The author has opted for this paper to be made Open Access after print publication; therefore the print version is still reflective of a non-Open Access publication.. discovery of antibodies over a century ago, early studies in the horse made important contributions to the understanding of the mammalian adaptive immune system. However, large gaps still remain in our knowledge of the equine immunoglobulin (Ig) system and this is hampering development of specific vaccines and immune-based therapies for many major infectious diseases of the horse. Given the economic importance of the horse globally, it is vital to build a more detailed understanding of equine Ig function, as a key first step toward more effective options for treatment and prevention of equine diseases. A better understanding of the equine IgA (eqIgA) system would seem especially important given the numerous equine infections that are manifest in, or gain a Amodiaquine hydrochloride foothold at, the mucosal surface.1 In addition, a wider knowledge of IgA systems in different mammals will provide invaluable insights into both the variety of functions mediated by this Ab class, and the evolution of the IgA system. Moreover, because there are limitations with mouse models of the IgA system (e.g., the mouse lacks the main Fc receptor (FcRI) responsible for IgA effector function), it is worthwhile developing a wider knowledge of the IgA systems of other mammals so that relevant animal UKp68 models may be identified. For these reasons, we sought to establish systems to facilitate molecular characterization of eqIgA. IgA is present in both the serum and mucosal secretions of the horse, and it is the principal Ig in milk, tears, and secretions of the upper respiratory tract.2 In common with most other Amodiaquine hydrochloride mammalian species, the horse has a single IgA heavy chain constant region gene (chromosome 3 (ECA3) and ECA5, respectively. Human and mouse J chain and genes have been localized to HSA4 (chromosome 4) and MMU5 (chromosome 5) and HSA1 and MMU1, respectively.19, 20, 21, 22 Comparative mapping of the human, mouse, and equine genomes has aligned regions of HSA4 and MMU5 to ECA3 and regions of HSA1 and MMU1 to ECA523, 24 providing support for our assignment of the equine genes. Close to the human gene on chromosome 1q31Cq42 are the Fc receptors for IgG (FcR), IgE (Fc?RI), and IgA/IgM (Fc/R). We located a receptor homologous to human and mouse Fc/R (accession no. “type”:”entrez-nucleotide”,”attrs”:”text”:”XM_001489848″,”term_id”:”149708015″,”term_text”:”XM_001489848″XM_001489848) downstream of genes bear a close resemblance to those of human and mouse,22, 25, 26, 27 with the coding sequence of J chain distributed across 4 exons and that of pIgR across 11 exons (Figure 8). Open in a separate Amodiaquine hydrochloride window Figure 8 Gene organization. Structure of the (a) equine J chain and (c) pIgR genes, and comparison of (b) equine J chain and (d) pIgR exonCintron boundaries with those of the human and mouse genes. Equine J chain coding sequence is arranged as follows: exon 1, 97?bp encoding 33?bp untranslated region (UTR) and the first 21 residues of the leader peptide; exon 2, 126?bp encoding the last amino acid of the leader peptide and amino acids +1C41; exon 3, 81?bp encoding amino acids 42C68; and exon 4, 1.1?kb encoding amino acids 69C136 (205?bp) and a long 3 UTR. Equine polymeric Ig receptor (pIgR) coding sequence is arranged as follows: exon 1, 128?bp of 5 UTR; exon 2, 97?bp encoding 5 UTR and 14 amino acids of the leader peptide; exon 3, encodes 4 amino acids of the leader peptide and all of D1; exon 4, encodes D2 and D3; exon 5, encodes D4; exon 6, encodes D5; exon 7 encodes D6;.