The human antibody V region repertoire to the type B capsular polysaccharide of Haemophilus influenzae

A Structural Model for the Ligand Binding of Pneumococcal Serotype 3 Capsular Polysaccharide-Specific Protective Antibodies

Capsular polysaccharides (CPSs) are major virulence factors that decorate the surfaces of many human bacterial pathogens. In their pure form or as glycoconjugate vaccines, CPSs are extensively used in vaccines deployed in clinical practice worldwide. However, our understanding of the structural requirements for interactions between CPSs and antibodies is limited. A longstanding model based on comprehensive observations of antibody repertoires binding to CPSs is that antibodies expressing heavy chain variable gene family 3 (VH3) predominate in these binding interactions in humans and VH3 homologs in mice. Toward understanding this highly conserved interaction, we generated a panel of mouse monoclonal antibodies (MAb) against Streptococcus pneumoniae serotype 3 CPS, determined an X-ray crystal structure of a protective MAb in complex with a hexasaccharide derived from enzymatic hydrolysis of the polysaccharide, and elucidated the structural requirements for this binding interaction. The crystal structure revealed a binding pocket containing aromatic side chains, suggesting the importance of hydrophobicity in the interaction. Through mutational analysis, we determined the amino acids that are critical in carbohydrate binding. Through elucidating the structural and functional properties of a panel of murine MAbs, we offer an explanation for the predominant use of the human VH3 gene family in antibodies against CPSs with implications in knowledge-based vaccine design.

Haemophilus parasuis infection activates NOD1/2-RIP2 signaling pathway in PK-15 cells

Haemophilus parasuis, an important swine pathogen, was recently proven able to invade into endothelial or epithelial cell in vitro. NOD1/2 are specialized NLRs that participate in the recognition of pathogens able to invade intracellularly and therefore, we assessed that the contribution of NOD1/2 to inflammation responses during H. parasuis infection. We observed that H. parasuis infection enhanced NOD2 expression and RIP2 phosphorylation in porcine kidney 15 cells. Our results also showed that knock down of NOD1/2 or RIP2 expression respectively significantly decreased H. parasuis-induced NF-κB activity, while the phosphorylation level of p38, JNK or ERK was not changed. Moreover, real-time PCR result showed that NOD1, NOD2 or RIP2 was involved in the expression of CCL4, CCL5 and IL-8. Inhibition of NOD1 and NOD2 significantly reduced CCL5 promoter activity, even in a more effective way compared with inhibition of TLR.

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.

Mouse marginal zone B cells harbor specificities similar to human broadly neutralizing HIV antibodies

A series of potent, broadly neutralizing HIV antibodies have been isolated from B cells of HIV-infected individuals. VRC01 represents a subset of these antibodies that mediate neutralization with a restricted set of IGHV genes. The memory B cells expressing these antibodies were isolated years after infection; thus, the B-cell subpopulation from which they originated and the extent of participation in the initial HIV antibody response, if any, are unclear. Here we evaluated the frequency of anti-gp120 B cells in follicular (FO) and marginal zone (MZ) B-cell compartments of naïve WT mice and comparable human populations in uninfected individuals. We found that in non-HIV-exposed humans and mice, the majority of gp120-reactive B cells are of naïve and FO phenotype, respectively. Murine FO B cells express a diverse antibody repertoire to recognize gp120. In contrast, mouse MZ B cells recognize gp120 less frequently but preferentially use IGHV1-53 to encode gp120-specific antibodies. Notably, IGHV1-53 shows high identity to human IGHV1-2*02, which has been repeatedly found to encode broadly neutralizing mutated HIV antibodies, such as VRC01. Finally, we show that human MZ-like B cells express IGHV1-2*02, and that IGHV1-53 expression is enriched in mouse MZ B cells. These data suggest that efforts toward developing an HIV vaccine might consider eliciting protective HIV antibody responses selectively from alternative B-cell populations harboring IGHV gene segments capable of producing protective antibodies.

