Evidence of clonal immunoglobulin gene rearrangements in dogs with leishmaniosis

Besides the well-known oncogenic potential of many human and animal viruses chronic bacterial infections sustained by Helicobacter pylori have also been associated with the occurrence of lymphomas in man. Overt lymphoproliferative disorders are known to be the consequence of a multistep process possibly starting with antigenic stimulation with genetic changes occurring subsequently. Intrigued by the description of monoclonal IgM-type cryoglobulinemia associated with Leishmaniosis in human patients and by the observation of a case of persistent IgM monoclonal gammopathy in a dog with Leishmaniosis, in the present study, we have investigated the occurrence of clonal lymphoid expansion by PCR approach in 23 dogs diagnosed with Leishmaniosis. We carried out a slightly modified molecular assay which had been designed by other researchers to detect clonal rearrangements of Immunoglobulin and T cell receptor genes. DNA samples were extracted using commercial kits from K3EDTA bone marrow specimen collected during the diagnostic work-up of dogs with positive serological IFI titers and stored at-20°. For each sample, 4 different PCR reactions were carried out with multiple sets of primers as described in literature. The PCR products were analysed using 6% polyacrylamide gel electrophoresis. One out of 23 samples showed a clonal B cell receptor rearrangement as evidenced by a single, discrete, sharp band without smears or a ladder pattern. This positive subject was referred to our Clinic one year after the onset of clinical signs; the treatment for Leishmaniosis resolved the clinical symptoms and at a 12 month follow-up no clinically detectable lymphoproliferative disorders have been seen. Surprisingly, the dog with persistent IgM monoclonal gammopathy which we reported previously was evaluated and was negative. In the entire cohort, no dog showed clonal rearrangements of TCR, although an evident and intense diffuse band suggesting polyclonality was present in many cases. In conclusion, this study has highlighted the possibility that chronic antigenic stimulation induced by Leishmaniosis may lead to the clonal expansion of lymphoid cells even if only in a small proportion of cases. However, the presence of a clonal subset of lymphoid cells does not imply the presence of an overt lymphoproliferative disorder. As in human patients, where low grade MALT gastric lymphomas associated with H pylori may regress with antibiotic therapy alone, it would also be interesting to ascertain whether the treatment of Leishmaniosis would have led to the disappearance of lymphoid clonality in the case herein described.