B6-Igl Knockout Mice: Research Model for B Cell Development & Antibody Diversity

Introducing the B6-Igl KO Mouse Model: An Innovative Knockout Mouse for B Cell and Antibody Research

The novel B6-Igl Knockout (KO) mouse model exclusively expresses κ light chain immunoglobulins, offering researchers a powerful tool for exploring B cell development and antibody diversity. This Igl KO mouse model on the B6 strain background is specifically engineered to delete the λ light chain gene segments, allowing for focused study on the role of κ light chains in immune responses, autoimmune diseases, and immunoglobulin diversity. With its unique genetic profile, the B6-Igl KO mouse model provides invaluable insights for advancing antibody-based research and therapeutic discovery. Dive into the features and applications of this groundbreaking knockout mouse model, optimized for both preclinical and biomedical research in immunology.

Immunoglobulins (Ig): Key Components in Antibody Activity

Immunoglobulins (Ig) are large “Y”-shaped glycoprotein molecules which exhibit antibody activity or structures similar to antibodies which are used by the immune system to identify and neutralize antigens. Immunoglobulins are classified into two types: secreted (soluble) and membrane-bound forms (which contain a hydrophobic transmembrane region). Membrane-bound immunoglobulins (mIg) are part of the B-cell antigen receptor (BCR) complex on the B cell surface, primarily responsible for recognizing antigens and aiding in B cell activation and differentiation. Secreted immunoglobulins (sIg), also known as antibodies (Ab), are primarily found in serum and body fluids. These antibodies are produced by plasma cells (differentiated from B cells), and are capable of specific binding to antigens and mediating immune responses.

Structurally, Igs consist of two identical light chains and two identical heavy chains.^[1-2]  Mammals produce two types of light chains, kappa (κ) and lambda (λ), but individual B cells express only one kind. The newly introduced B6-Igl Knockout Mouse is a model that achieves knockout (KO) of the λ light chain to specifically express κ chain immunoglobulins.

Figure 1. Schematic Diagram of the Structure and Types of Immunoglobulin (Ig) Molecules. ^[2]

Immunoglobulin Gene Rearrangement and Antibody Diversity

Immunoglobulins (Ig) are composed of two identical light chains (L) and two identical heavy chains (H), forming a classic Y-shaped structure through interchain disulfide bonds and non-covalent interactions, with a flexible hinge region joining them.^[3-4] Each heavy and light chain contains a variable region and a constant region, with the variable region responsible for recognizing and binding to specific antigens. Antibody diversity primarily arises from the sequence differences in these variable regions, enabling B cells to recognize countless different antigens. Although they are functionally similar, a single mammalian B cell can express only one type of light chain, either κ or λ. The κ-to-λ chain ratio varies across species. In humans, the κ-to-λ ratio is approximately 2:1; whereas in mice, this ratio is about 20:1, with most mouse B cells expressing the κ light chain.^[5] 

The variable region diversity is further enhanced through the immunoglobulin rearrangement process, also known as V(D)J recombination, where the genes that encode the B-cell receptor are rearranged to create unique immunoglobulins. The gene segments encoding antibodies (Ig gene loci) consist primarily of a variable region (V) and a constant region (C). The highly variable V region includes the variable (V) gene, diversity (D) gene, and joining (J) gene, which are linked through random DNA rearrangements and then joined with the relatively conserved constant (C) region to encode different types of antibodies.^[6]

Figure 2. Rearrangement of Immunoglobulin (Ig) Heavy and Light Chain Gene Loci Produces Antibodies and BCRs with Different Antigen Specificities.^[7]

The Role of the λ Light Chain in B Cell Development and Disease

During B cell development, functional B cell receptors (BCRs) are generated through gene rearrangement. B cells preferentially rearrange the κ light chain gene, with the λ light chain (Igλ) serving as an alternative to the κ light chain (Igκ). This mechanism ensures that even if Igκ rearrangement fails, B cells can still produce functionally diverse antibodies, which is critical for maintaining the antibody repertoire.^[8-10] As part of the BCR, Igλ can bind specific antigens, promoting B cell activation and differentiation into plasma and memory B cells. Abnormal rearrangement or dysfunction of Igλ expression can lead to autoimmune diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis, and is also associated with B cell malignancies like multiple myeloma and light chain amyloidosis (AL amyloidosis).^[11-13] Furthermore, Igλ chain deletions or abnormalities are linked to conditions  characterized by low immunoglobulin levels and increased susceptibility to infections. such as hypogammaglobulinemia, common variable immunodeficiency (CVID), and primary immunodeficiency diseases (PIDD).^[14-16]

Figure 3. Process of Immunoglobulin (Ig) Rearrangement During B Cell Development. ^[10]

Developing the B6-Igl KO Mouse Model

Both the λ light chain and κ light chain gene loci lack D genes and contain only V, J, and C gene segments. Cyagen has developed the B6-Igl KO Mouse (Product No.: C001550) by using gene-editing technology to knock out all gene sequences encoding the V, J, and C regions within the mouse λ light chain gene locus (Igl). As a result, this mouse model no longer expresses the λ light chain, with B cells specifically expressing only the κ light chain. Below are the details of this model.

