Signet-ring cell lymphoma. Ultrastructural and immunohistochemical features of three varieties.

An ultrastructural and immunohistochemical study was performed on three malignant lymphomas of follicular center cell origin with signet-ring cells. The first case corresponded to a diffuse lymphoma with follicular center cells and plasmacytic features; the other two cases corresponded to the nodular centrocytic-centroblastic category. The neoplastic lymphocytes contained Russell bodylike inclusions, clear vacuoles, and ill-defined eosinophilic masses, respectively, which produced a displacement of the nuclei to the periphery. Ultrastructurally, there were three different morphologic types because of the following cytoplasmic changes: the accumulation of electron-dense granular material in the cisternae of the rough endoplasmic reticulum; the formation of clear vacuoles with a smooth limiting membrane; and, the presence of granular-fibrillar and crystalline material in the hyaloplasm without a limiting membrane. The first type of signet-ring cell contained monoclonal immunoglobulin (IgM-K). No immunoglobulins were found in the clear cytoplasmic vacuoles of the second type; however, the rim of cytoplasm stained for IgG, kappa and lambda. Finally, the third type showed IgG and kappa light chain in the hyaloplasmic inclusions. It is concluded that the signet-ring cell appearance is due to an abnormal production and secretion of immunoglobulins.