.

Nontypeable Haemophilus influenzae (NTHi), a common inhabitant of the human nasopharynx and upper airways, causes opportunistic respiratory tract infections that are frequently recurring and chronic. NTHi utilizes sialic acid from the host to evade antibacterial defenses and persist in mucosal tissues; however, the role of sialic acid scavenged by NTHi during infection is not fully understood. We previously showed that sialylation protects specific epitopes on NTHi lipooligosaccharide (LOS) targeted by bactericidal IgM in normal human serum. Here, we evaluated the importance of immune evasion mediated by LOS sialylation in the mouse respiratory tract using wild-type H. influenzae and an isogenic siaB mutant incapable of sialylating the LOS. Sialylation protected common NTHi glycan structures recognized by human and murine IgM and protected NTHi from complement-mediated killing directed by IgM against these structures. Protection from IgM binding by sialylated LOS correlated with decreased survival of the siaB mutant versus the wild type in the murine lung. Complement depletion with cobra venom factor increased survival of the siaB mutant in the nasopharynx but not in the lungs, suggesting differing roles of sialylation at these sites. Prior infection increased IgM against H. influenzae but not against sialic acid-protected epitopes, consistent with sialic acid-mediated immune evasion during infection. These results provide mechanistic insight into an NTHi evasive strategy against an immune defense conserved across host species, highlighting the potential of the mouse model for development of anti-infective strategies targeting LOS antigens of NTHi.

Application of printable antibody ink for solid-phase immobilization of ABO antibody using photoactive hydrogel for surface plasmon resonance imaging

Biochips for multiplex blood typing through surface plasmon resonance imaging (SPRi) readout have been previously reported based on arrays of red blood cell (RBC) specific ABO antibodies (Abs). Although conventional surfaces, such as CM-dextran, are robust and highly specific, they are time and labor intensive to generate and functionalize. This work investigates the fabrication parameters and performance of printable ink consisting of a photoactive hydrogel precursor and antibody mixture for the fabrication of SPRi array biochip. The solid-phase immobilization of commercially available murine IgM ABO Abs on a SPR sensor chip with a multiplex detection of ABO antigens present on the surface membrane of human RBCs is reported. A quick and simple solid phase immobilization of protein on a SPR sensor chip was attained using the photocrosslinking polymer and microarray printing platform. A high density immobilized probes is obtained which allows high sensitivity, specificity, and surface regeneration. A signal to noise ratio of 22:1 and 25:1 at 5% and 10% immobilized-Ab respectively, is obtained with 5% RBC concentration. The sensor surface can be successfully regenerated for repeated use using DI water. Without loss of function, the Ab-printed chips could be stored up to 3 weeks at 4 °C.

Erratum to: Identification of Tn antigen O-GalNAc-expressing glycoproteins in human carcinomas using novel anti-Tn recombinant antibodies.

The Tn antigen is a neoantigen abnormally expressed in many human carcinomas and expression correlates with metastasis and poor survival. To explore its biomarker potential, new antibodies are needed that specifically recognize this antigen in tumors. Here we generated two recombinant antibodies to the Tn antigen, Remab6 as a chimeric human IgG1 antibody and ReBaGs6 as a murine IgM antibody and characterized their specificities using multiple biochemical and biological approaches. Both Remab6 and ReBaGs6 recognize clustered Tn structures, but most importantly do not recognize glycoforms of human IgA1 that contain potential cross-reactive Tn antigen structures. In flow cytometry and immunofluorescence analyses, Remab6 recognizes human cancer cell lines expressing the Tn antigen, but not their Tn-negative counterparts. In immunohistochemistry (IHC), Remab6 stains many human cancers in tissue array format but rarely stains normal tissues and then mostly intracellularly. We used these antibodies to identify several unique Tn-containing glycoproteins in Tn-positive Colo205 cells, indicating their utility for glycoproteomics in future biomarker studies. Thus, recombinant Remab6 and ReBaGs6 are useful for biochemical characterization of cancer cells and IHC of tumors and represent promising tools for Tn biomarker discovery independently of recognition of IgA1.

Identification of Tn antigen O-GalNAc-expressing glycoproteins in human carcinomas using novel anti-Tn recombinant antibodies.

