Structural requirements of the major protective antibody to Haemophilus influenzae type b

Germline-encoded neutralization of a Staphylococcus aureus virulence factor by the human antibody repertoire

Staphylococcus aureus is both an important pathogen and a human commensal. To explore this ambivalent relationship between host and microbe, we analysed the memory humoral response against IsdB, a protein involved in iron acquisition, in four healthy donors. Here we show that in all donors a heavily biased use of two immunoglobulin heavy chain germlines generated high affinity (pM) antibodies that neutralize the two IsdB NEAT domains, IGHV4-39 for NEAT1 and IGHV1-69 for NEAT2. In contrast to the typical antibody/antigen interactions, the binding is primarily driven by the germline-encoded hydrophobic CDRH-2 motifs of IGHV1-69 and IGHV4-39, with a binding mechanism nearly identical for each antibody derived from different donors. Our results suggest that IGHV1-69 and IGHV4-39, while part of the adaptive immune system, may have evolved under selection pressure to encode a binding motif innately capable of recognizing and neutralizing a structurally conserved protein domain involved in pathogen iron acquisition.

Structures of Preferred Human IgV Genes-Based Protective Antibodies Identify How Conserved Residues Contact Diverse Antigens and Assign Source of Specificity to CDR3 Loop Variation

The human Ab response to certain pathogens is oligoclonal, with preferred IgV genes being used more frequently than others. A pair of such preferred genes, IGVK3-11 and IGVH3-30, contributes to the generation of protective Abs directed against the 23F serotype of the pneumonococcal capsular polysaccharide of Streptococcus pneumoniae and against the AD-2S1 peptide of the gB membrane protein of human CMV. Structural analyses of Fab fragments of mAbs 023.102 and pn132p2C05 in complex with portions of the 23F polysaccharide revealed five germline-encoded residues in contact with the key component, l-rhamnose. In the case of the AD-2S1 peptide, the KE5 Fab fragment complex identified nine germline-encoded contact residues. Two of these germline-encoded residues, Arg91L and Trp94L, contact both the l-rhamnose and the AD-2S1 peptide. Comparison of the respective paratopes that bind to carbohydrate and protein reveals that stochastic diversity in both CDR3 loops alone almost exclusively accounts for their divergent specificity. Combined evolutionary pressure by human CMV and the 23F serotype of S. pneumoniae acted on the IGVK3-11 and IGVH3-30 genes as demonstrated by the multiple germline-encoded amino acids that contact both l-rhamnose and AD-2S1 peptide.

Restricted V gene usage and VH/VL pairing of mouse humoral response against the N-terminal immunodominant epitope of the amyloid β peptide

Over the last decade, the potential of antibodies as therapeutic strategies to treat Alzheimer's disease (AD) has been growing, based on successful experimental and clinical trials in transgenic mice. Despite, undesirable side effects in humans using an active immunization approach, immunotherapy still remains one of the most promising treatments for AD. In this study, we analyzed the V genes of twelve independently isolated monoclonal antibodies raised against the N-terminal immunodominant epitope of the amyloid β peptide (Aβ or A beta). Surprisingly, we found a high and unusual level of restriction in the VH/VL pairing of these antibodies. Moreover, these antibodies mostly differ in their heavy chain complementary determining region 3 (HCDR3) and the residues in the antibodies which contact Aβ are already present in the germline V-genes. Based on these observations and or co-crystal structures of antibodies with Aβ, the aim of the current study was to better understand the role of antibody V-domains, HCDR3 regions, key contact residue (H58) and germline encoded residues in Aβ recognition. For that purpose, we designed and produced a range of recombinant Fab constructs. All the Fabs were tested and compared by surface plasmon resonance on Aβ(1-16), Aβ(1-42) high molecular weight and Aβ(1-42) low molecular weight soluble oligomers. Although all the Fabs recognized the Aβ(1-16) peptide and the Aβ(1-42) high molecular weight soluble oligomers, they did not bind the Aβ(1-42) low molecular weight soluble oligomers. Furthermore, we demonstrated that: (1) an aromatic residue at position H58 in the antibody is essential in the recognition of Aβ and (2) Fabs based on germline V-genes bind to Aβ monomers with a low affinity. These findings may have important implications in designing more effective therapeutic antibodies against Aβ.

Human recombinant antibodies against Plasmodium falciparum merozoite surface protein 3 cloned from peripheral blood leukocytes of individuals with immunity to malaria demonstrate antiparasitic properties

Immunoglobulins from individuals with immunity to malaria have a strong antiparasitic effect when transferred to Plasmodium falciparum malaria infected patients. One prominent target of antiparasitic antibodies is the merozoite surface antigen 3 (MSP-3). We have investigated the antibody response against MSP-3 residues 194 to 257 (MSP-3(194-257)) on the molecular level. mRNA from peripheral blood leukocytes from clinically immune individuals was used as a source of Fab (fragment antibody) genes. A Fab-phage display library was made, and three distinct antibodies designated RAM1, RAM2, and RAM3 were isolated by panning. Immunoglobulin G1 (IgG1) and IgG3 full-length antibodies have been produced in CHO cells. Reactivity with the native parasite protein was demonstrated by immunofluorescence microscopy, flow cytometry, and immunoblotting. Furthermore, the antiparasitic effect of RAM1 has been tested in vitro in an antibody-dependent cellular inhibition (ADCI) assay. Both the IgG1 and the IgG3 versions of the antibody show an inhibitory effect on parasite growth.