Somatic hypermutation and diverse immunoglobulin gene usage in the human antibody response to the capsular polysaccharide of Streptococcus pneumoniae Type 6B

Combinatorial cloning and expression library analysis were used to determine the expressed human antibody repertoire specific for the capsular polysaccharide (PS) of Streptococcus pneumoniae serotype 6B. Sequence analysis of 55 6B-specific antibody Fab fragments isolated from six vaccinated donors reveal that different individuals used a variety of heavy and light chain germ line variable (V) region genes to form pneumococcal capsular PS (PPS) 6B-specific paratopes. Within each donor, however, the response was more restricted, with five of the six donors using at most one or two gene pairs to form combining sites. Analysis also indicated that although the response in each donor was oligoclonal in terms of variable gene usage, the combination of extensive somatic hypermutation, deletion of germ line-encoded residues, insertion of non-germ line-encoded residues, and intraclonal isotype switching generated a surprising degree of paratope diversity within the individuals analyzed. In contrast to previously studied PS-specific responses, we find that the PPS 6B repertoire makes use of a diverse collection of heavy-chain and light-chain V region gene products to form specific paratopes, with no apparent tendency for conservation of immunoglobulin gene usage between individuals.

Remarkably similar antigen receptors among a subset of patients with chronic lymphocytic leukemia

Studies of B cell antigen receptors (BCRs) expressed by leukemic lymphocytes from patients with B cell chronic lymphocytic leukemia (B-CLL) suggest that B lymphocytes with some level of BCR structural restriction become transformed. While analyzing rearranged V(H)DJ(H) and V(L)J(L) genes of 25 non-IgM-producing B-CLL cases, we found five IgG(+) cases that display strikingly similar BCRs (use of the same H- and L-chain V gene segments with unique, shared heavy chain third complementarity-determining region [HCDR3] and light chain third complementarity-determining region [LCDR3] motifs). These H- and L-chain characteristics were not identified in other B-CLL cases or in normal B lymphocytes whose sequences are available in the public databases. Three-dimensional modeling studies suggest that these BCRs could bind the same antigenic epitope. The structural features of the B-CLL BCRs resemble those of mAb's reactive with carbohydrate determinants of bacterial capsules or viral coats and with certain autoantigens. These findings suggest that the B lymphocytes that gave rise to these IgG(+) B-CLL cells were selected for this unique BCR structure. This selection could have occurred because the precursors of the B-CLL cells were chosen for their antigen-binding capabilities by antigen(s) of restricted nature and structure, or because the precursors derived from a B cell subpopulation with limited BCR heterogeneity, or both.

Recurrent variable region gene usage and somatic mutation in the human antibody response to the capsular polysaccharide of Streptococcus pneumoniae type 23F

Combinatorial cloning and expression library analysis were used to isolate human antibody Fab fragments specific for the capsular polysaccharide of Streptococcus pneumoniae serotype 23F. Thirty 23F-specific Fabs were isolated from seven vaccinated donors, and the sequences of the heavy (H)- and light (L)-chain variable regions were determined. All individuals utilized either the Vkappa A23 L chain, the Vkappa L6 L chain, or both chains in forming the 23F-specific combining site. Vkappa A23 L chains paired primarily with VH3-23 H chains. Vkappa L6 L chains were more promiscuous in heavy-chain usage between individuals. Both H and L chains were mutated, primarily in the complementarity-determining regions, compared to their closest germ line counterpart, suggesting a recall response that has undergone affinity maturation. H-chain isotypes were reflective of those found in the serum. Shared somatic modifications demonstrated that immunoglobulin G2 (IgG2) and IgA antibodies arose from the same somatically matured B cell. Our results indicate that the response to the serotype 23F pneumococcal capsular polysaccharide is oligoclonal within the individual, with one or two paratope families accounting for the majority of expressed antibody. We also determined that, in spite of the combinatorial diversity available to the immune system, the 23F-specific response is highly restricted at the population level, with the same two L-chain-determined paratope families recurring in all individuals. Lastly, analysis of the isolated Fabs indicate all have undergone extensive somatic mutation, as well as class switch, maturational events that presumably require the participation of T cells.

The immunoglobulin kappa gene families of human and mouse: a cottage industry approach

Some aspects of the work of our group on the human and mouse immunoglobulin kappa genes are reviewed. The human kappa locus contains a large duplication: a 600 kb Ckappa-proximal copy with 40 Vkappa genes is found in the close vicinity of a 440 kb Ckappa-distal copy with 36 very similar, but not identical, Vkappa genes. The chimpanzee has only the Ckappa-proximal copy of the locus. The kappa locus of the mouse is close to 3.2 Mb in size, of which 3.1 Mb have been cloned in four contigs, leaving three small gaps of together about 90 kb; 140 Vkappa genes and pseudogenes were localized and sequenced. In parallel to the elucidation of the structure of the kappa loci, the mechanisms of the V-J rearrangement, somatic hypermutation and kappa gene expression were studied. Various polymorphisms were detected in the human population and a number of haplotypes defined. In addition to the Vkappa genes within the loci numerous Vkappa orphons were localized on different chromosomes. Comparing the kappa loci of different species allows some interesting conclusions as to the evolution of this multigene family. Finally our strategy of elucidating the structure and function of the kappa loci, which has been termed a 'cottage industry approach', is discussed in relation to the large-scale genome analysis as pursued today using automated methods.

