To investigate an association of macrophage-derived chemokine (MDC/CCL22) in immunopathogenesis of atopic dermatitis (AD) in dogs, canine MDC cDNA was cloned and its mRNA expression was examined in lesional and non-lesional skin of dogs with AD.

Canine macrophage-derived chemokine cDNA was cloned from a dog thymus by RT-PCR with rapid amplification of cDNA ends (RACE) method. To examine the expression of MDC mRNA in normal tissues and skin (lesional and non-lesional) of dogs with AD (N=5), RT-PCR was performed using total RNA samples extracted from these tissues. Together with expression of MDC mRNA, expression of TARC mRNA was also evaluated in the same skin samples obtained from dogs with AD.

The canine MDC cDNA showed 73.1%, 68.8% and 68.8% amino acid sequence similarities with human, mouse and rat homologues, respectively. In normal dog tissues, expression of MDC mRNA was detected not only in thymus but also in spleen, lymph node, lung and heart. Although TARC mRNA was detected in the lesional skin but not in the non-lesional skin in 5 dogs with AD, MDC mRNA was detected in both lesional and non-lesional skin in 1 of the 5 dogs with AD.

The present study indicated that the expression pattern of MDC was similar to that of TARC in normal tissues but was different from that of TARC in the skin of dogs with AD, suggesting that MDC may be less important in the immunopathogenesis of canine AD than TARC.