In humans, less than 5% of T cells bear the 78 heterodimer, and the percentage of 78 T cells in the lymphoid organs of mice has been reported to range from 1% to 3%. In addition to their presence in blood and lymphoid tissues, they also appear in the skin, intestinal epithelium, and pulmonary epithelium. Up to 1% of the epidermal cells in the skin of mice are 78 T cells. In general, 78 T cells are not MHC-restricted, and most do not express the coreceptors CD4 and CD8 present on populations of ap T cells. Although the potential of the 7 and 8 TCR loci to generate diversity is great, very little diversity is found in this type of T cell. In fact, as pointed out in Chapter 9, most of the 78 T cells in humans have an identical combination of 78 chains (79 and 82).
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.