Expression of 12 rabbit IgA C alpha genes as chimeric rabbit-mouse IgA antibodies

Identification and characterization of antibodies elicited by human cystatin C fragment

Amyloid formation is associated with a number of neurodegenerative diseases that affect the independence and quality of life of aging populations. One of rather atypical, occurring at a young age amyloidosis is hereditary cystatin C amyloid angiopathy (HCCAA) related to aggregation of L68Q variant of human cystatin C (hCC). Human cystatin C plays a very important role in many aspects of human health; however, its amyloidogenic properties manifested in HCCAA present a real, lethal threat to some populations and any work on factors that can affect possible influencing hCC aggregation is not to overestimate. It was proved that interaction of hCC with monoclonal antibodies suppresses significantly hCC dimerization process. Therefore, immunotherapy seems to be the right approach toward possible HCCAA treatment. In this work, the hCC fragment encompassing residue 60-70 (in 2 variants: linear peptide and multiple antigenic peptide) was used as an immunogen in rabbit immunization. As a result, specific anti-hCC antibodies were found in both rabbit sera. Surprisingly, rabbit antibodies were obtained after immunization with only a short peptide. The obtained antibodies were characterized, and their influence on the aggregation propensity of the hCC molecules was evaluated. The antibodies turned out not to have any significant influence on the cystatin C dimerization process. Nevertheless, we hope that antibodies elicited in rabbits by other hCC fragments could lead to elaboration of effective treatment against HCCAA.

Are anti-HIV IgAs good guys or bad guys?

An estimated 90% of all HIV transmissions occur mucosally. Immunoglobulin A (IgA) molecules are important components of mucosal fluids. In a vaccine efficacy study, in which virosomes displaying HIV gp41 antigens protected most rhesus monkeys (RMs) against simian-human immunodeficiency virus (SHIV), protection correlated with vaginal IgA capable of blocking HIV transcytosis in vitro. Furthermore, vaginal IgG exhibiting virus neutralization and/or antibody-dependent cellular cytotoxicity (ADCC) correlated with prevention of systemic infection. In contrast, plasma IgG had neither neutralizing nor ADCC activity. More recently, a passive mucosal immunization study provided the first direct proof that dimeric IgAs (dIgAs) can prevent SHIV acquisition in RMs challenged mucosally. This study compared dimeric IgA1 (dIgA1), dIgA2, or IgG1 versions of a human neutralizing monoclonal antibody (nmAb) targeting a conserved HIV Env epitope. While the nmAb neutralization profiles were identical in vitro, dIgA1 was significantly more protective in vivo than dIgA2. Protection was linked to a new mechanism: virion capture. Protection also correlated with inhibition of transcytosis of cell-free virus in vitro. While both of these primate model studies demonstrated protective effects of mucosal IgAs, the RV144 clinical trial identified plasma IgA responses to HIV Env as risk factors for increased HIV acquisition. In a secondary analysis of RV144, plasma IgA decreased the in vitro ADCC activity of vaccine-induced, Env-specific IgG with the same epitope specificity. Here we review the current literature regarding the potential of IgA – systemic as well as mucosal – in modulating virus acquisition and address the question whether anti-HIV IgA responses could help or harm the host.

Development of standard operating procedures to obtain longitudinal vaginal specimens from nulliparous rabbits as part of HIV vaccine mucosal immunogenicity studies

The New Zealand white rabbit model (Oryctolagus cuniculus) is widely used to test whether HIV vaccine candidates elicit systemic antibody responses; however, its use in mucosal immunology has not been fully exploited due to the difficulty in collecting mucosal specimens longitudinally and reproducibly. Here we describe feasible and non-feasible methods to collect vaginal and nasal specimens from nulliparous rabbits. Non-feasible methods were those resulting in poor reproducibility and considerable animal twitching during sampling, whereas feasible methods resulted in no animal twitching and potential for sampling reproducibility. Standard operating procedures (SOPs) were implemented to collect vaginal swabs yielding total IgA titres ranging from 12,500 to 312,500. Intranasal immunisation with a naked DNA vaccine encoding HIV gp140 elicited HIV envelope-specific IgA detectable in nasal but not in vaginal secretions. Our methods provide an alternative to reliably assess pre- and post-vaccination mucosal antibody titres longitudinally in rabbits as part of mucosal HIV vaccine immunogenicity studies.

