Immunohistochemical study of expression of immunoglobulins in canine B-cell lymphomas

Nineteen canine lymphomas were included in this study. Tumors were classified according to the updated Kiel classification adapted for canine lymphomas by Fournel-Fleury et al. Immunoglobulin light chains (kappa and lambda) and IgM and IgG expression were determined by immunohistochemical method. In all examined cases neoplastic cells were positive for one of the immunoglobulin light chains. Expression of lambda light chains and kappa light chains was observed in 18/19 and 1/19 tumors, respectively. In the majority of neoplastic cells in each examined specimen this reaction had a membranous pattern (skappa/slambda). In all examined cases the presence of immunoglobulin light chains was also observed in the cytoplasm of some neoplastic cells (ckappa/clambda). These cells were usally rare and never constituted a dominant population. The expression of immunoglobulin was found in 13/19 cases. Most lymphomas were sIgM positive (11/13 cases). In one case expression of IgG was found, and in another lymphoma two populations of neoplastic cells with different expression of examined immunoglobulins (cells with IgM+ and IgG+ phenotypes) were observed. The reaction also had a membranous pattern. The cells containing cytoplasmic immunoglobulins were rare, and in most cases were of the same type as the surface immunoglobulins. Our study has confirmed that canine lymphomas are a monoclonal proliferation of B-cells usually expressing immunoglobulin lambda light chains and that the vast majority of tumors deriving from B-cells express IgM. Our study also indicates a possibility of occurence of biclonal lymphomas in canine species.