Expression of idiotypic antibodies-1 and -2 and breastfeeding in relation to antibody levels against Haemophilus influenzae type B in children

The aim of the study was to determine the concentrations of serum antibodies against Haemophilus influenzae type b in preschool children in relation to the distribution of idiotypic antibodies 1 and 2 (Id-1 and Id-2) and the exposure to breastfeeding in infancy. Sera were obtained from 74 control children recruited in an earlier case-control study before the introduction of general Hib vaccination. Duration of breastfeeding was monitored, and prevalence of noninvasive infections was registered. Concentrations of IgG1 and IgG2 anti-Hib, as well as of total Id-1 and Id-2, were determined in ELISA. The expression of Id-1 antibodies increased with age in contrast to the Id-2 antibodies that were found only in children up to 24 months of age. Expression of Id-1 antibodies was positively correlated with higher anti-Hib levels of both the IgG1 and IgG2 isotype. Children expressing Id-2 antibodies showed higher IgG2 anti-Hib concentrations than those who did not have Id-2 (P = 0.001). The concentrations of neither Id-1 nor Id-2 antibodies were related to the duration of breastfeeding. Duration of breastfeeding was related to increased anti-Hib IgG2 in healthy children above 18 months of age. These study shows that the expression of idiotype-1 and idiotype-2 antibodies was associated with higher IgG2 anti-Hib concentration and that breastfeeding could enhance the anti-Hib IgG2 production in children.

Correlation of molecular characteristics, isotype, and in vitro functional activity of human antipneumococcal monoclonal antibodies

Structure-function correlations of pneumococcal antibodies are important in predicting how changes in the pneumococcus (Pnc)-specific B-cell repertoire will influence humoral immunity against invasive Pnc disease. Using a unique panel of human hybridomas derived from memory B cells after pneumococcal conjugate vaccination, we analyzed the structure-function relationship of nine monoclonal antibodies (MAbs) reactive to Pnc polysaccharides. The avidities of the antibodies correlated with the avidity of donor immune serum (R, 0.7; P < 0.025), and this relationship was particularly strong for immunoglobulin A clones (R, 1; P < 0.0005), suggesting that the MAbs may represent important clones contributing to serological memory. Common heavy-light chain combinations and amino acid replacement mutations were seen for clones with the same serospecificity from different individuals. The two highest-avidity MAbs used Vh3-48, and two MAbs with the same serospecificity, using the same V gene pairings (Vh3-7 and Vk2A17), had similar avidities, suggesting that canonical V gene use makes an important contribution to avidity. Although all clones had mutation levels consistent with their being derived from memory B cells, low levels of replacement mutation were associated with high avidities. This relationship was strongest for Vh genes (R, 0.8; P < 0.01). Opsonophagocytosis was demonstrated for all clones, and there was a trend toward clones using canonical genes with low levels of mutation having high opsonophagocytic activities (R, 0.5). These data suggest that the use of canonical genes in the Pnc antibody response is associated with highly functional antibodies and that most somatic mutations seen in these genes are not antigen selected.

Structure of a non-camelized human M12-VH domain at 1.5Å resolution

A non-camelized human V(H) domain has been crystallized through limited in vitro proteolysis of scFvM12 antibody fragment. The protease addition results in the complete degradation of the M12-V(L) domain, linker, and purification tags. The structure solved up to 1.5A resolution having good stereochemistry with a R(cryst) factor of 15.8% and R(free) factor of 19.7%. Dihedral angle values comparison of the first and the second complementarity-determining region (CDR) of M12-V(H) domain with an average values show a significant deviation; therefore, M12-V(H) domain structure indicates either the existence of a new canonical subclass or a link among the subclasses of canonical main-chain conformation in V(H)3 family. The presence of uncommon hydrogen bond between Ser-H50 and Tyr-H97 has pulling effect on CDR-H3 loop. The interface area buried by CDR-H3 loop indicates the partial coverage of the hydrophobic V(L)-V(H) interface. The isolated M12-V(H) domain was found soluble up to 0.35 mM. This result would be helpful in structure based designing of an isolated human single domain antibody fragments for biotechnological and pharmaceutical applications such as cancer.

