Immunoglobulin light chain restriction and clonal rearrangement in nodular paragranuloma

B-cell clonality was demonstrated in a typical nodular paragranuloma case (NP) by both immunoglobulin (Ig) surface analysis and Ig genes rearrangement studies. On frozen sections, immunostaining for Ig light chain expression revealed a clear-cut predominance of Ig lambda-expressing cells, recognizable as both small lymphocytes and lympho-histiocytic (L&H) cells. Accordingly, molecular analysis of the Ig genes showed a monoclonal rearrangement of the lambda chain gene, although no specific pattern of heavy chain gene rearrangement could be detected by JH analysis. The C lambda rearranged band was identified with two different restriction enzymes, excluding the hypothesis of a genomic polymorphism. Furthermore, the C kappa gene was almost completely deleted, indicating that the developmental hierarchy of Ig genes rearrangement has been respected. The molecular pattern of the C lambda hybridizing band was consistent with monoallelic rearrangement of almost the entire DNA sample, indicating that clonal proliferation was not limited to L&H cells, but also involved surrounding lymphocytes. This finding is in keeping with the immunohistochemical evidence of a lambda light chain restriction on both L&H cells and small lymphocytes, pointing to a close relationship between these two cell types. Our results as a whole suggest that L&H cells and B lymphocytes share a common origin and may both be involved in clonal proliferation in NP.