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

Protective antibodies to the important childhood pathogen Haemophilus influenzae type b (Hib) are directed against the capsular polysaccharide (HibCP). Most of the antibody is encoded by a well-defined set of ("canonical") immunoglobulin genes, including the Vkappa A2 gene, and expresses an idiotypic marker (HibId-1). In comparison to noncanonical antibodies, the canonical antibody is generally of higher avidity, shows higher levels of in vitro bactericidal activity, and is more protective in infant rats. Using site-directed mutagenesis, we here characterize canonical HibCP antibodies expressed as antigen-binding fragments (Fabs) in Escherichia coli, define amino acids involved in antigen binding and idiotype expression, and propose a three-dimensional structure for the variable domains. We found that canonical Fabs, unlike a noncanonical Fab, bound effectively to HibCP in the absence of somatic mutations. Nevertheless, pronounced mutation-based affinity maturation was demonstrated in vivo. An almost perfect correlation was found between unmutated gene segments that mediated binding in vitro and those encoding canonical HibCP antibodies in vivo. Thus, the Vkappa A2a gene could be replaced by the A2c gene but not by the highly homologous sister gene, A18b, corresponding to the demonstrated usage of A2c but not of A18b in vivo. Similarly, only Jkappa1 and Jkappa3, which predominate in the response in vivo, were able to facilitate binding in vitro. These findings suggest that the restricted immunoglobulin gene usage in HibCP antibodies reflects strict structural demands ensuring relatively high affinity prior to somatic mutations-requirements met by only a limited spectrum of immunoglobulin gene combinations.

Decreased Frequency of Rearrangement due to the Synergistic Effect of Nucleotide Changes in the Heptamer and Nonamer of the Recombination Signal Sequence of the Vκ Gene A2b, Which Is Associated with Increased Susceptibility of Navajos to Haemophilus influenzae Type b Disease

Navajos and genetically related populations have a 10-fold increased incidence of Haemophilus influenzae type b (Hib) disease compared with control populations. The Vκ gene A2 is used to encode the majority of anti-Hib Abs, and these are the highest affinity anti-Hib Abs. Navajos carry a different allele of the A2 gene segment (A2b) that is defective in its ability to undergo V-J recombination. The A2b allele has only three nucleotide changes from the commonly occurring A2a allele, two of which could potentially affect its ability to recombine. In this study we used two independent in vitro assays to test whether the nucleotide change found in the A2b promoter and/or in the A2b recombination signal sequence (RSS) might be responsible for the decrease in recombination frequency observed in vivo. Using a luciferase reporter gene assay, we found no significant difference between A2a and A2b promoter activities. However, the competition recombination substrate assay showed a 4.5-fold reduction in the relative frequency of recombination of the A2b RSS compared with A2a. We show that this decreased frequency is due to a synergistic effect of the unique nucleotide change present in the heptamer of the A2b RSS and the shared nucleotide change present in the nonamer of both A2b and A2a. This in vitro relative frequency of rearrangement is not significantly different from that observed in vivo; therefore, the A2b RSS is probably the factor associated with the increased susceptibility to Hib disease among individuals carrying the A2b allele.

Heterogeneity of antibodies reactive with the dominant antigen of Actinobacillus actinomycetemcomitans

