A comprehensive analysis of immunoglobulin heavy chain genes in the Bactrian camel ( Camelus bactrianus )

Heavy chain only antibodies (HCAbs) represent a rare type of antibody that is devoid of light chains and the CH1 domain that have been reported in cartilaginous fish and camelids. By analyzing transcript data and genome sequences, we conducted a comprehensive analysis of Bactrian camel immunoglobulin heavy chain genes. Based on the transcript data, one mu gene, five gamma genes, one alpha gene and one epsilon gene were found. Additionally, the variable region of HCAbs (VHH) and the conventional antibodies (VH) sequences associated with the gamma 3, gamma 1a/b and mu genes were amplified. Based on these genome sequences, seven DH, six JH, mu, gamma 2a, gamma 2c, alpha, and epsilon genes and a portion of a gamma 3 gene were observed. Different Kozak sequences within different VH families were found in our analysis, and the variability index differed between the VHH3 and VH3 families. Phylogenetic analysis of the constant regions of the camelid immunoglobulin genes indicates that these genes appeared before the evolutionary divergence of Bactrian camels and dromedaries.