Recombinant IgA Antibodies

The production of monoclonal antibodies and the development of recombinant antibody technology have made antibodies one of the largest classes of drugs in development for prophylactic, therapeutic and diagnostic purposes. Currently, all of the Food and Drug Administration (FDA)- approved antibodies are immunoglobulin Gs (IgGs). However, more than 95%of the infections are initiated at the mucosal surfaces, where IgA is the primary immune effector antibody.

A comparison of the binding of secretory component to immunoglobulin A (IgA) in human colostral S-IgA1 and S-IgA2

A detailed investigation of the binding of secretory component to immunoglobulin A (IgA) in human secretory IgA2 (S-IgA2) was made possible by the development of a new method of purifying S-IgA1, S-IgA2 and free secretory component from human colostrum using thiophilic gel chromatography and chromatography on Jacalin-agarose. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of unreduced pure S-IgA2 revealed that, unlike in S-IgA1, a significant proportion of the secretory component was bound non-covalently in S-IgA2. When S-IgA1 was incubated with a protease purified from Proteus mirabilis the secretory component, but not the alpha-chain, was cleaved. This is in contrast to serum IgA1, in which the alpha-chain was cleaved under the same conditions - direct evidence that secretory component does protect the alpha-chain from proteolytic cleavage in S-IgA. Comparisons between the products of cleavage with P. mirabilis protease of free secretory component and bound secretory component in S-IgA1 and S-IgA2 also indicated that, contrary to the general assumption, the binding of secretory component to IgA is different in S-IgA2 from that in S-IgA1.

B cell and antibody repertoire development in rabbits: the requirement of gut-associated lymphoid tissues

The antibody repertoire of rabbits has interested immunologists for decades, in part because of the ease with which large quantities of high affinity antibodies can be obtained in serum, and in part because of the presence of genetic variants, allotypes, within V(H), C(H) and C(L) regions. Studies of these allotypes led to the initial descriptions of allelic exclusion, and neonatal suppression of serum Ig production (allotype suppression), and were instrumental in demonstrating that V and C regions are encoded by separate genes and are usually expressed in cis. The immune system of rabbit continues to be of interest primarily because of the use of both gene conversion and somatic hypermutation to diversify rearranged heavy and light chain genes and the role that gut-associated lymphoid tissues (GALT) and intestinal flora play in developing the primary (preimmune) antibody repertoire.

Functional analysis of I alpha promoter regions of multiple IgA heavy chain genes

The 13 nonallelic IgA H chain genes of rabbit are differentially expressed in vivo. They can be grouped into those expressed at high levels (Calpha4, Calpha5, Calpha6, Calpha9, Calpha10, Calpha12, and Calpha13), those expressed at low levels (Calpha1, Calpha2, Calpha7, and Calpha11), and those that are not expressed (Calpha3 and Calpha8). We tested whether the differential in vivo expression is due to differential responses of the Ialpha promoters to TGF-beta stimulation. We stimulated the rabbit B cell line 55D1 with TGF-beta and, using single-cell RT-PCR, found that expression of germline (GL) transcripts of alpha3 and alpha8 could not be induced. By luciferase reporter gene assay and EMSA we found that the promoters of the unexpressed isotypes Calpha3 and Calpha8 are defective, thereby explaining the absence of IgA3 and IgA8 in vivo. When comparing the promoter activities of the other isotypes we found that the activities did not reflect the degree of in vivo expression. Instead, the promoters of the isotypes expressed at high or low levels promoted expression of the luciferase gene to a similar degree, except for the Ialpha4 promoter, which had much higher activity. Also the degree to which TGF-beta induced GL expression of the various isotypes in 55D1 B cells did not reflect in vivo expression. However, most of the TGF-beta-stimulated cells expressed GL mRNA of multiple isotypes; no isotype was expressed preferentially. These results suggest that the final switch to a single isotype is regulated in a step subsequent to GL transcription, rather than by induction of GL transcripts by the Ialpha promoter.

