Expression of individual immunoglobulin genes occurs in an unusual system consisting of multiple independent loci

Eason, Donna D.; Litman, Ronda T.; Luer, Carl A.; Kerr, William G.; Litman, Gary W.

doi:10.1002/eji.200425224

Cited by 34 publications

(25 citation statements)

References 41 publications

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“…This process may involve a spatial component (''compartment''), in that the time before the RAGs are down-regulated would be sufficient to rearrange another gene in the locus because it would be in close proximity. The observation that other species with multiple loci on the same chromosome have more cells expressing two Abs (38) supports this argument. Alternatively multiple rearrangements may take place at the same time.…”

Section: Discussionmentioning

confidence: 55%

Generation of heavy-chain-only antibodies in mice

Janssens¹,

Dekker²,

Hendriks

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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We have generated transgenic mice containing hybrid llama͞ human antibody loci that contain two llama variable regions and the human D, J, and C and͞or C␥ constant regions. Such loci rearrange productively and rescue B cell development efficiently without LC rearrangement. Heavy-chain-only antibodies (HCAb) are expressed at high levels, provided that the CH1 domain is deleted from the constant regions. HCAb production does not require an IgM stage for effective pre-B cell signaling. Antigenspecific heavy-chain-only IgM or IgGs are produced upon immunization. The IgG is dimeric, whereas IgM is multimeric. The chimeric HCAb loci are subject to allelic exclusion, but several copies of the transgenic locus can be rearranged and expressed successfully on the same allele in the same cell. Such cells are not subject to negative selection. The mice produce a full antibody repertoire and provide a previously undescribed avenue to produce specific human HCAb in the future.immunoglobulin rearrangement ͉ transgenic C onventional antibodies contain two heavy and light chains (LC) coded for by heavy and LC loci. B cell development and antibody production starts in the bone marrow (BM) by heavy chain (HC) VDJ recombination and expression of IgM associated with a surrogate LC on the cell surface. In a second round of recombination, one of the LC rearranges in pre-B cells. If successful, the B cells undergo selection, affinity maturation, and switching to different HC constant regions to result in B cells, which express tetrameric antibodies of different isotypes (IgA, IgG, and IgE). Normally absence of HC or LC expression leads to arrest of B cell development. However, some species produce HC-only antibodies (HCAb) as part of their normal B cell development and repertoire. The best-known HCAb (i.e., no LC) are IgG2 and IgG3 in camelids (1). They undergo antigen-mediated selection and affinity maturation, and their variable domains are subject to somatic hypermutation (2, 3). HCAb are thought to recognize unusual epitopes, such as clefts on the antigen surface (4). The first domain of the constant region, CH1, is spliced out because of the loss of a consensus splice signal (5, 6). CH1 exon loss also has been described in other mammals, albeit associated with disease, e.g., in mouse myelomas (7) and human HC disease (HCD) (8-10).Camelid HCAbs contain a complete VDJ region. Its size, stability, specificity, and solubility have generated considerable biotechnological interest. The antigen-binding site, a single-variable domain (VHH), resembles VH of conventional Abs. However, differences in FR2 and CDR3 prevent VHH to pair with a variable LC, whereas hydrophilic amino acids provide solubility (11). HCAb of the IgM class have not been found in camelids, suggesting that the IgM ϩ stage of HCAb formation is very transient and͞or circumvented.Murine NSO myeloma cells can express a rearranged camelid VHH-␥2a gene (12) and, recently, the same gene was expressed in transgenic mice (13). Here, we describe transgenic mice containing various...

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Section: Discussionmentioning

confidence: 55%

Generation of heavy-chain-only antibodies in mice

Janssens¹,

Dekker²,

Hendriks

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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“…Moreover, tetrameric and homodimeric IgGs differ in their V regions (so-called V H and V H H regions, respectively), which are encoded by a distinct set of V genes (8,9). V H and V H H regions have the same general structure made up of four framework regions (FR) 2 and three complementarity-determining regions or CDRs; however, V H H regions display, in their FR2, several hydrophilic substitutions of amino acids highly conserved across species (i.e., Val 42 to Phe or Tyr, Gly 49 to Glu, Leu 50 to Arg or Cys, and Trp 52 to Gly or Phe) (5,10,11). These hydrophilic amino acid substitutions in the V H H together with the absence of the first constant domain in the C H H region may explain the lack of pairing of homodimeric IgH to L chains.…”

