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Review
, 30 (1-2), 93-100

Immunoglobulins of the Non-Galliform Birds: Antibody Expression and Repertoire in the Duck

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Review

Immunoglobulins of the Non-Galliform Birds: Antibody Expression and Repertoire in the Duck

Mats L Lundqvist et al. Dev Comp Immunol.

Abstract

Galliform and non-galliform birds express three immunoglobulin isotypes, IgM, IgA and IgY. Beyond this we should not generalize because differences in gene organization may have functional consequences reflected in the immune response. At present, studies on non-galliform birds are largely restricted to ducks. Ducks express an alternatively spliced form of their IgY heavy chain (upsilon) gene, the IgY(DeltaFc), that lacks the Fc region and Fc-associated secondary effector functions. It is not known how common the expression of the IgY(DeltaFc) is among birds, nor the functional consequences. It is also not known whether the unusual organization of the duck IgH locus, also shared with the chicken, having the gene order of mu, alpha and upsilon, with alpha inverted in the locus, is unique to the galloanseriform lineage. Ducks, like chickens, have a single immunoglobulin light chain of the lambda (lambda) type. Evidence suggests that ducks, like chickens, generate their immunoglobulin repertoire through a single functional rearrangement of the variable (V) region, and generate diversity through gene conversion from a pool of pseudogenes. In Southern blots of germline and rearranged bursal DNA, both the heavy and light chain loci of ducks appear to each undergo one major rearrangement event. For both heavy and light chains, the functional V region element and the pseudogenes appear to consist of a single gene family. Further analysis of 26 heavy chain joining (JH) and 27 light chain JL segments shows there is use of a single J segment in ducks, which is diversified presumably through somatic mutations and gene conversion events. Despite this limitation on the rearrangement of immunoglobulin genes, analysis of 26 DH and 122 VL sequences suggests that extensive sequence diversity is generated.

Figures

Fig. 1
Fig. 1
A schematic of the structures of duck antibodies. The polymeric structures of duck IgM and IgA have not been directly determined but inferred from size estimates of the intact molecules and their constituent polypeptide chains (see discussion in text).
Fig. 2
Fig. 2
A schematic of the duck immunoglobulin heavy chain locus. The D region through the three C region genes has been completely sequenced on overlapping lambda phage clones. The number of functional V and D elements is inferred and the number of pseudo V region genes is unknown. Below the locus are schematics of the heavy chain transcripts to illustrate the alternative transcripts arising from each gene, giving rise to the heavy chains for the secreted and membrane bound immunoglobulins.
Fig. 3
Fig. 3
Frequency of percent sequence identity in pairwise comparisons of 26 duck JH segments (A) and 26 duck DH segments (B). The data were derived from a multiple alignment of the sequences of 26 cDNA clones isolated from a single duck. Sequences were aligned using Clustal W (Megalign, DNAStar, Madison WI) and the J regions and D regions identified by comparison. Individual JH region sequences and individual DH region sequences were compared to each other generating 325 pairwise comparisons.
Fig. 4
Fig. 4
Restricted rearrangements of the IgH (A) and IgL (B) loci of the duck. Approximately 10 μg of DNA in germline organization extracted from nucleated erythrocytes (G) and DNA in rearranged organization extracted from Bursa of Fabricius (B) was digested with the restriction enzymes shown and subjected to Southern Blot analysis. Schematics of the IgH and IgL loci below the Southern blots indicate the locations of the probes used. The number of functional VH and DH segments, and the number of functional V and J segments are not known, but are inferred from the Southern blot analysis.
Fig. 5
Fig. 5
Frequency of percent identity in pairwise comparisons of 121 VL (A) and 27 JL (B) segments. The sequences were aligned using Clustal W (Megalign, DNAStar, Madison WI), and sequences corresponding to individual VL and JL regions were separated. Comparison of individual sequences was done for 121 VL and 27 JL sequences yielding 7260 and 351 pairwise comparisons, respectively. A cDNA library constructed from duck spleen [45] was once amplified, plasmids excised from lambda ZAP in bulk, and individual bacterial colonies randomly selected. Single-pass sequences of cDNA clones used in the analysis of heavy and light chains are deposited in the Genbank dbEST database under accession numbers CX95445-581 and DN161074-85.

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