and back again as often as 1-2 times per day. Since only about one in 105 lymphocytes recognizes a particular antigen, it would appear that a large number of T or B cells must contact antigen on a given antigen-presenting cell within a short time in order to generate a specific immune response. The odds of the small percentage of lymphocytes committed to a given antigen actually making contact with that antigen when it is present are elevated by the extensive recirculation of lymphocytes. The likelihood of such contacts is profoundly increased also by factors that regulate, organize, and direct the circulation of lymphocytes and antigen-presenting cells.
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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.