The serotype b-specific carbohydrate antigen (SbAg) of Actinobacillus actinomycetemcomitans Y4 is reported to be the O antigen of lipopolysaccharide, and the highest titers of serum antibody reactive with A. actinomycetemcomitans in early-onset periodontitis (EOP) patients bind SbAg. These high titers of serum antibody reactive with SbAg are associated with a lesser extent and severity of periodontal disease. The aim of this study was to determine if a limited number of genes code for anti-SbAg antibodies as has been shown for immunoglobulin G (IgG) reactive with the type b polysaccharide from Haemophilus influenzae. Serum IgG reactive with the SbAg was prepared from 20 high-titer EOP patients by affinity chromatography. The IgG subclass concentrations were determined, and heterogeneity was analyzed by isoelectric focusing (IEF). IgG2 was the dominant subclass (83% of total IgG) in the anti-SbAg IgG fraction and represented an average of 1.33% of total serum IgG2. The IgG2 reactive with SbAg was isolated from the affinity-purified IgG fraction by affinity chromatography with protein A and subclass-specific monoclonal antibodies. On IEF gels, only 4 to 20 bands were observed in the anti-SbAg IgG fractions, indicating limited heterogeneity. N-terminal amino acid sequence analysis of eight representative anti-SbAg IgG2 preparations indicated that variable heavy and light chains consisted largely of V(H)III and V(kappa)II, respectively. However, a significant fraction of anti-SbAg may use V(H) and V(lambda) genes with blocked N termini. In short, these findings indicate that IgG reactive with SbAg is very much like the antibody reactive with H. influenzae type b polysaccharide. Similarities include IgG2 dominance, limited bands on IEF gels, supporting an oligoclonal response, and use of genes from V(H)III and V(kappa)II regions.

Association of placental transfer of anti-Haemophilus influenzae type b polysaccharide antibodies with their V regions

Immunization of mothers during pregnancy may be an effective means of providing protection to infants during the first months of life against many pathogens. Previous studies have identified factors that influence the transfer of immunoglobulin across the placenta, including the time of vaccination during pregnancy and isotypes of specific immunoglobulins. By studying antibodies to Haemophilus influenzae type b polysaccharide (Hib-PS) in 26 pairs of maternal-cord sera obtained from unimmunized healthy women and 22 pairs of maternal-cord sera from women immunized with one of three different Hib vaccines, we have found that the immunoglobulin transfer is also dependent on the V region of antibodies. Anti-Hib-PS derived from the V kappa II gene "A2" was transferred about ten times more efficiently to the fetus than other anti-Hib-PS antibodies (20% vs 1-2%). It was found that antibodies derived from the A2 V kappa gene are primarily IgG whereas other antibodies are preferentially associated with the IgM isotype. The potential association between the antibody V region with preferential placental transfer should be considered for future studies involving maternal immunization.

The V-region repertoire of Haemophilus influenzae type b polysaccharide antibodies induced by immunization of infants

Haemophilus influenzae type b (Hib) is a significant pathogen for young children, and three Hib vaccines (named PRP-OMPC, HbOC, and PRP-T) are currently available for young children. Extensive studies of anti-Hib polysaccharide (PS) antibodies (Abs) have shown that the V regions of Abs against the Hib PS comprise a VH gene in the VH3 gene family and a VL gene from various K kappa and V lambda subgroups. To study immunogenic properties of the three vaccines in young children, we determined the VL subgroups and avidities of anti-Hib-PS Abs induced by the three clinically available conjugate vaccines. Ab avidity was measured by determining the concentration of a Hib-PS oligomer that abrogates half of the binding of immunoglobulin G anti-Hib-PS Abs to microwells. The PRP-OMPC vaccine induced lower-avidity Abs than the prelicensure HbOC vaccine (P = 0.05). When we compared anti-Hib-PS Abs expressing V kappa Ia, V kappa II, and V lambda subgroups, a greater Ab response was induced by the prelicensure HbOC vaccine than other vaccines (P < 0.05). When anti-Hib-PS Abs with the V kappa III subgroup were compared, however, both PRP-T and prelicensure HbOC vaccines induced a comparable response, which in turn was greater than those induced by the PRP-OMPC or the postlicensure HbOC vaccine (P < 0.001). The VL repertoire of Abs induced with the prelicensure HbOC or PRP-T vaccine in young children is dominated (about 80%) by anti-Hib-PS Abs using subgroup V kappa II. However, anti-Hib-PS using V kappa II VL accounts for only about 40% of the total anti-Hib-PS Abs induced with the PRP-OMPC vaccine or the postlicensure HbOC. Our data suggest that immunogenic properties of Hib vaccines in young children vary depending on the vaccine preparations as well as the vaccine types.