A single 3' alpha hs1,2 enhancer in the rabbit IgH locus

Multiple cis-acting elements including the intronic enhancer and the 3'alpha enhancer (3'alphaE) regulate expression of the Ig heavy chain genes during B cell development. A 3'alphaE is composed of DNase I-hypersensitive sites, hs1,2, hs3a,b, and hs4, found 3' of the murine Calpha gene as well as 3' of both human Calpha genes, Calpha1 and Calpha2. Rabbits have 13 Calpha genes, and we tested whether a 3'alphaE is associated with each of these genes. To identify 3'alphaE regions we developed a rabbit hs1,2 probe and used this to search for enhancer homologues of human hs1,2 in a genomic fosmid library. We identified a single hs1,2 fragment 8-kb downstream of Calpha13, the presumed 3'-most Calpha gene. We also identified and partially sequenced a new Calpha gene, Calpha14, located 6 kb upstream of Calpha13. Genomic Southern blot analysis confirmed that the rabbit genome contains only one hs1,2 enhancer region. We tested the enhancer activity of the hs1,2 with the SV40, V(H), and Ialpha promoters using the luciferase reporter gene in transient transfection assays and found that it significantly enhanced the activity of SV40 and V(H) promoters and slightly enhanced an Ialpha promoter. We conclude that the rabbit has a single hs1,2 enhancer that resides at the 3' end of the IgH gene cluster and may constitute one of the cis-elements regulating the expression of IgH genes.

B Lymphocyte Selection and Age-Related Changes in VH Gene Usage in Mutant Alicia Rabbits

Young Alicia rabbits use VHa-negative genes, VHx and VHy, in most VDJ genes, and their serum Ig is VHa negative. However, as Alicia rabbits age, VHa2 allotype Ig is produced at high levels. We investigated which VH gene segments are used in the VDJ genes of a2 Ig-secreting hybridomas and of a2 Ig+ B cells from adult Alicia rabbits. We found that 21 of the 25 VDJ genes used the a2-encoding genes, VH4 or VH7; the other four VDJ genes used four unknown VH gene segments. Because VH4 and VH7 are rarely found in VDJ genes of normal or young Alicia rabbits, we investigated the timing of rearrangement of these genes in Alicia rabbits. During fetal development, VH4 was used in 60–80% of nonproductively rearranged VDJ genes, and VHx and VHy together were used in 10–26%. These data indicate that during B lymphopoiesis VH4 is preferentially rearranged. However, the percentage of productive VHx- and VHy-utilizing VDJ genes increased from 38% at day 21 of gestation to 89% at birth (gestation day 31), whereas the percentage of VH4-utilizing VDJ genes remained at 15%. These data suggest that during fetal development, either VH4-utilizing B-lineage cells are selectively eliminated, or B cells with VHx- and VHy-utilizing VDJ genes are selectively expanded, or both. The accumulation of peripheral VH4-utilizing a2 B cells with age indicates that these B cells might be selectively expanded in the periphery. We discuss the possible selection mechanisms that regulate VH gene segment usage in rabbit B cells during lymphopoiesis and in the periphery.

