Full text loading...
Chapter 7 : Immunoglobulin Genes
Resolution of immunoglobulin structure has revealed how Immunoglobulin molecules can have such great diversity in antigen-binding activities while maintaining conserved effector functions, such as complement activation. IgG is the predominant antibody produced during a secondary immune response. IgG molecules can penetrate extravascular spaces and cross the placental barrier to provide immunity to the fetus. IgA antibodies are the primary antibodies in saliva, tears, and colostrum and in the fluids of the gastrointestinal, respiratory, and urinary tracts. IgM is the predominant class found during a primary immune response. IgD molecules are thought to function as B-cell membrane receptors for antigens and may help in the recruitment of B cells for specific antigen-driven responses. Plasma IgE levels may increase (5 to 20 times the baseline) in parasitic infections and children with atopic diseases. Duplication of an immunoglobulin VH gene(s) results in some haplotypes’ having identical immunoglobulin VH genes belonging to distinct loci, each possibly differing from their respective alleles by one or more nucleotide base substitutions. Immunoglobulin class-switching recombination (CSR) occurs in or near the α switch region upstream of the μ gene and any one of the switch regions of the other heavy-chain isotype genes. Resolution of the junctional sequences in the rearranged immunoglobulin genes expressed by a tumor can provide a specific tumor marker. This marker can be used to examine for any tumor-derived immunoglobulin gene fragments amplified by PCR performed on genomic DNA of lymphoid tissue.
Key Concept Ranking
- Tumor Necrosis Factor alpha
Immunoglobulin heavy-chain gene complex. The heavy-chain exons encoding the constant regions are represented by black boxes, and the associated intronic switch (S) regions are indicated by lines. A ψ next to the heavy-chain isotype designation indicates that the gene is a pseudogene. JH segments and D segments are indicated by lines. Each VH gene locus is labeled on the right of each symbol. Identified polymorphic insertions and/or duplications are indicated with brackets. Black squares represent VH gene loci that are known to be functional. White circles represent VH pseudogenes. At the ends of the line connecting the symbols are arrows that indicate the direction to the centromere or the telomere. The white boxes denote loci that apparently are functional VH genes but that rarely, if at all, are expressed into protein. The arrows indicate the direction of transcription of the gene segments.
Immunoglobulin light-chain gene complexes. The left panel depicts the κ light-chain gene complex on chromosome (Chr) 2p11-12. The black rectangles in this figure represent the Kde or the Cκ constant-region exon as indicated to the right of each rectangle. The Jκ segments are indicated by lines labeled “Jκ.” The κ light-chain enhancer (labeled E) is located between the Jκ segments and the Cκ exon. The Vκ genes that can encode functional κ light-chain variable regions are represented by black boxes, and the Vκ pseudogenes are indicated by white boxes. Immediately adjacent to and to the right of each box is a Roman numeral that denotes the subgroup to which the respective Vκ gene belongs, followed by its designated name. The arrows indicate the direction of transcription of the gene segments. A p is used to label the proximal arm of the Vκ gene complex, and d is used to label the distal arm. The right panel depicts the λ light-chain gene complex on chromosome 22q11.2. The black boxes represent functional Jλ-Cλ exons, whereas white boxes represent Jλ-Cλ pseudogenes. Each of the Jλ-Cλ exon pairs is indicated to the right of each symbol. Each Vλ gene is represented by a black box. To the right of each box is a tentative designation indicating the subgroup (first number) followed by a number indicating the rank order of the particular Vλ in the λ light-chain gene complex. The Vλ genes are organized into three clusters, designated A, B, and C, that are indicated to the left of each cluster. The gene encoding VpreB is located near the C cluster. The direction to the telomere or the centromere is as indicated at the top. The arrows indicate the direction of transcription of the gene segments.
Immunoglobulin gene rearrangement. Diagonal double lines indicate that there is a large distance between flanking genes depicted as rectangular boxes (not drawn to scale). Depicted on the left side of each immunoglobulin gene complex are exemplary immunoglobulin VH genes (VH′, VH″, and VH′″), immunoglobulin κ light-chain genes (Vκ′ Vκ″, and Vκ′″), or immunoglobulin λ light-chain genes (Vλ′, Vλ″, and Vλ′″). D designates the diversity gene segments of the antibody heavy-chain locus. JH, Jκ, and Jλ indicate the joining gene segments of the antibody heavy chain, κ light chain, and λ light chain, respectively. Cμ and Cλ are the constant-region exons of the μ and δ heavy chains, respectively. Below each is a possible immunoglobulin gene rearrangement comprising a VH-D-JH segment for the antibody heavy-chain gene or a Vκ-Jκ or a Vλ-Jλ segment for the κ or λ light-chain gene, respectively. Below the representative λ constant-region loci in row C are listed the names of the lambda nonallelic genetic markers, Mcg, Ke- Oz-, Ke- Oz+, and Ke+ Oz-, on Cλ1, Cλ2, Cλ3, and Cλ7, respectively. As indicated, Cλ4, Cλ5, and Cλ6 are pseudogenes (ψ gene) that do not encode protein.
Schematic representation of the PCR-ELISA technique. Following anchored PCR, a nested PCR attaches a biotin molecule (white box) to the antisense strand of the PCR product. This allows the strand to bind to streptavidin (StrepAv)-coated wells of an ELISA plate. The sense strand is removed by alkaline wash, allowing for hybridization of the tethered antisense strand with digoxigenin-labeled immunoglobulin VH oligonucleotide probes (represented by the ball and stick figures). Hybridized and bound oligonucleotides then are detected using peroxidase-conjugated antidigoxigenin antibodies (anti-digoxigenin peroxidase-conj. Ab). The peroxidase-conjugated antibodies are developed with chromogen, and the plates are read using an ELISA plate reader.
Physical properties of human immunoglobulins
Oligonucleotide primers corresponding to the sense strand of the leader sequences of each of the major V gene subgroups