Postepy Biologii Komorki, vol. 32, 2005, issue 1

Immunological Synapsesand their Role in Effector Mechanisms of the Immune System

Summary: T cells and antigen presenting cells (APC) form a specialized cell-cell junction termed the immunological synapse (IS). It is characterized by a central region of antigen receptors, a ring of integrin family adhesion molecules, and temporal stability over hours. This minireview discusses the current knowledge on the formation, function and diversity of immunological synapses. Cytoskeletal remodeling in T cells, which is connected with signals delivered by costimulatory molecules, plays a crucial role in a formation of IS. Microclusters (MCs) are the site for initial and sustained T cell receptor (TCR) signals. T lymphocytes form different ISs depending on their state of activation, on APCs with which they interact, also on environmental conditions and antigen load. The types of interactions between T cells and APC range from stable and long lived to dynamic and short lived. Although biological role of the IS has not been fully characterized we know well that this process is crucial for the antigen recognition particularly in the adaptive immune response of T cells.

Key words: immunological synapse (IS), T lymphocytes, antigen presenting cells (APC), cytoskeleton, costimulation

Summary: Abstract: Root border cells (RBC) formerly called dead sloughed root cap cells are live cells released to soil by the growing root from the outermost cap layer. They differ from root tip cells in morphology, pattern of synthesized proteins and function. The number of RBC produced by a given root during a 24-h period is conserved at the family level. Production and RBC release from the root cap is controlled by endo-genous signals and many environmental factors. Metabolites synthesized by RBC released from the root cap and exported from cells include polysaccharides which facilitate penetration of the soil by the cap, proteins (enzymes and biocides), factors controlling plant and microbial cell division, and attractants for bacteria, fungi and nematodes. The above-mentioned properties of RBC indicate that they are a significant factor affecting the composition and structure of the rhizospheric microbial community and also are involved directly or indirectly in interaction between plants and soil microorganisms.

Key words: root border cells (RBC), morphology, metabolites, function in root zone

Summary: The cell system that detoxificates organic xenobiotics comprises three stages. Each of them involves a number of enzymes that, depending on the character of the degraded organic compound, lead to its transformations. The enzymes of the first stage – bioactivation – are generally polysubstrate monooxygenases, flavine-containing monooxygenases (FMO), and the enzymes showing hydrolytic and oxidoreductive activity. Induction of the enzymes influenced by xenobiotic has been confirmed by the SAGE studies (Serial Analysis of Gene Expression). The products of the first stage become the substrates of the second stage, that is the stage of conjugation with endogenous substrate. Couplings with glucose catalyze the UDP-dependent transferases with the aminoacid-N-acetyl transferase (ACT), while those with glutathione – the most diversified divided into 5 classes and consisting of 20 isoenzymatic forms – the glutathione transferase family (GST). The transport of the resulting conjugates through tonoplast is led by the Mg group and ATP-dependent transporters (ATP-binding Casette). The xenobiotics accumulated in a vacuole are further modified under the influence of peroxidases and carboxypeptidases. Except for the enzymes involved in the three stages of detoxification of organic compounds, there is an enzymatic system for cell antioxidative protection, conditioning the level of plant tolerance to stress caused by organic contamination, which is also very important in the degradation process.

Key words: detoxification, organic pollutants, phytoremediation

Summary: Cell death is a genetically regulated process occurring commonly in nature. For decades cell death was considered to be typical only for multicellular organisms and, consequently, relatively young in evolutionary terms. However, genetically regulated cell death has recently been documented in many unicellular organisms, both eukaryotic and prokaryotic. These data suggest that cell death might be an old process accompanying life since its beginning. In this paper, examples of cell death processes in different organisms are compared. On that basis an overview of hypotheses on origin and evolution of cell death is presented. Possible ways for the emergence of different cell death mechanisms are also discussed.

Key words: cell death (origin), Eukaryotes, evolution, multicellular organisms, Prokaryotes, unicellular organisms

Dendritic Cells as Regulators of Immune Response and their Application in Therapy

Summary: Dendritic cells are one of the major populations of immune cells. Due to the presence of specific receptors dendritic cells (DCs) are able to respond to both intra- and extracellular antigens. The diversity of this cell population is a result of differences in localization, stage of maturation, phenotype and function. In recent years there has been a shift in perception of DCs not only as inducers of immune reactivity but also as crucial regulators of immunity, which include ability to induce and maintain tolerance and also as effector cells, which are capable to kill tumor cells (NKDCs). Scientists around the world are analyzing the role of DCs in generation, maintenance or inhibition of pathological conditions, such as: tumors, autoimmune diseases or graft rejection. Highly developed research are focused on generating and modulating the activity as well as genetic modifications of DCs. All knowledge obtained in those research may contribute to the acceleration of DC-based therapies in clinics. Mimicking natural properties of pathogen structural elements (i.e. bacterial cell wall), that induce immune response, scientists try to design safer and more effective analogs (MDP, MB, CpG-ODN) to use them to improve health condition in patients with defective immune system reactivity.

Key words: dendritic cells, immunomodulators, muramylopeptides, Toll-like receptors, CpG

The Role of Non-Enzymatic Glycosylation of Proteins in Ageing Processes and Pathogenesis of Geriatric Diseases

Summary: Ageing and diseases connected with ageing currently became very important social problem. Ageing processes can be faster because of accumulation of toxic metabolic products. This substances could be products of non enzymatic glycosylation (glycation). Glycation may there fore play an important role in ageing and has been implicated in the pathophysiology of a number of diseases, like: Alzheimer disease, arteriosclerosis, diabetes, kidney diseases, blood circulation system diseases and lung diseases. Products of non-enzymatic glycosylation of proteins are formed in chemical reaction between reducing sugar, frequently glucose molecule and free amino groups located either at the N-terminal end of the polypeptide chains or on the lysine side chains. They are long-living molecules which can form cross-linking between proteins and extracellular matrix.

Summary: Changes of sugar concentration often affect germination, plant growth, metabolic processes and the expression of numerous genes. Plants developed effective mechanisms of perception and transduction of sugar signals. Glucose, sucrose, trehalose and other sugars might serve as elicitors of plant sugar signaling. Hexokinase, sucrose and glucose transporters (and specific sugar receptors) have been proposed as components of sugar sensing machinery. Roles of G-proteins and specific serine/threonine kinases and phosphatases in sugar signal transduction in plant cell are discussed. The interaction of sugar signaling pathways with other signal transduction pathways operating in plant cells is emphasized.

Keywords: hexokinase, metabolism regulation, sugar signaling, signal transduction

Summary: Fertilization of a mouse oocyte triggers oscillations of the concentration of free calcium ions in ooplasm ([Ca²⁺]_i ). Calcium oscillations are generated in a process involving inositol 1,4,5-triphosphate (IP3) produced by phospholipase C zeta (PLC zeta), a sperm specific isoform of phospholipase C. Calcium transients last for several hours until the time of pronuclei formation. The ability to generate and sustain long-lasting oscillations of [Ca²⁺]_i is developed in oocytes during meiotic maturation, i.e. in a period between the completion of prophase of the first meiotic division and metaphase of the second meiotic division. This work focuses on the role of sperm-induced oscillations of [Ca²⁺]_i in the activation of the embryo development. The mechanisms of MPF inactivation and block to polyspermy are presented. Moreover, the link between calcium oscillations and ATP synthesis, translation of maternal mRNAs and postimplantation embryo development is described.

Key words: calcium, fertilization, embryonic development, mouse, mammal, meiosis, MPF, block to polyspermy