To investigate the mechanisms underlying the development of extranodal MALT-type lymphomas, the immunoglobulin receptor was sequenced and analyzed for antigen specificity using heterohybridoma technology.Furthermore, CD40 ligand expression was evaluated by immunohistochemistry and by semiquantitative RT-PCR,and ligand binding to the CD40 of tumor B cells was studied using the CD40 system. The gene discussed is CD40LG; the disease is neoplasm.