Cloning and characterization of cDNAs encoding four different canine immunoglobulin γ chains

cDNAs encoding four different canine immunoglobulin G (caIgG) gamma chains were identified in this study. One of these IgG gamma chain cDNAs, (caIgG-A), represents 92.5% of the IgG gamma chain cDNAs in a dog spleen cell cDNA library; a second partial IgG gamma chain cDNA (caIgG-B) was also identified in the library. The other two IgG gamma chain cDNAs (caIgG-C and caIgG-D) were RT-PCR amplified from canine lymphoma samples. Comparison of the four different canine IgG gamma chain cDNAs showed homologies from 83.6 to 89.2% and from 73.1 to 81.8% at nucleotide and amino acid sequence levels, respectively. Despite the high similarity in CH1, CH2 and CH3 domains among the different caIgG gamma chains, the hinge regions were distinct, sharing only 19.0-35.2% homology at the amino acid level. No multiple duplication of the hinge region, as reported for human IgG1 and IgG3, was detected in any of the canine IgG gamma chains. The numbers of cysteines in the putative hinge regions were found to be 3, 2, 7 and 3 for the four canine IgG heavy gamma chains (A, B, C and D), respectively. Specific primers were designed based on caIgG gamma chain hinge region DNA sequences and were used in RT-PCR for measuring different caIgG gamma chain mRNA levels in canine PBMC samples.