IMMUNOGLOBULIN LIGHT-CHAIN RESTRICTION AND CLONAL REARRANGEMENT IN NODULAR PARAGRANULOMA

B-cell clonality was demonstrated in a typical nodular paragranuloma c ase (NP) by both immunoglobulin (Ig) surface analysis and Ig genes rea rrangement studies. On frozen sections, immunostaining for Ig light ch ain expression revealed a clear-cut predominance of Igh-expressing cel ls, recognizable as both small lymphocytes and lympho-histiocytic (L&H ) cells. Accordingly, molecular analysis of the Ig genes showed a mono clonal rearrangement of the A chain gene, although no specific pattern of heavy chain gene rearrangement could be detected by JH analysis. T he Ch rearranged band was identified with two different restriction en zymes, excluding the hypothesis of a genomic polymorphism. Furthermore , the CK gene was almost completely deleted, indicating that the devel opmental hierarchy of Ig genes rearrangement has been respected. The m olecular pattern of the Ch hybridizing band was consistent with monoal lelic rearrangement of almost the entire DNA sample, indicating that c lonal proliferation was not limited to L&H cells, but also involved su rrounding lymphocytes. This finding is in keeping with the immunohisto chemical evidence of a h 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 lymph ocytes share a common origin and may both be involved in clonal prolif eration in NP.