《USMLE Step 1 Immunology and Microbiology》.pdf

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The Immune System
Define and describe the components of the immune system Discriminate between innate and acquired immunity
The Immune System The immune system is designed to recognize and respond to non-self antigen in a coordinated manner. Additionally, it recognizes and eliminates cells that are diseased, damaged, distressed, or dying. The immune system is divided into 2 complementary arms: the innate and the adaptive immune systems.
INNATE IMMUNITY Innate immunity provides the body?s first line of defense against infectious agents. It involves several defensive barriers: Innate immune defenses have the following characteristics in common:
ADAPTIVE IMMUNITY The components of the adaptive immune response are B and T lymphocytes and their effector cells. Adaptive immune defenses have the following characteristics in common: The features of adaptive immunity are designed to give the individual the best possible defense against disease. Characteristics Innate Adaptive Specificity For pathogen-associated molecular patterns (PAMPs) For specific antigens of microbial and nonmicrobial agents Diversity Limited High Anatomic and physical (skin, mucous membranes and normal flora) Physiologic (temperature, pH, anti-microbials and cytokines) Complement Cellular: phagocytes and granulocytes Inflammation Are present intrinsically with or without previous stimulation Have limited specificity for shared microbe and cellular structures (pathogen-associated molecular patterns [PAMPs] and damage-associated molecular patterns [DAMPs]) Have limited diversity as reflected by a limited number of pattern recognition receptors Are not enhanced in activity upon subsequent exposure?no memory Each B and T lymphocyte is specific for a particular antigen As a population, lymphocytes have extensive diversity Are enhanced with each repeat exposure�?immunologic memory Are capable of distinguishing self from non-self Are self-limiting Specificity is required, along with immunologic memory, to protect against persistent or recurrent challenge. Diversity is required to protect against the maximum number of potential pathogens. Specialization of effector function is necessary so that the most effective defense can be mounted against diverse challenges. The ability to distinguish between self (host cells) and non-self (pathogens) is vital in inhibiting an autoimmune response. Self-limitation allows the system to return to a basal resting state after a challenge to conserve energy and resources and to avoid uncontrolled cell proliferation resulting in leukemia or lymphoma


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