The Tn antigen is a neoantigen abnormally expressed in many human carcinomas and expression correlates with metastasis and poor survival. To explore its biomarker potential, new antibodies are needed that specifically recognize this antigen in tumors. Here we generated two recombinant antibodies to the Tn antigen, Remab6 as a chimeric human IgG1 antibody and ReBaGs6 as a murine IgM antibody and characterized their specificities using multiple biochemical and biological approaches. Both Remab6 and ReBaGs6 recognize clustered Tn structures, but most importantly do not recognize glycoforms of human IgA1 that contain potential cross-reactive Tn antigen structures. In flow cytometry and immunofluorescence analyses, Remab6 recognizes human cancer cell lines expressing the Tn antigen, but not their Tn-negative counterparts. In immunohistochemistry (IHC), Remab6 stains many human cancers in tissue array format but rarely stains normal tissues and then mostly intracellularly. We used these antibodies to identify several unique Tn-containing glycoproteins in Tn-positive Colo205 cells, indicating their utility for glycoproteomics in future biomarker studies. Thus, recombinant Remab6 and ReBaGs6 are useful for biochemical characterization of cancer cells and IHC of tumors and represent promising tools for Tn biomarker discovery independently of recognition of IgA1.

IgM Antibodies Can Access Cryptic Antigens Denied to IgG: Hypothesis on Novel Binding Mechanism.

Antibodies are well-known protein mediators of immunity. IgM is the primordial member and the neglected sibling of the later-evolved and more proficient IgG in regard to their therapeutic and diagnostic use. Serendipitously, however, we found a paradox: While murine IgM antibodies specific for guanosine triphosphate (GTP) were able to recognize native guanylyl antigens found in primate or rat muscle tissues by immunofluorescence assays (which mimicked the auto-antibodies from autoimmune patients to skeletal or smooth muscle), the murine and human IgG counterparts failed. The results were replicated in cell-free direct binding assays using small latex microspheres decorated densely with GTP. The IgG antibodies could bind, however, if GTP was presented more spaciously on larger particles or as a univalent hapten. Accordingly, oligomerization of GTP (30-mer) destroyed the binding of the IgG antibodies but enhanced that of the IgMs in inhibition ELISA. We reason that, contrary to current belief, IgM does not bind in a lock-and-key manner like IgG. We hypothesize that whereas the intact and rigid antigen-binding site of IgG hinders the antibody from docking with antigens that are obstructed, in IgM, the two component polypeptides of the antigen-binding site can dissociate from each other and navigate individually through obstacles like the ancestral single-polypeptide antibodies found in sharks and camelids, both components eventually re-grouping around the antigen. We further speculate that polyreactive IgMs, which enigmatically bind to more than one type of antigen, use the same modus operandi. These findings call for a re-look at the clinical potential of IgM antibodies particularly in specific areas of cancer therapy, tissue pathology and vaccine design, where IgG antibodies have failed due to target inaccessibility.

Discovery of new Toxoplasma gondii antigenic proteins using a high throughput protein microarray approach screening sera of murine model infected orally with oocysts and tissue cysts

BackgroundToxoplasma gondii is an obligate intracellular protozoan parasite that causes congenital toxoplasmosis, as well as other serious clinical presentations in immune compromised humans. The parasite has also been recently linked to behavioral diseases in humans and other mammalian hosts. New antigens are being evaluated to develop a diagnostic kit for the diagnosis of acute infection or a protective vaccine.MethodsIn this study, we have focused on the discovery of new antigenic proteins from T. gondii genomic data using a high throughput protein microarray screening. To date, microarrays containing > 2870 candidate exon products of T. gondii have been probed with sera collected from patients with toxoplasmosis. Here, the protein microarrays are probed with well-characterized serum samples from animal models administered orally with oocysts or tissue cysts. The aim was to discover the antigens that overlap in the mouse profile with human antibody profiles published previously. For this, a reactive antigen list of 240 antigens recognized by murine IgG and IgM was identified using pooled sera from orally infected mice.ResultsAnalyses of screening data have identified plenty of antigens and showed strong immunogenicity in both mouse and human antibody profiles. Among them, ROP1, GRA2, GRA3, GRA4, GRA5, GRA6, GRA7, GRA8, GRA14, MIC1, MIC2 and MAG1 have shown strong immunogenicity and used as antigen in development of vaccines or serological diagnostic assays in previous studies.ConclusionIn addition to the above findings, ROP6, MIC12, SRS29A and SRS13 have shown strong immunogenicity but have not been tested in development of a diagnostic assay or a vaccine model yet.

