Preparing the lethal hit: interplay between exo- and endocytic pathways in cytotoxic T lymphocytes

Cytotoxic T lymphocytes patrol our body in search for infected cells which they kill through the release of cytotoxic substances contained in cytotoxic granules. The fusion of cytotoxic granules occurs at a specially formed contact site, the immunological synapse, and is tightly controlled to ensure specificity. In this review, we discuss the contribution of two intracellular compartments, endosomes and cytotoxic granules, to the formation, function and disassembly of the immunological synapse. We highlight a recently proposed sequential process of fusion events at the IS upon target cell recognition. First, recycling endosomes fuse with the plasma membrane to deliver cargo required for the docking of cytotoxic granules. Second, cytotoxic granules arrive and fuse upon docking in a SNARE-dependent manner. Following fusion, membrane components of the cytotoxic granule are retrieved through endocytosis to ensure the fast, efficient serial killing of target cells that is characteristic of cytotoxic T lymphocytes.     

Peroxidase activity of neutrophil granules in two cases of congenital myeloperoxidase deficiency]

The neutrophils and monocytes of two patients with hereditary myeloperoxidase deficiency lacked myeloperoxidase activity as determined by light and electron microscopic cytochemical staining. Using Graham-Karnovsky media, azurophils of neutrophils were devoid of peroxidase whereas all eosinophilic and basophilic granules exhibited normal peroxidase activity. After incubation in alkaline diaminobenzidine media which stains the catalase of microperoxisomes, some small granules were seen to be strongly stained in both immature and mature neutrophils. These small granules were distinct from all other neutrophilic granules which lacked a positive reaction. Only, in the presence of cyanide or aminotriazole, peroxidatic activity was also detected in some ellipsoid azurophils. This observation suggests that these substances activated an oxidase whose nature is discussed.     

Reinterpretation of the ultrastructure of cartilage matrix.

The epiphyseal cartilage from new-born mouse was treated with collagenase in two ways: either before fixation or after glutaraldehyde fixation. The electron dense granules of the matrix were not seen in the micrographs of cartilage treated with collagenase before fixation. It is concluded that collagen plays a definite role in the formation of the granules at the time of tissue fixation and that the granules are fixation artifacts.     

Modifications ultrastructurelles provoquées par quelques médicaments sur les terminaisons nerveuses adrénergiques et sur la médullaire surrénale

Summary It has been shown that reserpine and guanethidine deplete granules containing catecholamine in sympathetic nerve endings of both the pineal gland and the vas deferens. This effect is blocked by iproniazid. Bretylium is not able to deplete these granules but it modifies their aspect. It has also been observed that granules of the adrenal medulla are depleted less easily than those of sympathetic nerve endings.     

Quantitative ultrastructural features of maturing mononuclear phagocytes in rat peritoneal fluids.

Ultrastructural features of the in vivo transformation of macrophage congeners in resident and adjuvant-induced peritoneal populations are evaluated by sterological methods. Maturation involves an increase in cell size by the differential hypertrophy of subcellular compartments, notably remaining cytoplasm, nucleus and lysosome-like granules. Larger cells have more and larger granules, more mitochondria and a greater plasmalemmal surface. In contrast, adjuvant activation tends to produce fewer granules and a nett loss of surface membrane.     

Reinterpretation of the ultrastructure of cartilage matrix

Summary The epiphyseal cartilage from new-born mouse was treated with collagenase in two ways: either before fixation or after glutaraldehyde fixation. The electron dense granules of the matrix were not seen in the micrographs of cartilage treated with collagenase before fixation. It is concluded that collagen plays a definite role in the formation of the granules at the time of tissue fixation and that the granules are fixation artifacts.Commonwealth Academic Staff Fellow. Permanent address: Department of Zoology, University of Poona, Poona 411007, India.     

Pigment granules in choroidal melanophores of the albino goldfish.

Pigment granules in choroidal melanophores of the albino goldfish contained fine particulate materials which were in various degrees aggregated in clumps. Tyrosinase was considered to be present in an inhibited state in these pigment granules.     

Genesis of concentric laminated inclusions in the nucleus

Summary Single-membrane-bound inclusions containing zymogen granules were found in pancreatic acinar cells. Images were seen suggesting that the concentric laminated inclusion is derived by hydration and fusion of such granules within the inclusion.     