Section: Tetrameric and Homodimeric Camelid Iggs Originate From The Smentioning

confidence: 99%

Tetrameric and Homodimeric Camelid IgGs Originate from the Same IgH Locus

Achour

Cavelier

Tichit

et al. 2008

The Journal of Immunology

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In addition to producing conventional tetrameric IgGs, camelids have the particularity of producing a functional homodimeric IgG type lacking L (light) chains and only made up of two H (heavy) chains. This nonconventional IgG type is characterized by variable and constant regions referred to as VHH and CHH, respectively, and which differ from conventional VH and CH counterparts. Although the structural properties of homodimeric IgGs have been well investigated, the genetic bases involved in their generation are still largely unknown. In this study, we characterized the organization of genes coding for the H chains of tetrameric and homodimeric IgGs by constructing an alpaca (Lama pacos) genomic cosmid library. We showed that a single IgH locus in alpaca chromosome 4 contains all of the genetic elements required for the generation of the two types of Igs. The alpaca IgH locus is composed of a V region that contains both VHH and VH genes followed by a unique DH-JH cluster and C region genes, which include both CHH and CH genes. Although this general gene organization greatly resembles that of other typical mammalian Vn-Dn-Jn-Cn translocon IgH loci, the intermixed gene organization within the alpaca V and C regions reveals a new type of translocon IgH locus. Furthermore, analyses of cDNA coding for the membrane forms of IgG and IgM present in alpaca peripheral blood B cells are most consistent with the notion that the development of a B cell bearing homodimeric IgG passes through an IgM+ stage, similar to the case for conventional IgG.

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“…Somatic hypermutation of immunoglobulin genes, which is a central feature of BCR maturation, occurs in the earliest extant jawed vertebrates -the cartilaginous fish 52,53 -and might be an accentuation of a genome-wide process 54,55 . ALLELIC EXCLUSION of BCR-and TCR-gene loci, which is an integral component of single-cell immune commitment that is present throughout jawed-vertebrate phylogeny 56 , is also a feature of the loci encoding olfactory receptors 57,58 and protocadherins 59 , emphasizing again the integration of pre-existing mechanisms in the evolution of immunity. The full potential of these features did not come to fruition until the co-evolution of mechanisms to select and expand individual clones of immune cells.…”

Section: Transitions From Innate To Adaptive Immunitymentioning

confidence: 99%

Reconstructing immune phylogeny: new perspectives

2005

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Numerous studies of the mammalian immune system have begun to uncover profound interrelationships, as well as fundamental differences, between the adaptive and innate systems of immune recognition. Coincident with these investigations, the increasing experimental accessibility of non-mammalian jawed vertebrates, jawless vertebrates, protochordates and invertebrates has provided intriguing new information regarding the likely patterns of emergence of immune-related molecules during metazoan phylogeny, as well as the evolution of alternative mechanisms for receptor diversification. Such findings blur traditional distinctions between adaptive and innate immunity and emphasize that, throughout evolution, the immune system has used a remarkably extensive variety of solutions to meet fundamentally similar requirements for host protection.The evolutionary development of the METAZOANS was associated with the diversification of a wide range of specialized cell-surface molecules that mediate key metabolic processes, as well as provide crucial contact interfaces and carry out a broad range of other essential functions. It is not unexpected that some of these molecules also came to function as barriers to pathogenic invasion and, in doing so, began to carry out dedicated innate immune protective functions. Whereas the simplest form of protection, barrier formation, is essentially mechanical in nature, relentless pressure from genetic variation in pathogens probably drove the evolution of such innate immune protective molecules towards diversification and, in parallel, towards integration of signalling pathways to regulate cellular responses to external stimulation. However, despite the sophistication that such innate immune mediators achieved over time, their biological complexity, by definition, would be limited by genome space, so with increasing complexity of body plan and/or increasing pathogen sophistication, they could be overwhelmed. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptMore than 500 million years ago, a TRANSPOSITION event, probably involving a recombinationactivating gene (RAG)-bearing element, might have given rise to the predecessors of the rearranging antigen-binding receptors of the jawed vertebrates, which encompass the vertebrate radiations that extend from the cartilaginous fish through to humans. This is considered the defining point in the emergence of RAG-mediated (conventional) adaptive immunity 1,2 , which has evolved to create a mechanism for deriving almost limitless variation from very few genes. Studies in traditional and non-traditional animal models, such as sharks, bony fish and birds, have brought this event and its ramifications for host defence into sharper focus. We can now predict much about how these rearranging antigenbinding receptors probably arose, what alternative pathways of immune-receptor gene evolution have occurred, what relationships exist between B-and T-cell-mediated immunity and natural killer (NK)-cell function, how complex immune ...

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Expression of individual immunoglobulin genes occurs in an unusual system consisting of multiple independent loci

Cited by 34 publications

References 41 publications

Generation of heavy-chain-only antibodies in mice

Generation of heavy-chain-only antibodies in mice

Tetrameric and Homodimeric Camelid IgGs Originate from the Same IgH Locus

Reconstructing immune phylogeny: new perspectives

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