[Electronmicroscopic and immunohistochemical studies on human lymphocytes]

Mitochondrial regulation of store-operated calcium signaling in T lymphocytes

Mitochondria act as potent buffers of intracellular Ca2+ in many cells, but a more active role in modulating the generation of Ca2+ signals is not well established. We have investigated the ability of mitochondria to modulate store-operated or "capacitative" Ca2+ entry in Jurkat leukemic T cells and human T lymphocytes using fluorescence imaging techniques. Depletion of the ER Ca2+ store with thapsigargin (TG) activates Ca2+ release-activated Ca2+ (CRAC) channels in T cells, and the ensuing influx of Ca2+ loads a TG-insensitive intracellular store that by several criteria appears to be mitochondria. Loading of this store is prevented by carbonyl cyanide m-chlorophenylhydrazone or by antimycin A1 + oligomycin, agents that are known to inhibit mitochondrial Ca2+ import by dissipating the mitochondrial membrane potential. Conversely, intracellular Na+ depletion, which inhibits Na+-dependent Ca2+ export from mitochondria, enhances store loading. In addition, we find that rhod-2 labels mitochondria in T cells, and it reports changes in Ca2+ levels that are consistent with its localization in the TG-insensitive store. Ca2+ uptake by the mitochondrial store is sensitive (threshold is <400 nM cytosolic Ca2+), rapid (detectable within 8 s), and does not readily saturate. The rate of mitochondrial Ca2+ uptake is sensitive to extracellular [Ca2+], indicating that mitochondria sense Ca2+ gradients near CRAC channels. Remarkably, mitochondrial uncouplers or Na+ depletion prevent the ability of T cells to maintain a high rate of capacitative Ca2+ entry over prolonged periods of >10 min. Under these conditions, the rate of Ca2+ influx in single cells undergoes abrupt transitions from a high influx to a low influx state. These results demonstrate that mitochondria not only buffer the Ca2+ that enters T cells via store-operated Ca2+ channels, but also play an active role in modulating the rate of capacitative Ca2+ entry.

Stereologic analysis of the ultrastructure of isolated human T and non-T lymphoid cells. III. Studies in chronic lymphoid leukemias, hairy cell leukemia and some malignant lymphomas

Malignant cells from 9 cases of chronic lymphocytic leukemia (CLL), 4 cases of prolymphocytic leukemia (PLL), 4 cases of hairy cell leukemia (HCL), 4 cases of malignant lymphoma of centrocytic type and 3 cases of malignant lymphoma of lymphoblastic type (Kiel classification), all examined for T and B markers, were analysed by electron microscopy. Stereological methods were applied to assess relative and absolute values concerning the whole cell and nuclear and cytoplasmic components of the average cell in each population, and comparisons were made between the morphologically and immunologically defined subsets. The CLL-lymphocyte possessed the smallest cell volume, a high nucleo-cytoplasmic volume ratio, densely packed heterochromatin, a small nucleolar volume and a sparse Golgi complex. The 7 B-derived cases were characterized by a larger volume of rough ER and a more irregular plasma membrane than the two T-derived cases, which typically displayed dense granules in paranuclear aggregations. The prolymphocyte could be distinguished from the CLL-cell by its larger cell volume, lower nucleo-cytoplasmic volume ratio, proportionally lesser heterochromatin, typically condensed at the periphery and around a prominent nucleolus. All 4 cases of PLL were of B-nature and shared the features of B-CLL regarding increased rough ER and low content of granules. The hairy cell exhibited the largest cell volume, the lowest nucleo-cytoplasmic volume ratio, an indented nucleus and a remarkable irregular cellular surface with long "hairy" processes. The cytoplasmic inclusions of ribosome-lamella complexes were recorded exclusively in hairy cells, in half of the patients. The centrocyte was characterized by a cell volume of intermediate size, a high nucleo-cytoplasmic volume ratio and the highest degree of nuclear irregularity recorded. The amount of rough ER was considerably less than in B-CLL and B-PLL. Finally, the blast from the cases of lymphoblastic lymphoma, all of T-nature, displayed a smooth plasma membrane, a high euchromatin-heterochromatin volume ratio and dense granules, characteristically clustered in the vicinity of the Golgi complex. Stereology on the ultrastructure of malignant lymphoid cells provides a more accurate characterization and may be helpful in classification.

[T-cell leukemias of adulthood]

9 adult patients suffering from different forms of T-cell-malignancies were investigated: 4 patients with T-ALL; 1-T-ALL-CLL mixed form (prolymphocytic); 2 T-CLL; 2 Sézary-syndrome. The clinical peculiarities of the different forms of leukemias were compared: involvement of lymph nodes and spleen, of the central nervous system and the skin was frequent; in contrast to the findings in Sézary-syndrome, bone marrow infiltration was prominent. Light and electron microscopic morphology of the malignant cells are described. In all cases a strong activity of acid phosphatase was demonstrated, in one patient prominent deposits of glycogen. The T-cell-quality of the respective malignant cell population as well as the B-T-cell distribution of the remaining "normal" lymphocytes were shown by the following cell markers: demonstration of T-cell-antigen, resp. membrane immunoglobulins with the aid of specific heterologous antisera conjugated with peroxidase, 125iodine or fluoresceine; complement consumtion or cytotoxicity with such antisera; spontaneous rosette formation with sheep red cells or with acrylic acid beads. Usually, there was a good coincidence in results obtained with the different markers. In two patients, however, T-cells demonstrated by anti-T-globulin were not able to form T-rosettes. Responsiveness of the malignant T-cells and also of the remaining "normal" blood lymphocytes to different mitogens usually was depressed, immunoglobulin levels in the blood mostly were normal. Taking all findings into consideration, T-cell-leukemias of the adult represent a special group of hematological malignancies; the different subgroups show similarities; transitional forms occur.