Structure-function analysis and therapeutic efficacy of antibodies to fungal melanin for melanoma radioimmunotherapy

Metastatic melanoma remains difficult to treat despite recent approvals of several new drugs. Recently we reported encouraging results of Phase I clinical trial of radiolabeled with 188Re murine monoclonal IgM 6D2 to melanin in patients with Stage III/IV melanoma. Subsequently we generated a novel murine IgG 8C3 to melanin. IgGs are more amenable to humanization and cGMP (current Good Manufacturing Practice) manufacturing than IgMs. We performed comparative structural analysis of melanin-binding IgM 6D2 and IgG 8C3. The therapeutic efficacy of 213Bi- and 188Re-labeled 8C3 and its comparison with anti-CTLA4 immunotherapy was performed in B16-F10 murine melanoma model. The primary structures of these antibodies revealed significant homology, with the CDRs containing a high percentage of positively charged amino acids. The 8C3 model has a negatively charged binding surface and significant number of aromatic residues in its H3 domain, suggesting that hydrophobic interactions contribute to the antibody-melanin interaction. Radiolabeled IgG 8C3 showed significant therapeutic efficacy in murine melanoma, safety towards healthy melanin-containing tissues and favorable comparison with the anti-CTLA4 antibody. We have demonstrated that antibody binding to melanin relies on both charge and hydrophobic interactions while the in vivo data supports further development of 8C3 IgG as radioimmunotherapy reagent for metastatic melanoma.

Abolishment of proximal tubule albumin endocytosis does not affect plasma albumin during nephrotic syndrome in mice

The megalin/cubilin receptor complex is required for proximal tubular endocytosis and degradation of filtered albumin. An additional high-capacity retrieval pathway of intact albumin for the recovery of large amounts of filtered albumin has been proposed, possibly involving cooperation between megalin/cubilin and the neonatal Fc receptor. To clarify the potential role of such a pathway, we examined the effects of megalin/cubilin gene inactivation on tubular albumin uptake and plasma albumin levels in nephrotic, podocin knockout mice. Immunofluorescence microscopy of megalin/cubilin/podocin knockout mouse kidneys demonstrated abolishment of proximal tubule albumin uptake, in contrast to the excessive albumin accumulation observed in podocin knockout mice compared to controls. Correspondingly, urinary albumin excretion was increased 1.4 fold in megalin/cubilin/podocin compared to podocin knockout mice (albumin/creatinine: 226 vs. 157 mg/mg). However, no difference in plasma albumin levels was observed between megalin/cubilin/podocin and podocin knockout mice, as both were reduced to approximately 40% of controls. There were no differences in liver albumin synthesis by mRNA levels and protein abundance. Thus, megalin/cubilin knockout efficiently blocks proximal tubular albumin uptake in nephrotic mice but plasma albumin levels did not differ as a result of megalin/cubilin-deficiency, suggesting no significance of the megalin/cubilin-pathway for albumin homeostasis by retrieval of intact albumin.

IL-10 production in murine IgM+ CD138hi cells is driven by Blimp-1 and downregulated in class-switched cells.

In contrast to antibody-induced inflammatory responses, some B-cell subpopulations suppress inflammation through the production of interleukin (IL)-10. However, the mechanisms underlying Il10 gene expression during B-cell development is elusive. Here, we identify IgM+ B220lo CD138hi cells responsible for marked IL-10 production in the bone marrow and spleen of mice. These murine IL-10-producing cells predominantly secrete IgM and have unique characteristics of long-lived plasma cells in spite of high expression of surface IgM. We found that IL-10 production is strongly correlated with the expression level of Prdm1 (encoding the Blimp-1 protein), an essential regulator of plasma cell development. Furthermore, overexpression of Prdm1 induces Il10 expression in naïve B cells. Immunoglobulin class-switching recombination events resulted in the downregulation of both Il10 and Prdm1 expression in differentiating B cells. Thus, the prolonged elevation of Blimp-1 expression during the formation of IgM+ CD138hi cells without class-switching elicits IL-10 production. Adoptive transfer of Il10-deficient B cells into B-cell-deficient mice demonstrated that IgM+ CD138hi cell-derived IL-10 supports the survival of class-switched plasma cells and their antibody production in response to antigen challenge. These findings reveal an important role for IL-10 secretion by IgM+ CD138hi cells in the complete and efficient humoral response.

