Immunity
The Language of Cells in Immunity
For almost 100 years scientists have known that certain cells in an animal could secrete substances that affected various processes in other, target cells, for example, metabolism, physiology, or differentiation; however, the means of this communication between cells remained a mystery. Much of the shroud was lifted by more recent discoveries. Specific signal molecules, often proteins or peptides, are secreted by certain cells. Target cells have receptors protruding through their outer membranes that specifically bind the signal molecules and only those molecules. Binding of a signal causes changes in the part of the receptor molecule (or in an associated membrane protein) that extends into the cytoplasm, and this initiates a cascade of activations involving protein kinases and phosphorylases (enzymes that transfer phosphate groups). Transcription factors are mobilized. In the nucleus the transcription factors initiate transcription of formerly inactive genes, leading to synthesis of the products they encode.
We now know that hormones affect target cells by this mechanism, and it is also the scheme by which cells of the immune system communicate with each other and with other cells. Signal molecules of the immune system are called cytokines. Cytokines and their receptors are the language of communication in the immune system. They perform an intricate and elaborate ballet of activation and regulation, causing some cells to proliferate, suppressing proliferation of others, and stimulating secretion of additional cytokines or defense molecules. Precise signalling among cells and exact performance of their duties are essential to maintainence of human health and defense against invading viruses, bacteria, and parasites and for prevention of unrestrained cell division, as in cancer. Successful establishment of invaders in our bodies depends on evasion or subversion of our immune system, and inappropriate response of immune cells may itself produce disease. We have learned to manipulate the immune response so that we can transplant organs between individuals, but complete failure in its cell communication results in profound disease, such as AIDS.
The immune system is located throughout the body of an animal, and it is as crucial to survival as the respiratory, circulatory, nervous, skeletal, or any other system. Every animal’s environment is filled with an incredible number of parasites and potential parasites: flatworms, nematodes, arthropods, single-celled eukaryotes, bacteria, and viruses. Whether any parasite can survive in that animal (the host), and severity of the disease the parasite may cause, depends largely on the response of the host defense system.
For almost 100 years scientists have known that certain cells in an animal could secrete substances that affected various processes in other, target cells, for example, metabolism, physiology, or differentiation; however, the means of this communication between cells remained a mystery. Much of the shroud was lifted by more recent discoveries. Specific signal molecules, often proteins or peptides, are secreted by certain cells. Target cells have receptors protruding through their outer membranes that specifically bind the signal molecules and only those molecules. Binding of a signal causes changes in the part of the receptor molecule (or in an associated membrane protein) that extends into the cytoplasm, and this initiates a cascade of activations involving protein kinases and phosphorylases (enzymes that transfer phosphate groups). Transcription factors are mobilized. In the nucleus the transcription factors initiate transcription of formerly inactive genes, leading to synthesis of the products they encode.
We now know that hormones affect target cells by this mechanism, and it is also the scheme by which cells of the immune system communicate with each other and with other cells. Signal molecules of the immune system are called cytokines. Cytokines and their receptors are the language of communication in the immune system. They perform an intricate and elaborate ballet of activation and regulation, causing some cells to proliferate, suppressing proliferation of others, and stimulating secretion of additional cytokines or defense molecules. Precise signalling among cells and exact performance of their duties are essential to maintainence of human health and defense against invading viruses, bacteria, and parasites and for prevention of unrestrained cell division, as in cancer. Successful establishment of invaders in our bodies depends on evasion or subversion of our immune system, and inappropriate response of immune cells may itself produce disease. We have learned to manipulate the immune response so that we can transplant organs between individuals, but complete failure in its cell communication results in profound disease, such as AIDS.
The immune system is located throughout the body of an animal, and it is as crucial to survival as the respiratory, circulatory, nervous, skeletal, or any other system. Every animal’s environment is filled with an incredible number of parasites and potential parasites: flatworms, nematodes, arthropods, single-celled eukaryotes, bacteria, and viruses. Whether any parasite can survive in that animal (the host), and severity of the disease the parasite may cause, depends largely on the response of the host defense system.
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