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Lecture

Lecture_4_Summary.pdf

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Department
Immunology and Infection
Course
IMIN200
Professor
All Professors
Semester
Fall

Description
LECTURE #4 – INTRODUCTION TO ADAPTIVE IMMUNITY After studying lecture #4, you should be familiar with the following concepts. 1. Adaptive Immunity. The adaptive immune response is an evolutionary newcomer that is restricted to non-cartilaginous jawed vertebrates. In contrast to innate immunity, adaptive immune responses are not restricted to specific classes of microbial molecules and adaptive immune receptors are not encoded within the germline. A further valuable feature of adaptive immune responses is that they improve or “adapt” upon repeated exposure to a given foreign toxin or microbe. 2. Antigens. Adaptive immune responses are stimulated by “antigens”. Originally defined as “antibody generating” an antigen is now loosely defined as any molecule that simulates an immune response from B or T lymphocytes. Antigens are recognized directly by B Cell Receptors (BCR) on the surface of B cells. Alternatively, antigens are presented to T Cell Receptors (TCR) on the surface of T cells by Antigen Presenting Cells (APC). The BCR recognizes three-dimensional structures and mediates humoral responses to extracellular antigens. In contrast, the TCR recognizes linear or two- dimensional peptide antigens and mediate cellular responses to intracellular antigens. 3. Stages of an adaptive immune responses. The adaptive immune response proceeds through a discreet series of steps. First the foreign antigen is detected directly by a BCR or by a TCR interacting with and APC. Second the lymphocyte becomes activated and undergoes clonal expansion. Activation requires two signals: detection of antigen and a second signal such as a cytokine from the innate immune response or a microbial product. During clonal expansion the active B and/or T cells undergoes multiple rounds of replication. The result is an expanded population of a clone of B or T cells with receptors specific to the foreign antigen. B cells and T cells that don’t recognize the antigen will not undergo clonal expansion. The activate
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