Figure 4. Gene Knockout Strategy Diagram for B6-Igl KO Mouse.

Igλ and Igκ Expression in B Cells

Results indicate that in wild-type mice, B cells primarily express the κ light chain (Igκ), with a small subset of B cells expressing the λ light chain (Igλ). In contrast, due to the knockout of the λ light chain (Igl) gene locus in B6-Igl KO mice, B cells exclusively express the κ light chain (Igκ), with no λ light chain expression detected.

Figure 5. Proportion of B Cells Expressing Immunoglobulin λ Light Chain (Igλ) or κ Light Chain (Igκ) in the Spleen and Bone Marrow of Wild-Type and B6-Igl KO Mice.

Model Summary and Research Applications

With the deletion of the λ light chain gene locus (Igl), B cells in B6-Igl KO mice (Product No.: C001550) express only κ light chain immunoglobulins. Therefore, this model can be used to generate mouse antibodies containing only the κ light chain, to study the role of the λ light chain in B cell development and function, and to analyze the mechanisms involving the λ light chain in specific immune responses or autoimmune diseases. This model offers potential for exploring antibody diversity, immune system regulation, and potential therapeutic approaches.

B6-Igl KO mice can be crossed with humanized light chain mouse models to develop mice that express human-specific light chains, enabling the generation of fully human antibodies for research and therapeutic development. Alternatively, other types or species-specific antibody sequences can be inserted into the mouse model for in vivo studies in cases where mouse antibody sequences are absent.

Cyagen has developed various genetic disease models, inducible disease models, target humanized models, and fully human antibody mouse models in the fields of immunology and human antibody research. These models provide researchers with powerful tools for developing targeted therapies and antibody drugs for various diseases.

Humanized Target Gene Disease Models

Cyagen’s Next-Generation Humanized Mouse Models: HUGO

Cyagen has launched the HUGO (Humanized Genomic Ortholog) Project, inviting global partners to collaborate on developing novel fully humanized models to support new drug development.

HUGO-GT™ Next-Generation Humanized Models

The Humanized Genomic Ortholog for Gene Therapy (HUGO-GT™) mouse model offers a higher degree of humanization compared to traditional models to serve as an effective evaluation platform, especially for gene therapy drugs with high requirements for gene sequence integrity, such as ASO, CRISPR, and siRNA.

Our HUGO-GT^TM fully humanized genome mice are developed based on the proprietary TurboKnockout-Pro technology to achieve in situ replacement of mouse genes, encompassing a broader range of intervention targets and providing full coverage of pathogenic gene mutation sites-all without patent or ownership disputes. The fully humanized target genes within these models are consistent with the pathogenic genes carried by humans and cover the majority of drug targets, significantly enhancing screening efficiency for various types of preclinical drug experiments.

HUGO-Ab™ Mice for Fully Human Antibody Discovery

HUGO-Ab^TM (HUmanized Genomic Ortholog for Antibody Development) mice represent a leap forward in antibody discovery models:  with fully humanized genes in the antibody variable regions, these mice are capable of producing fully humanized antibodies in vivo with high affinity and low immunogenicity. Our TurboKnockout® ES technology replaces the VH and VL genes in situ to offer a higher degree of humanization with more stable phenotypic and functional outcomes in progeny than traditional transgenic methods.

HUGO-Ab™ Mouse Models for Antibody Discovery

* Fully human, full sequence diversity (Heavy, kappa, Lambda)

* Robust immune response for efficient discovery

* Human-like immune profile for vaccine development

* Numerous fixed light chain models

* Single domain models for monobody discovery

* Multiple backgrounds (B6, Balb/c, SJL)

High-throughput Fully Humanized Antibody Discovery Platform

Combining Biointron’s AbDrop™ with Cyagen’s HUGO-Ab™ mice streamlines the discovery of fully human antibodies to as few as 3 months. Our innovative High-throughput Fully Humanized Antibody Discovery Platform simplifies and accelerates drug development by eliminating the need for complex genetic modifications,  reducing costs, and leading to safer, more effective antibody therapies.

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