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Cell biology has been divided into 19 topics for the purpose of planning audiovisual materials. One of these topics, the structure and function of cell membranes, has been developed as a series of seven self-instructional slide-tape units and tested in five medical schools. Organization of advisers, analysis and definition of objectives and content, and development and evaluation of scripts and storyboards are discussed.
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Programmed cell death protein 1 (PD-1, CD279) is a pivotal inhibitory immune checkpoint receptor that plays a central role in maintaining immune homeostasis and peripheral tolerance. Originally characterized as a negative regulator of T-cell activation, PD-1 limits excessive immune responses and prevents autoimmunity, while its sustained expression under conditions of chronic antigen stimulation contributes to T-cell dysfunction and exhaustion. The discovery that blockade of the PD-1 pathway can restore anti-tumor immunity has revolutionized cancer therapy and established immune checkpoint inhibition as a cornerstone of modern oncology. Although PD-1 has traditionally been viewed as a key regulator of adaptive immunity, accumulating evidence indicates that its biological functions extend beyond T cells. In recent years, PD-1 expression has been identified in several innate immune cell populations, particularly Natural Killer (NK) cells, where it has emerged as an important modulator of effector functions, cytokine production, metabolic fitness, and antitumor activity. These findings have challenged the classical view of PD-1 biology and revealed unexpected similarities between NK-cell dysfunction and the exhausted phenotype described in chronically stimulated T cells. In the tumor microenvironment, PD-1 expression on NK cells has been associated with impaired cytotoxicity and reduced immune surveillance, suggesting that NK cells may also represent relevant targets of PD-1-mediated immunosuppression. At the same time, the mechanisms regulating PD-1 expression and signaling in NK cells appear to differ, at least in part, from those operating in T lymphocytes, highlighting the complexity of this pathway across distinct immune cell subsets. In this review, we summarize the current knowledge of PD-1 biology, from its established role in T-cell regulation to its emerging functions in NK cells. We discuss the molecular mechanisms governing PD-1 expression and signaling, its contribution to immune dysfunction in cancer and chronic diseases, and the potential implications of targeting the PD-1 axis to enhance both adaptive and innate antitumor immunity.
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The light scattered from nucleated biological cells has been investigated by using four different theoretical models: an opaque disk, a homogeneous sphere, an opaque ring, and a coated sphere. By comparing these four models, diffraction at the edges of the cell and the nucleus has been found to be the predominate scattering mechanism for nucleated biological cells at low angles. The scattering patterns of nucleated cells are found to have a fine lobe (high-frequency) structure dependent on whole cell size, and an envelope lobe (low-frequency) structure dependent on relative nucleus size. The models indicate that the present technique for measuring cell size with a single low-angle light detector is highly dependent on the nucleus to cell diameter ratio. Whole cell size is better estimated by the ratio of the outputs from two low-angle detectors.
Some aspects of the cell biology of normal and leukaemic haematopoietic cells are reviewed. Important points are: (a) normal and possibly also leukaemic stem cells differ from more mature cells in the kinetics as well as in cell surface antigens and other properties; (b) leukaemic cells are subject to a population size control as are normal haematopoietic cells; (c) part of the normal control seems to be chalone feedback regulation of proliferation and maturation rate of precursor cells; (d) evidence is accumulating that C-type oncornaviruses may cause leukaemia in man. Various experimental and established forms of therapy for leukaemia are discussed: No alterative exists to chemotherapy in acute lymphoid leukaemia. Granulocyte chalone may possibly become a valuable adjunct to other types of therapy in acute myeloid leukaemia. Immunotherapy may prove as efficient as maintenance chemotherapy in this disease. So far it has not been possible to synchronize leukaemic and normal cells so as to occupy different positions in the cell cycle. Nor has a forced maturation of human leukaemic cells been effected. Neither bone marrow transplantation nor prophylaxis by vaccination are considered worthwhile procedures for the time being. Anti-viral therapy has been promising in animal experiments, but animal leukaemias are often poor models for the disease in man. Assessment of treatment, using stem cell assays, is advocated.
In this review I have attempted to explain the processes of chemotaxis, phagocytosis, oxidant generation, and lysosomal degranulation in normal and genetically abnormal human PMN. In my view these leukocyte functions are most importantly dependent on the integrity of three cellular components: the plasma membrane, the submembranous microfilaments, and the cytoplasmic microtubules. These components are often discussed in isolation, and the biochemical and pharmacological aspects of their function are analyzed separately here. However, PMN motile and bactericidal activities require the interdependent functioning of membranes, microtubules, and microfilaments. I have therefore tried to provide an integrated view of cytoskeleton-membrane organization and function in human PMN. I have particularly emphasized dynamic aspects of the cytoskeleton and membranes, eg, the induction of microtubule assembly and membrane enzyme activation by surface ligands and the reorganization of microfilaments in response to the same ligands. With this background established, I have selected for discussion a series of diseases in which abnormalities of chemotaxis, phagocytosis, lysosomal degranulation, and/or oxidant generation can be explained directly or indirectly by abnormalities in dynamic properties of PMN membranes, microtubules, or microfilaments. I emphasize that even preliminary insight into the basis of these disorders has sometimes been sufficient to suggest useful clinical approaches to the management of patients. In several of these neutrophil abnormalities, ie, neutrophil actin dysfunction, Chédiak-Higashi syndrome, and its "antithesis" described by Gallin and co-workers, the cellular dysfunctions were well documented but the molecular basis was completely obscure prior to cell biologic analysis. Snyderman and Pike 159 and Chusid and co-workers 160 emphasized the existence of a large number of other neutrophil bactericidal abnormalities resulting from as yet unexplained cellular defects. Further analyses of the functional interactions between membranes and cytoskeletal components in neutrophils may not only clarify the molecular bases of the disorders described here but also may provide insight into the origins and proper therapeutic approach to other granulocyte dysfunctions.
A system for scanning biological cells under high magnification has been developed which utilizes a three-color photometer. The spectral information has proved useful in improving computer recognition of certain cell types.
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Human lymphoid cell lines were studied as an experimental model for the spontaneous or induced occurrence of tuburloreticular structures (TRS). It was possible to induce TRS after culturing the EB-3 cell line with 20 mug/ml bromodeoxyuridine (BrUdR) during 96 h. Starvation, culturing at lower temperature (32 degrees) or inhibition of DNA synthesis did not give rise to the production of TRS. The response to BrUdR could be blocked with 60 mug/ml thymidine but not with 60 mug/ml deoxycytidine. The addition of 5 mug/ml cytarabine or the removal of BrUdR at different times resulted in inhibition of TRS induction, indicating that BrUdR had to be incorporated into DNA during at least 48 h. After incorporation, neither the presence of BrUdR nor DNA synthesis was necessary for the production of TRS. These experiments and the finding that in the cell line IHTC-33, which does not produce Epstein-Barr virus associated antigens, TRS were spontaneously present, exclude a correlation between TRS and these antigens. However, the induction of TRS by BrUdR may be related to the activation of another (latent) virus.
On the basis of elastic waves released by imploding cavitation bubbles, a mechanism for biological cell disintegration in high intensity ultrasound has been proposed. Comparison of this mechanism with the published results on yeast cells shows many points of agreement suggesting that yeast cell disintegration in ultrasonic cavitation occurs by shear stresses developed by viscous dissipative eddies arising from shock waves.
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The anomalous diffraction approximation has been used in an attempt to account for the low-angle scattering from composite spheres. These are used as models for biological cells. Solutions have been obtained for both thinly and thickly coated spheres.
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