Radiolabeled Immunoglobulin Therapy for Patients with Solid Tumors

Purpose: To test the reactivity of monoclonal murine IgM and IgG for Tenascin-C (TNC) in formalinized solid human tumors tissue samples and to estimate the radiation dose that Yttrium- 90 labeled murine IgM reactive with TNC can deliver to a solid tumor and tumor containing draining lymph nodes. Materials and Methods: Using Immunohistochemistry (IHC), mouse anti-human TNC IgM and IgG clones were tested for the detection of TNC in formalin fixed biopsies of patients with Glioblastoma multiforme (GBM), adeno carcinoma of the exocrine pancreas (PaCa)-, breast-, colon-, renal-, ovary- prostate carcinoma, cutaneous-, ocular- melanomas, and Ewing Sarcoma. IHC was performed on all tumors with an n=1, except for PaCa and ocular melanomas, n=11. Monte-Carlo simulation and convolution calculations were used to determine the activity of Y-90 required for delivering 100Gy to a 50 × 50 × 50 mm3 water-equivalent tumor model, assuming a homogeneous distribution of the radioimmunoconjugate throughout the model volume. Results: IHC has confirmed reactivity of IgM with TNC in all of the tested human solid tumors samples except for ocular melanoma. Positive and negative controls of IgM specificity were used. The dosimetry simulation predicted an Yttrium-90 activity of 217 MBq to deliver a dose of 100Gy to the tumor model with a 6 mm sharp dose fall off in surrounding normal tissues. Conclusion: Loco-regional control of human solid tumors may be obtained with intra-tumoral administration of radiolabeled IgM targeting TNC. In TNC negative solid tumors such as ocular melanoma, other tumor-specific target(s) need to be identified.

Characterization of monoclonal antibodies generated by in vitro immunization

Abstract Monoclonal antibodies are highly valuable tools in biomedicine but the generation by hybridoma technology is very time-consuming and elaborate. In order to circumvent the consisting drawbacks an in vitro immunization approach was established by which murine as well as human monoclonal antibodies against a viral coat protein could be developed. The in vitro immunization process was performed by isolation of murine hematopoietic stem cells or human monocytes and an in vitro differentiation into immature dendritic cells. After antigen loading the cells were co-cultivated with naive T and B lymphocytes for three days in order to obtain antigen-specific B lymphocytes in culture, followed by fusion with murine myeloma cells or human/murine heteromyeloma cells. Antigen-specific hybridomas were selected and the generated antibodies were purified and characterized in this study by ELISA, western blot, gene sequencing, affinity measurements. Further the characteristics were compared to a monoclonal antibody against the same target generated by conventional hybridoma technology. Isotype detection revealed a murine IgM and a human IgG4 antibody in comparison to an IgG1 for the conventionally generated antibody. The antibodies derived from in vitro immunization showed indeed a lower affinity for the antigen as compared to the conventionally generated one, which is probably based on the significantly shorter B cell maturation (3 days) during the immunization process. Nevertheless, they were suitable for building up a sandwich based detection system. Therefore, the in vitro immunization approach seems to be a good and particularly fast alternative to conventional hybridoma technology.

Borrelia persica Infection in Immunocompetent Mice--A New Tool to Study the Infection Kinetics In Vivo.

Borrelia persica, a bacterium transmitted by the soft tick Ornithodoros tholozani, causes tick-borne relapsing fever in humans in the Middle East, Central Asia and the Indian peninsula. Immunocompetent C3H/HeOuJ mice were infected intradermally with B. persica at varying doses: 1 x 106, 1 x 104, 1 x 102 and 4 x 100 spirochetes/mouse. Subsequently, blood samples were collected and screened for the presence of B. persica DNA. Spirochetes were detected in all mice infected with 1 x 106, 1 x 104 and 1 x 102 borrelia by real-time PCR targeting the flaB gene of the bacterium. Spirochetemia developed with a one- to two-day delay when 1 x 104 and 1 x 102 borrelia were inoculated. Mice injected with only four organisms were negative in all tests. No clinical signs were observed when infected mice were compared to negative control animals. Organs (heart, spleen, urinary bladder, tarsal joint, skin and brain) were tested for B. persica-specific DNA and cultured for the detection of viable spirochetes. Compiled data show that the target organs of B. persica infections are the brain and the skin. A newly developed serological two-tiered test system (ELISA and western blot) for the detection of murine IgM, IgG and IgA antibody titers against B. persica showed a vigorous antibody response of the mice during infection. In conclusion, the infection model described here for B. persica is a platform for in vivo studies to decipher the so far unexplored survival strategies of this Borrelia species.