In Vitro Induction of the Expression of Multiple IgA Isotype Genes in Rabbit B Cells by TGF-β and IL-2

The rabbit genome has 13 different Cα genes that are expressed at different levels in mucosal tissues. To analyze the factors involved in the differential expression of these Cα genes, we cloned and sequenced the promoters of the Iα regions that control the expression of sterile mRNA. We found that all Cα genes, including Cα3 and Cα8, which are not expressed, and Cα4, which is expressed at high levels, have similar nucleotide sequences in the Iα region, and all contain the recognition elements for TGF-β in the promoter. B lymphocytes from popliteal lymph nodes or Peyer’s patch activated in vitro could be induced by TGF-β to express sterile IgA transcripts of all IgA isotypes, except Cα2, Cα3, and Cα8. Many single B lymphocytes transcribed sterile mRNA of more than one IgA isotype, which demonstrates that transcription of sterile mRNA alone does not regulate the IgA isotype switch. The addition of IL-2 led to the expression of transcripts of mature IgA of all isotypes, except Cα2, Cα3, and Cα8. The predominantly expressed isotype in these experiments was Cα4. With the use of an IgA4-specific mAb we found that IgA4+ plasma cells are unevenly distributed throughout the small intestine such that many of the IgA+ plasma cells in the duodenum-jejunum produced IgA4, whereas in the lower part of the ileum IgA4-producing cells were almost absent. Because the microbial flora varies throughout the intestine, we suggest that the microbial flora creates different local environments and thus affects either isotype switching or homing of IgA-expressing cells.

Thiol-disulfide redox buffers maintain a structure of immunoglobulin A that is essential for optimal in vitro binding to secretory component

We have shown that human secretory component (SC) binds in vitro to different samples of human and murine dimeric immunoglobulin A (IgA). The binding ratio in the IgA/SC complex is 1:1. IgA which is stably bound to SC is separated from unreacted IgA by anion exchange chromatography. A part of IgA/SC complexes formed in vitro is unstable to this elution; the proportion varies between different samples of IgA; it increases following prolonged incubation of IgA at 37 degrees C. Incubation of IgA with glutathione/glutathione disulfide (GSH/GSSG) redox buffers increases the proportion able to form a stable complex with SC to approximately 90%. The presence of bound SC is not essential for this process but does allow it to occur at a lower GSH/GSSG concentration. The stable IgA/SC complex consists of a structure with a disulfide bond between IgA and SC apparently in equilibrium with a structure in which this bond is absent. The proportion bound covalently is similar for different samples of IgA and is insensitive to incubation with GSH/GSSG. It is significantly greater for secretory IgA (sIgA) and for IgA and SC incubated together with a starting mixture of cysteine/cystine. Monoclonal, antigen-specific IgA, all of which is optimally bound to SC in essentially the same way as in native sIgA, can be isolated in high yield. Our results support a mechanism for optimal binding of IgA to SC, that can occur both in vitro and in vivo, in which a thiol disulfide interchange occurs between a free IgA thiol and a sensitive SC disulfide following the initial non-covalent interaction.

Trans-chromosomal recombination within the Ig heavy chain switch region in B lymphocytes

Somatic DNA rearrangements in B lymphocytes, including V(D)J gene rearrangements and isotype switching, generally occur in cis, i. e., intrachromosomally. We showed previously, however, that 3 to 7% of IgA heavy chains have the VH and Calpha regions encoded in trans. To determine whether the trans-association of VH and Calpha occurred by trans-chromosomal recombination, by trans-splicing, or by trans-chromosomal gene conversion, we generated and analyzed eight IgA-secreting rabbit hybridomas with trans-associated VH and Calpha heavy chains. By ELISA and by nucleotide sequence analysis we found that the VH and Calpha regions were encoded by genes that were in trans in the germline. We cloned the rearranged VDJ-Calpha gene from a fosmid library of one hybridoma and found that the expressed VH and Calpha genes were juxtaposed. Moreover, the juxtaposed VH and Calpha genes originated from different IgH alleles. From the same hybridoma, we also identified a fosmid clone with the other expected product of a trans-chromosomal recombination. The recombination breakpoint occurred within the Smicro/Salpha region, indicating that the trans-association of VH and Calpha genes occurred by trans-chromosomal recombination during isotype switching. We conclude that trans-chromosomal recombination occurs at an unexpectedly high frequency (7%) within the IgH locus of B lymphocytes in normal animals, which may explain the high incidence of B-cell tumors that arise from oncogene translocation into the IgH locus.