Genesis of concentric laminated inclusions in the nucleus

Single-membrane-bound inclusions containing zymogen granules were found in pancreatic acinar cells. Images were seen suggesting that the concentric laminated inclusion is derived by hydration and fusion of such granules within the inclusion.     

Intracellular localization of calcitonin in the C cells of the rat.

Specific localization of C cells at the electron microscope level was achieved by an indirect immunoperoxidase technique. The hormone is present in the electron dense granules. The presence of granules apparently devoid of calcitonin was also detected.     

Platelet heterogeneity and dense tubular system changes on activation

Platelets impregnated with heavy metals appeared as 3 distinct morphological types: 'reticular' cells with a polygonal dense tubular network and stained granules, dark metallophilic cells, and pale metallophobic cells with microvesicles and non-staining granules. On stimulation, type 1 cells decreased while type 3 cells increased, suggesting that with activation dense tubules break up into microvesicles and granules become metallophobic. In the type 2 cells a different functional mechanism may exist.     

Ultrastructure of neurosecretory granules in the sinus gland of Palaemon serratus Pennant]

Five types secretory granules are distinguished in the sinus gland of Palaemon serratus on the basis of differences in their diameter and their electron density. Variations in the density of the acoplasm and of the granules are observed for three of these granule types.     

Intracellular localization of calcitonin in the C cells of the rat

Summary Specific localization of C cells at the electron microscope level was achieved by an indirect immunoperoxidase technique. The hormone is present in the electron dense granules. The presence of granules apparently devoid of calcitonin was also detected.We thank Miss Nicole Mendoza for her technical collaboration.     

Preliminary observations on the co-existence of regulatory peptides in cells of the baboon endocrine pancreas

Summary Immunocytochemical procedures at ultrastructural and light microscopy level revealed, in the Chacma baboon endocrine pancreas, cells which were immunoreactive for glucagon and pancreatic polypeptide (PP). Some D cells were observed to contain secretory granules with both the appearance and immunoreactivity of A cell secretory granules.     

Preliminary observations on the co-existence of regulatory peptides in cells of the baboon endocrine pancreas

Immunocytochemical procedures at ultrastructural and light microscopy level revealed, in the Chacma baboon endocrine pancreas, cells which were immunoreactive for glucagon and pancreatic polypeptide (PP). Some D cells were observed to contain secretory granules with both the appearance and immunoreactivity of A cell secretory granules.     

Daily variations of the level of neural secretions in Owenia fusiformis. Persistance of a daily rhythm in cultured tissues]

A quantitative study of elementary granules in neuron axons of the nervous chain of Owenia fusiformis (Annelid polychaete) shows that daily variations of the number of secretory granules occur in unamputated animals and in ventral tissue cultures.These variations are correlated with the thythm of the cell cycle.     

Elektronenmikroskopischer Nachweis spezifischer Grana in den Sympathicoblasten der Grenzstrangganglien von Hühnerembryonen

Summary With regard to the cytodifferentiation of neurones in the developing CNS and the spinal ganglia, only the sympathoblasts of the primary and secondary sympathic trunk of chick embryos contain a varying amount of catechol amine-containing granules. The formation of these granules takes place in rather early stages of development.     

Beobachtungen über das Auftreten von Keratohyalingranula im Zellkern

Summary Electron microscopic studies on the oesophageal epithelium of the rat revealed for the first time intranuclear granules of keratohyalin. The results strongly suggest that these granules were extruded from the nucleus and were enlarged in the cytoplasm by ribonucleoprotein (RNP) particles aggregating to the keratohyalin.     

Unusual membrane fracture faces in polymorphonuclear leukocyte granules

Summary Freeze fracturing of azurophil and specific granules from rabbit polymorphonuclear leukocytes reveals unusually high numbers of intramembrane particles. Both granules have significantly higher particle densities on the B than on the A fracture face.This work was supported in part by grant No. 3.553.75 from the Swiss National Science Foundation.     

Relationship between lectin-affinity granules in anuran embryos and formation of primordial germ cells

Embryos of the anuran, Rana nigromaculata, contained granules with a specific affinity for Con A and GS-I. Larvae derived from embryos injected with these lectins had a noticeable reduction in both the number and size of primordial germ cells (PGCs). This observation suggests that the granules are somehow involved in the formation of PGCs.