The human antibody repertoire: heavy and light chain variable region gene usage in six alloantibodies specific for human HLA class I and class II alloantigens

Peripheral blood B lymphocytes have been isolated from healthy individuals who were immunized with lymphocytes from HLA-incompatible donors and transformed with Epstein-Barr virus to produce human monoclonal cell lines specific for human HLA molecules. The cell lines have been previously characterized and are known to bind to various class I and class II alloantigens. In this report we describe the molecular characterization of the heavy and light chain variable region gene segments that are utilized by these monoclonal antibodies. Using the polymerase chain reaction and primer pairs specific for the respective constant region and VH or VL family, rearranged variable region gene segments were amplified from cDNA from individual cell lines. Products were then subcloned, sequenced and analysed for gene usage and apparent somatic mutation. The results show that the VH3 gene family predominates in a group of six heavy chains (four out of six) with one VH1 and one VH4 gene segment. The light chain variable region gene family usage is more diverse with 2 V kappa 3, 1 V kappa 1, 2 V lambda 2 and 1 V lambda 3. The extent of apparent somatic mutation is minimal, relative to our previous observations in a group of high affinity human monoclonal antibodies specific for pathogenic organisms.

Functional capacities of clonal antibodies to Haemophilus influenzae type b polysaccharide

Haemophilus influenzae type b (Hib) is an important pathogen for young children, and children can be protected with antibodies (Abs) to Hib polysaccharide (PS) capsule, a linear polymer of ribosyl ribitol phosphate. The structure of anti-Hib-PS Abs has been well characterized at the molecular level; about two-thirds of anti-Hib-PS Abs use a V kappa gene named A2, and the remaining anti-Hib-PS Abs use one of many other VL genes. In order to understand the structural basis for the variability in the function of these Abs, we prepared 18 clonally pure Abs from adults and studied their affinity, avidity, bactericidal potency in vitro, and ability to reduce bacteremia in newborn rats. Affinities and avidities were determined as the inverse of the concentrations of short (3 repeating units) and long (20 repeating units) ligands which could bind 50% of anti-Hib-PS Ab in solution, respectively. No significant correlations between the protection of newborn rats and affinity (r = 0.02) or avidity (r = 0.16) were observed. The amount of Ab required to kill 50% of bacteria in vitro decreased with avidity (r = -0.32), as expected. However, Abs with high affinity were unexpectedly found to have less bactericidal activity (r = 0.38). This suggests that avidity may be a better predictor of Ab function than affinity. Affinity and avidity results were negatively correlated (r = 0.76, P = 0.0022), and Abs that had A2 V kappa gene products had higher avidity (P < 0.05) and lower affinity (P = 0.06) than Abs that had other VL genes. A possible explanation of these observations is that the epitope for Abs with the A2 gene is within the Hib-PS chain itself, whereas the epitope for Abs with a non-A2 gene is the terminus of Hib-PS.

Predominant V-region gene configurations in the human antibody response to Haemophilus influenzae capsule polysaccharide

The antibody response to Haemophilus influenzae type b polysaccharide (Hib PS) is known to be encoded by a few V-region genes. We have obtained four human monoclonal Hib PS antibodies from four healthy adult subjects immunized with diphtheria toxin-conjugated Hib PS vaccine. The VH gene segments that encode for these antibodies belong to the VH3 gene family, of which two are related to the V3-23 gene and two to the VH3b subfamily. Both hybridomas that express a V3-23-related gene use short D-segments (3 bp), the JH6 gene segment and a V kappa gene derived from the A2 germline gene. The two hybridomas that express VH3b genes use D-segments of conventional length (24-33 bp), the JH4 gene segment and a non-A2 V kappa gene. Comparison of our sequences with those reported by others suggests that the above patterns of V-region gene segment association exemplify two V-region gene configurations that are predominant in the Hib PS antibody response. The first configuration is reminiscent of antibodies produced by B-1 B cells while the second is more characteristic of antibodies produced by conventional B cells. The possibility that these two configurations, in fact, represent the products of two different B cell lineages remains to be elucidated.

The immunoglobulin kappa locus-or-what has been learned from looking closely at one-tenth of a percent of the human genome

