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Methods to Assess Beta Cell Death Mediated by Cytotoxic T Lymphocytes
Published on: June 16, 2011
Ultrastructure of cell mediated cytotoxicity
1University of Zürich-Irchel, Institute of Anatomy, Switzerland.
Insights
Cell-mediated cytotoxicity involves various immune cells like lymphocytes and macrophages. Morphological studies reveal distinct features of cytotoxic effector cells, but their functional pathways remain unclear.
Area of Science:
- Immunology
- Cell Biology
- Cytotoxicity
Background:
- Contact-dependent cell-mediated cytotoxicity is executed by lymphocytes, macrophages, and granulocytes.
- Lymphatic cytotoxic effector cells include cytotoxic T lymphocytes (CTL) and non-MHC restricted effectors like natural killer (NK) cells, T lymphocytes with NK-like activity, and lymphokine-activated killer (LAK) cells.
- These cells share morphological features of large granular lymphocytes (LGLs) with specific ultrastructural granule characteristics and unique cellular specializations.
Purpose of the Study:
- To investigate the morphological characteristics of cytotoxic effector cells involved in cell-mediated cytotoxicity.
- To examine the ultrastructural features of granules within these cytotoxic cells.
- To differentiate between morphologically distinct modes of target cell killing.
Main Methods:
- Morphological analysis of cytotoxic effector cells, including lymphocytes, macrophages, and granulocytes.
- Ultrastructural examination of lysosomal granules, identifying components like perforin, serine esterases, and proteoglycans.
- Distinguishing between two types of cell killing based on target cell membrane and nuclear changes.
Main Results:
- Cytotoxic effector cells exhibit features of large granular lymphocytes (LGLs) with characteristic granules containing cytotoxic proteins.
- Specific ultrastructural features such as parallel tubular arrays (PTA) in NK cells and nuclear inclusion bodies in LAK cells were observed.
- Two distinct morphological patterns of target cell destruction were identified: one involving membrane lesions and the other resembling apoptosis.
Conclusions:
- While cytotoxic effector cells share common morphological traits, specialized structures exist within different cell types.
- Distinct morphological outcomes of target cell destruction were observed.
- Further research is needed to determine if these distinct morphological killing events correlate with functionally different pathways of cell-mediated cytotoxicity.
Abstract:
Contact dependent cell mediated cytotoxicity has been found to be executed by lymphocytes, macrophages, and even granulocytes. Cytotoxic effector cells of the lymphatic lineage are divided into cytotoxic T lymphocytes (CTL), mediating MHC related cytotoxicity, and in effectors mediating non-MHC restricted cytotoxicity such as natural killer (NK) cells, T lymphocytes displaying NK-like activity and lymphokine activated killer (LAK) cells. In morphologic studies these cells are hardly to be distinguished: they all show features of large granular lymphocytes (LGLs), which are characterized by a low nuclear to cytoplasmic ratio and azurophilic granules. Ultrastructurally lysosomal granules, showing an electron dense core that is either surrounded by numerous small vesicles or by a small electron translucent halo, have been found. Pore-forming proteins such as perforin, as well as serine esterases and proteoglycans have been pointed out in these granules. Specialties are parallel tubular arrays (PTA) in NK cells and nuclear inclusion bodies in LAK cells. Morphologically two types of killing event may be distinguished. In one way membrane lesions develop at the surface of target cells upon binding of effector cells and in advanced stages of cytolysis the target cells are surrounded by a completely disintegrated membrane. The nuclei, however, show only minor changes. In the other way, called apoptosis, the cell membrane of the targets remains intact, but the nucleus and cell organelles very early disintegrate intracellularly. Whether these morphologically different types of cell killing correspond to the functionally different pathways of cell mediated cytotoxicity remains to be resolved.
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