Vacuolated plasma cell: ultrastructural distribution of acid phosphatase and intracellular immunoglobulin

In two cases of vacuolated plasma cells, one of which was associated with primary macroglobulinemia and the other was with kappa-chain Bence Jones multiple myeloma, we examined the immunopathological features of the vacuoles in order to know whether the Ig-secreting system or the lysosomal system is of importance in the process of vacuole formation. Immunofluorescent studies detected no Ig in the vacuoles. Detection of intracellular Ig by immunoelectron microscopic technique revealed that Ig was localized only in a small portion of the vacuoles but not in most vacuoles. Even when Ig was included in the vacuoles, only the contents of the vacuoles were positive for Ig but their demarcating membrane was negative for Ig. In contrast, electron microscopic studies of acid phosphatase activity revealed the presence of its activity in all vacuoles. These findings suggest that the lysosomal system but not the Ig-secreting system may play a major role in vacuolation of these myeloma cells.