Antibody repertoires in infants and adults: effects of T-independent and T-dependent immunizations

Polysaccharide(PS)-encapsulated bacteria such as Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis are among the most prevalent bacterial pathogens of humans. Infections caused by these organisms are both common (otitis media, sinusitis) and severe (meningitis, bacteremia). Antibodies directed against the capsular PS of encapsulated bacteria prevent infection by promoting opsonophagocytic killing. Most bacterial PS, however, are type II T-cell-independent (TI-2) antigens that are poorly immunogenic in young children at highest risk of developing disease. Conjugation of bacterial PS to a protein carrier converts the immune response to a T-cell-dependent (TD) form and significantly improves the immunogenicity of PS, especially in infants. H. influenzae type b (Hib) is a major cause of invasive infection in non-immune children. The medical importance of this pathogen and the availability of both TI-2 and TD Hib PS vaccine formulations have made the human anti-Hib-PS immune response an excellent model for the study of the biology of these B cell responses.

Structural determinants of the human idiotype HibId-1

The human antibody response to the capsular polysaccharide of Haemophilus influenzae type b is predominated by antibodies expressing a light-chain-associated idiotype designated HibId-1. HibId-1 is expressed by kappa light chains encoded by either the A2 or A18 variable region genes. In this report we use site-directed mutagenesis and molecular modeling to show that HibId-1 expression is determined by residues in the first and second complimentarity determining regions that are widely separated in the primary sequence, but closely juxtaposed by the tertiary folding of the mature light chain molecule. Of the known human light chains, only alleles of A2 and A18 encode these residues at these positions in their germline configuration. VIG10, a mouse monoclonal antibody of unknown specificity that expresses HibId-1, and 23F.2, an A2-utilizing Streptococcus pneumoniae 23F polysaccharide-specific human Fab fragment that lacks HibId-1, provide examples of the HibId-1 determinant both arising and being lost by somatic mutation. In addition, we show that the residues responsible for HibId-1 expression can be disassociated from those required for antigen binding.

Prediction of the interacting surfaces in a trimolecular complex formed between the major dust mite allergen Der p 1, a mouse monoclonal anti-Der p 1 antibody, and its anti-idiotype

BACKGROUND

Two mouse monoclonal antibodies (mAbs) have been described recently; namely, mAb 2C7 (IgG2b kappa), which is directed against the major house dust mite allergen Der p 1, and mAb 2G10 (IgG1 kappa), which is an anti-idiotypic antibody raised against mAb 2C7. The anti-idiotype mAb 2G10 does not block the binding of mAb 2C7 to Der p 1, which means that mAb 2C7 can simultaneously bind to Der p 1 and to mAb 2G10, thereby generating a trimolecular complex consisting of antigen-idiotype-anti-idiotype.

AIMS

To sequence and model the V region of the anti-idiotypic antibody mAb 2G10 to enable the prediction of the interacting surfaces in the trimolecular complex consisting of Der p 1-mAb 2C7-mAb 2G10.

METHODS

DNA sequencing of mAb 2G10 was carried out and the Swiss Model and Swiss PDB-Viewer programs were used to build a three dimensional model of the trimolecular complex.

RESULTS

Complementarity of shape and charge was revealed when comparing the protrusion of the previously determined Der p 1 epitope (Leu147-Gln160) with the cavity formed by the complementarity determining regions (CDRs) of mAb 2C7. Such complementarity was also observed between the mAb 2C7 epitope predicted to be recognised by mAb 2G10 (residues Lys19 from framework region 1 (FRW1) and Ser74-Gln81 from FRW3) and residues from the CDRs of mAb 2G10 (a negatively charged patch flanked by the residues Asp55H/Glu58H and Glu27L/Glu27cL). As expected, the location of the mAb 2C7 epitope recognised by mAb 2G10 does not appear to interfere with the binding of Der p 1 to mAb 2C7.

CONCLUSION

Although the results obtained represent only an approximation, they nevertheless provide a rare insight into how an antigen (Der p 1) might bind to its antibody (mAb 2C7) while in complex with an anti-idiotype (mAb 2G10).

Analysis of 'natural' and vaccine-induced haemophilus influenzae type B capsular polysaccharide serum antibodies for 3H1, a V3-23-associated idiotope

The variable (V-) region repertoire of antibodies (Abs) to Haemophilus influenzae capsular polysaccharide (Hib PS) has been extensively studied in individuals vaccinated against the microbe, but to a lesser extent in subjects who generated such Abs in response to a 'natural' encounter with this microbe or its antigenic mimics. To gain an insight into the repertoire of Hib PS-reactive Abs in vaccinated and non-vaccinated individuals, we used a monoclonal Ab, 3H1, which detects an idiotypic marker associated with an Ab V-region gene, V3-23. We show here that Hib PS-reactive Abs with detectable 3H1 idiotope can be quantified by an indirect inimunoezymatic assay in serum samples of non-vaccinated healthy adults as well as of recently vaccinated healthy infants. The percentage of Abs that was simultaneously Hib PS-reactive and 3H1-positive ranged widely (from 0 to 68%) among individual serum samples from both groups of subjects. No dramatic differences in the expression of 3H1 idiotope on Hib PS-reactive Abs were found between vaccinated and non-vaccinated individuals. Our results are consistent with the hypothesis that the utilization of V-region genes in Hib PS-reactive Abs that individuals generate after a 'natural' encounter with Hib PS or its mimics is similar to that in these Abs elicited by Hib PS conjugate vaccines.