Natural IgM Switches the Function of Lipopolysaccharide-Activated Murine Bone Marrow-Derived Dendritic Cells to a Regulatory Dendritic Cell That Suppresses Innate Inflammation.

We have previously shown that polyclonal natural IgM protects mice from renal ischemia/reperfusion injury (IRI) by inhibiting the reperfusion inflammatory response. We hypothesized that a potential mechanism involved IgM modulation of dendritic cells (DC), as we observed high IgM binding to splenic DC. To test this hypothesis, we pretreated bone marrow-derived DC (BMDC) with polyclonal murine or human IgM prior to LPS activation and demonstrated that 0.5 × 10(6) IgM/LPS-pretreated BMDC, when injected into wild-type C57BL/6 mice 24 h before renal ischemia, protect mice from developing renal IRI. We show that this switching of LPS-activated BMDC to a regulatory phenotype requires modulation of BMDC function that is mediated by IgM binding to nonapoptotic BMDC receptors. Regulatory BMDC require IL-10 and programmed death 1 as well as downregulation of CD40 and p65 NF-κB phosphorylation to protect in renal IRI. Blocking the programmed death ligand 1 binding site just before i.v. injection of IgM/LPS-pretreated BMDC or using IL-10 knockout BMDC fails to induce protection. Similarly, IgM/LPS-pretreated BMDC are rendered nonprotective by increasing CD40 expression and phosphorylation of p65 NF-κB. How IgM/LPS regulatory BMDC suppress in vivo ischemia-induced innate inflammation remains to be determined. However, we show that suppression is dependent on other in vivo regulatory mechanisms in the host, that is, CD25(+) T cells, B cells, IL-10, and circulating IgM. There was no increase in Foxp3(+) regulatory T cells in the spleen either before or after renal IRI. Collectively, these findings show that natural IgM anti-leukocyte Abs can switch BMDC to a regulatory phenotype despite the presence of LPS that ordinarily induces BMDC maturation.

A monoclonal antibody against glycoproteins of Aspergillus fumigatus shows anti-adhesive potential

There has been an increase in the cases of fungal resistance against many antifungal drugs and an effective alternative mode in the form of immunotherapy is being considered as new hope. The adhesion of Aspergillus fumigatus conidia to the host components is one of the prime factors to cause aspergillosis. Carbohydrate components or glycoproteins present on the cell surface play an important role in interaction of the organism to the host and leads to adhesion. Any substance which is capable of disrupting this interaction may be a vital tool for the fungal clearance and hence may protect the host from infections caused by the fungus. In this study, a murine monoclonal antibody IgM generated against the secretory antigens of A. fumigatus, was found to be specific to a common epitope containing glyco-moieties of the various proteins and exhibited anti-adhesive potential in vitro.

Successful construction and massive expression of a novel Anti-CD19 human-mouse chimeric antibody Hm2E8b.

CD19 antigen is a major target for human B cell malignancies. Many studies have shown that the antibodies recognizing this antigen hold clinical therapeutic potential, while CD19 antibody of mouse origin requires genetic engineering to reduce the potential side effects of the antibody for their clinical use. There are many clones of CD19 antibodies available with different subclasses of immunoglobulin. IgM type antibody holds a high affinity and high complement activating capacities facilitating the targeting efficacy when it is used in targeting therapy. However, engineering the murine IgM antibody into a functional humanized antibody remains a challenge. The aim of this study was to construct a chimeric antibody composed of a CD19 specific murine IgM antibody 2E8 single-chain antibody fragment (scFv) and human IgG1 Fc region, which was named 2E8scFv-Fc or Hm2E8b. The function and the biological activities of this engineered antibody were characterized using a variety of approaches including cellular, immunological, flow cytometric, and molecular biological approaches. After switching from IgM- to IgG-like type antibody, Hm2E8b retained full antigen-binding activity to membrane CD19 antigen as its parental antibody 2E8, and the immune effector function analysis revealed that it could mediate complement-dependent cytotoxicity (CDC) to kill the target cells via IgG1 Fc domain. The yield of the engineered antibody Hm2E8b in the supernatant was 13.3 μg/mL expressed and secreted in the CHO cell system, which reached the secretory quantity of a regular mouse hybridoma cells. Our conclusion is that the IgM type of CD19 mouse antibody can be successfully engineered into an IgG1 type human-mouse chimeric antibody with similar affinity and biological activity. The yield of the Hm2E8b expression and secretion in CHO cell system was adequate to facilitate further development for therapeutic purpose.