Adaptive acquired Specific immunity Adaptive immunity refers to

Adaptive (acquired, Specific) immunity Adaptive immunity refers to antigen-specific defense mechanisms that take several days to become protective and are designed to react with and remove a specific antigen. This is the immunity one develops throughout life. Adaptive immunity is flexible, specific, and has immunological memory, that is, it can respond more rapidly and vigorously on a second exposure to an antigen. Immunologic memory provides a more powerful response to a repeated exposure to the same foreign substance or antigen. key features of the adaptive immunity ‘specificity + memory’

Cells and molecules of the Adaptive Immune Responses q Lymphocytes: – pluripotent stem cells. . . – B Cells (bone marrow) – T Cells (thymus) Immune Recognition Molecules: q Antigen: a foreign molecule that q Antibodies: antigen-binding immunoglobulin, q Antigen receptors: plasma membrane elicits a response by lymphocytes (virus, bacteria, fungus, protozoa, parasitic worms) produced by B cells receptors on B and T cells T Cell Receptor (TCR), B Cell Receptor (BCR), Major Histocompatibility Complex (MHC)

Principles of Adaptive Immune Responses • Specific recognition of individual antigens by immune cells via antigen receptors • Clonal selection and expansion occurring after antigenic recognition- PRIMARY IMMUNITY – Generation of effector T cells and B cells + Memory T and B cells • Later exposure to the same antigen: SECONDARY (MEMORY) RESPONSE – Rapid proliferation of memory cells

Types of Adaptive Immunity q Cell-mediated immunity (CMI): Refers to T-cell mediated immune response via – Direct lysis of target (infected) cells – Production of cytokines that activate infected cells to kill pathogens Cytotoxic T cell (Tc), Helper T cells (TH) Defense against intracellular pathogens and pathogens that reside inside vesicles of the cell; help to eradicate extracellular bacteria, viruses q Humoral immunity: Refers to antibody-mediated immune response produced by B cells with the help from TH 2 cell – Antibodies bind to whole or fractions of antigens outside cells – Antibodies neutralize and eradicate extracellular pathogens and toxins

Phases of Adaptive Immunity Sequential Phases: q antigen recognition by lymphocytes q activation of the lymphocytes to proliferate and to differentiate into effector and memory cells q elimination of the microbes q decline of the immune response q long-lived memory

Specificity & Memory– properties of the adaptive immunity Specificity : Ability to recognize and respond to many different microbes Memory : Enhanced responses to recurrent or persistent infections “Specificity and Memory” in adaptive immunity • 1 st infection memory 2 nd infection slow response fast response pathogen proliferate killed pathogen

Illustration of Specificity & Memory in adaptive immunity Naive lymphocyte Primary Response Memory Cells Naive Cells

Immunological memory & vaccination • Natural infections: 1 st infection memory slow response pathogens multiply Symptoms/disease 2 nd infection fast response pathogens disposed no disease • Vaccination memory nature infections no disease fast response pathogens disposed no disease

Vaccination protects us from infection by inducing the adaptive immune response, but bypassing the need for a primary infection

Immunological Memory Active memory and immunization • The Ability of the immune system to respond more rapidly and effectively to specific pathogens that have been encountered previously – either by previous infection or by vaccination • Reflection of the pre-existence of clonally expanded lymphocytes (population, pool) with specificity for the antigen.

Passive memory (immunity) Immunity that is present without prior exposure to microbes q Derived from the mother either in uterus or through the milk q During pregnancy, a particular type of antibody, called Ig. G, is transported from mother to baby directly across the placenta. Human babies thus have high levels of antibodies even at birth, with the same range of antigen specificities as their mother. Breast milk also contains antibodies that are transferred to the gut of the infant and protect against bacterial infections until the newborn can synthesize its own antibodies. q The passive immunity is usually short-term, lasting from a few days up to several months q In medicine, protective passive immunity can also be transferred artificially from one individual to another via antibody-rich serum