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(BQ) Part 2 book "How the immune system works" presents the following contents: Secondary lymphoid organs and lymphocyte trafficking, restraining the immune system, self tolerance and MHC restriction, immunological memory, the intestinal immune system, vaccines, the immune system gone wrong, cancer and the immune system, immunodeficiency,. | LECTURE 7 Secondary Lymphoid Organs and Lymphocyte Trafficking HEADS UP The secondary lymphoid organs are strategically placed to intercept invaders which penetrate our barrier defenses. During an infection rare T cells must find antigen presenting cells that display their cognate antigen and B cells must encounter helper T cells which can assist them in producing antibodies. The secondary lymphoid organs make it possible for antigen presenting cells T cells and B cells to meet under conditions that favor activation. The trafficking of immune system cells throughout our body is controlled by the modulated expression of adhesion molecules on the surface of these cells. Virgin and experienced lymphocytes move in different traffic patterns. INTRODUCTION In earlier lectures we discussed the requirements for B and T cell activation. For example in order for a helper T cell to assist a B cell in producing antibodies that Th cells must first be activated by finding an antigen presenting cell which is displaying its cognate antigen. Then the B cell must find that same antigen displayed in a fashion which crosslinks its receptors. And finally the B cell must find the activated Th cell. When you recognize that the volume of a T or B cell is only about one one-hundred-trillionth of the volume of an average human the magnitude of this finding problem becomes clear. Indeed it begs the question How could a B cell ever be activated The answer is that the movements of the various immune system players are carefully choreographed not only to make activation efficient but also to make sure that the appropriate weapons are delivered to the locations within the body where they are needed. Consequently to really understand how this system works one must have a clear picture of where in the body all these interactions take place. So it is time now for us to focus on the geography of the immune system. The immune system s defense against an attacker actually has three phases recognition