The immunoglobulin kappa locus and its immediate surroundings, which are described in the present report, comprise 3 Mb of DNA, i.e., 0.1% or one per mill of the 3000 Mb of the human genome. Based on the work of our group during the past 12 years, we can now (1) depict in much detail the structure of the kappa locus with its 76 V kappa genes and pseudo genes, five J kappa elements and one C kappa gene; (2) specify the size of the germ-line repertoire of kappa light chains, which is one of the sources of the practically unlimited antibody diversity; (3) assign the known transcription products (studied as cDNAs) and kappa proteins to certain germ-line V kappa genes and attribute the differences in sequences to hypermutation and, to a lesser extent, to allelic variation; (4) analyze the hypermutation patterns which may contribute to the understanding of this enigmatic process; (5) describe the V kappa-J kappa rearrangements for half of the V kappa genes by a deletion mechanism and for the other half by a mechanism involving inversions of Mb-sized (i.e., 0.5 mm long) DNA fragments; (6) define various regulatory and other conserved sequence elements; (7) get clues as to the variation of the structure of the kappa locus in different individuals and populations, including a haplotype with only half the number of V kappa genes; (8) interpret many aspects of the evolution of the kappa locus in terms of duplications, insertions, deletions and gene conversions; (9) attribute the formation of the 24 V kappa orphons (i.e., genes outside the locus), whose sequences were determined, to pericentric inversions and other transposition processes; (10) answer a series of questions of biomedical interest; and (11) contribute 12.5 Mb of restriction maps, 1.8 Mb of clones and 250 kb of sequences to the elucidation of the human genome.

Comparison of naturally acquired and vaccine-induced antibodies to Haemophilus influenzae type b capsular polysaccharide

The objective of this study was to assess qualitative differences in the types of Haemophilus influenzae type B (Hib) capsular polysaccharide (polyribosylribitol phosphate [PRP]) antibodies induced in children 15 to 27 months of age by (i) natural exposure, (ii) PRP vaccine, and by (iii) PRP-diphtheria toxoid conjugate vaccine, (iv) PRP-group B Neisseria meningitidis outer membrane vesicle conjugate vaccine, and (v) Haemophilus type B oligosaccharide conjugate vaccine (HbOC). The highest levels of total Hib-PRP antibody measured by radioimmunoassay and immunoglobulin G (IgG) measured by enzyme-linked immunosorbent assay were seen after HbOC immunization. IgG1 Hib-PRP antibodies predominated in all groups, and there were no differences between the groups in the proportion of IgG and IgA Hib-PRP antibodies. However, the proportions of IgM differed significantly by group. The highest proportions of IgM occurred in naturally acquired antibody and after PRP vaccine, and the lowest proportion occurred after HbOC vaccine. IgG light-chain V kappa type alpha PRP antibody was present in all groups, and the level correlated with the total IgG Hib-PRP antibody level. Therefore, HbOC induced the highest concentrations of V kappa II type alpha PRP antibody, and the naturally acquired antibody group had the lowest levels. IgG light-chain V kappa III antibody levels were also highest in the HbOC group, but there was no correlation between V kappa III antibody levels and total amount of IgG Hib-PRP antibody. These data demonstrate qualitative differences in the antibody repertoires induced by natural exposure, the Hib-PRP vaccine, and each of the different Hib conjugate vaccines. We doubt that there are major differences in the protection afforded by these different antibody repertoires, because these differences do not appear to correlate with differences in protective efficacy in older children.

Molecular characterization of human antibodies to bacterial antigens: utilization of the less frequently expressed VH2 and VH6 heavy chain variable region gene families

Structural analysis of the human immunoglobulin repertoire holds promise for determining the basis of variable region gene usage in response to a variety of auto and exogenous antigens. Here we report the nucleotide sequences of the heavy and light chain variable regions expressed by three human monoclonal antibodies specific for two clinically relevant bacterial pathogens, Bordetella pertussis and Haemophilus influenzae type b. The cell lines were derived by in vitro stimulation of lymphocytes from spleen or tonsillar tissue, respectively, and bind to different antigens from the two organisms. The single B. pertussis antibody is of the IgM lambda isotype and utilizes the single VH6 gene segment in combination with a V lambda 2 gene and demonstrates limited somatic mutation, yet is highly indicative of an antigen-driven immune response. One H. influenzae antibody is of the IgG2 lambda isotype and expresses a VH3 gene segment with a V lambda 1 gene, while the second cell line produces an IgG3 lambda antibody expressing a combination of VH2/V lambda 3. Both molecules show evidence of somatic mutation. The D gene segments of the heavy chains vary in length and display limited sequence homology with known germline D segments. As demonstrated previously, JH4 predominates (two JH4 and one JH3) and all three utilize the J lambda 3 gene segment. In addition, we have isolated and sequenced a number of germline VH2 gene segments in an attempt to better understand the nature of the VH2 germline repertoire. In addition to contributing to the understanding of the human antibody repertoire, such clinically relevant molecules may prove to be a source of passive immunotherapy for those at risk to developing disease.