Production of secretory immunoglobulin A by a single mammalian cell

Secretory IgA (sIgA) plays a critical role in providing protection against infection at the mucosal surfaces. Normally, sIgA is the product of two different cell types with heavy, light, and J chains produced by the plasma cells, whereas secretory component (SC), a cleavage product of the polymeric immunoglobulin receptor (pIgR), is added during the transit of dimeric IgA through the epithelial cell layer. In the current study, by introducing a gene for the processed form of SC into a cell line that produces dimeric IgA, we have succeeded in creating a single cell that is able to produce and secrete covalently joined sIgA. To our knowledge, this is the first time it has been possible to efficiently produce large quantities of sIgA of defined specificity in mammalian cells. The sIgA made using this approach has great potential as an immunotherapeutic.

Generation and assembly of secretory antibodies in plants

Four transgenic Nicotiana tabacum plants were generated that expressed a murine monoclonal antibody kappa chain, a hybrid immunoglobulin A-G heavy chain, a murine joining chain, and a rabbit secretory component, respectively. Successive sexual crosses between these plants and filial recombinants resulted in plants that expressed all four protein chains simultaneously. These chains were assembled into a functional, high molecular weight secretory immunoglobulin that recognized the native streptococcal antigen I/II cell surface adhesion molecule. In plants, single cells are able to assemble secretory antibodies, whereas two different cell types are required in mammals. Transgenic plants may be suitable for large-scale production of recombinant secretory immunoglobulin A for passive mucosal immunotherapy. Plant cells also possess the requisite mechanisms for assembly and expression of other complex recombinant protein molecules.

Generating the antibody repertoire in rabbit

We describe a model for B cell development and generation of the antibody repertoire in rabbits. In this model, B cells develop early in ontogeny, migrate to GALT, and undergo the first round of diversification by a somatic gene conversion-like process and by somatic mutation. We designate the repertoire developed by this mechanism as the primary antibody repertoire and it is this repertoire that makes the rabbit immunocompetent. We invoke GALT as the site for development of the primary repertoire because (1) surgical removal of GALT from neonatal rabbits results in highly immunocompromised animals, (2) in germfree rabbits essentially no lymphoid development occurs in GALT and the rabbits are immunoincompetent, and (3) the follicular development of rabbit GALT is highly similar to that of the chicken bursa, the site in which the primary antibody repertoire develops by somatic gene conversion in chicken. We suggest that once the primary antibody repertoire is formed, it is maintained by self-renewing CD5+ B cells and is expanded to a secondary antibody repertoire after the B cells encounter antigen.

Comparative mapping of IGHG1, IGHM, FES, and FOS in domestic cattle

The immunoglobulin genes have not been genetically characterized as thoroughly in cattle as in other mammals, particularly humans and mice. Comparative gene mapping in mammals suggests that the bovine immunoglobulin heavy chain genes, IGHG4 and IGHM might be syntenic with the FOS oncogene. Interestingly, however, when these genes were assigned to bovine syntenic groups utilizing a panel of bovine: hamster hybrid somatic cells, IGH genes were shown to be syntenic with the FES oncogene rather than FOS. In this study IGH and FES were assigned to Bos taurus chromosome 21 while FOS was assigned to chromosome 10. In addition, bovine-specific immunoglobulin-like sequences were observed in the hybrid somatic cells, and one, IGHML1, was mapped to bovine syntenic group U16. The probes used for somatic-cell mapping were also used to screen a small number of cattle of several different breeds for restriction fragment length polymorphisms. IGHG4 and IGHM were shown to be highly polymorphic, while FOS and FES were not.