Stages of development of the ribosome-lamella complex: an ultrastructural study.

Ribosome-lamella complexes (RLC) are intracytoplasmic organelles observed in a wide variety of disorders, but mostly in hematologic malignancies. Although their close topographic relationship with rough endoplasmic reticulum (RER) suggests their derivation from it, their development and functional role are unclear. Their maturation phases were studied in 20 cases (19 hematologic neoplasms and 1 parathyroid adenoma) where electron microscopy had evidenced their presence. In 19 of thesecases, RLC were in an advanced stage of maturation, whereas in one (acute monoblastic leukemia) they were observed in the early stages of development and appeared to arise from peculiar RER configurations within blast cells, which were rich in both organelles. In this case, the authors observed numerous RER cisternae with distinctive cylindric, concentric and/or whorl configurations, RLC associated and not associated with these configurations, and intermediate structures. The latter were characterized by lamellae devoid of ribosomes oriented parallel to the RER configurations. Reticulum configurations were observed in no other case. The ultrastructural aspects observed in these 20 cases suggest that RLC synthesis proceeds as follows: (1) arrangement of RER in cylindric configurations; (2) synthesis of lamellae oriented parallel to the cylindric configurations (pre-RLC); (3) formation of RLC when ribosomes appear between the lamellae associated with configurations (immature RLC); (4) formation of mature RLC with disappearance of the reticulum.