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Electron microscopic immunocytochemical studies were carried out to localize myelin basic protein and myelin proteolipid protein during the active period of myelination in the developing rat brain using antisera to purified rat brain myelin proteolipid protein and large basic protein. The anti-large basic protein serum was shown by the immunoblot technique to cross-react with all five forms of basic protein present in the myelin of 8-day-old rat brain. Basic protein was localized diffusely in oligodendrocytes and their processes at very early stages in myelination. The immunostaining for basic protein was not specifically associated with any subcellular structures or organelles. The ultrastructural localization of basic protein suggests that it may be involved in fusion of the cytoplasmic faces of the oligodendrocyte processes during compaction of myelin. Immunoreactivity in the oligodendrocyte and myelin due to proteolipid protein appeared at a later stage of myelination than did that due to basic protein. Staining for proteolipid protein in the oligodendrocyte was restricted to the membranes of the rough endoplasmic reticulum, the Golgi apparatus, and apparent Golgi vesicles. The early, uncompacted periaxonal wrappings of oligodendrocyte processes were well stained with antiserum to large basic protein whereas staining for proteolipid protein was visible only after the compaction of myelin sheaths had begun. Our evidence indicates that basic protein and proteolipid protein are processed differently by the oligodendrocytes with regard to their subcellular localization and their time of appearance in the developing myelin sheath.

We report 6 cases of an unusual variant of cutaneous fibrous histiocytoma in which nuclear palisading is a prominent feature. The lesions were equally distributed between males and females with a widely variable age range. Half of the cases occurred on the digits. Histopathologically, the lesions were characterized by areas of nuclear palisading with formation of Verocay-like bodies in addition to the more typical features of the "fibrous" variant of cutaneous fibrous histiocytoma. The differential diagnostic features between these lesions and those of other tumors in which nuclear palisading is seen are discussed.

No abstract

Typical adult cases of malignant lymphoma, diffuse, lymphoblastic type (MLLB), are of the T-cell immunophenotype and occur as mediastinal masses. The authors report two unusual adult cases with initial extranodal sites of involvement and non-T-cell immunophenotype that were originally misclassified. One patient presented with a right submaxillary salivary gland mass and the other presented with a T7-8 spinal cord compression resulting from a vertebral body tumor. A lymphoblastic leukemic phase developed in both patients after 15 months and 5 months, respectively. The bone marrow blasts of both patients had positive results for cluster designation (CD) 10, CD19, HLA-DR, and terminal deoxynucleotidyl transferase. Because both extranodal sites of presentation and non-T-cell immunophenotype are unusual in adult MLLB, these features may have contributed to the original misclassification of these lesions.