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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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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.
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Cultured normal human and animal cells are predestinued to undergo irreversible functional decrements that mimick age changes in the whole organism. When normal human embryonic fibroblasts are cultured in vitro, 50 +/- 10 population doublings occur. This maximum potential is diminished in cells derived from older donors and appears to be inversely proportional to their age. The 50 population doubling limit can account for all cells produced during a lifetime. The limitation on doubling potential of cultured normal cells is also expressed in vivo when serial transplants are made. There may be a direct correlation between the mean maximum life spans of several species and the population doubling potential of their cultured cells. A plethora of functional decrements occur in cultured normal cells as they approach their maximum division capability. Many of these decrements are similar to those occurring in intact animals as they age. We have concluded that these functional decrements expressed in vitro, rather than cessation of cell division, are the essential contributors to age changes in intact animals. Thus, the study of events leading to functional losses in cultured normal cells may provide useful insights into the biology of aging.
Radiation therapy is used as total body treatment in preparation of the acute myelogenous leukemia (AML) patient for bone marrow transplantation. Many AML patients will have residual leukemia cells at the time of total body irradiation (TBI). In the present study, the effect of TBI on leukemic myeloid cells was compared to the effect on normal marrow granulocytic stem cells (CFUc) in vitro. Little difference from that of normal CFUc was found in the radiosensitivity of two mouse myeloid leukemia cell lines. The effect of TBI on growth of WEHI-3 or J774 cells in millipore diffusion chambers was stimulatory. These AML cell lines as well as others derived from Friend or Abelson virus infected in vitro long term mouse marrow cultures showed some morphologic differentiation by 7 days growth in diffusion chambers in irradiated heterologous rat hosts, but immature cells predominated by day 21. Thus, evidence in murine models of AML indicates that residual AML cells surviving chemotherapy will show no greater susceptibility to radiation killing compared to normal stem cells and will rapidly repopulate the irradiated host.