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Adaptive Immunity Overview

• Adaptive immunity occurs in vertebrates and involves specific recognition of pathogens.

• It operates alongside the innate immune response simultaneously.

• The two primary components of adaptive immunity are the humoral response (antibody-mediated defense) and cell-mediated response.

Key Components of Adaptive Immunity

• Pathogen Recognition: Antibodies provide pathogen-specific recognition, crucial for identifying harmful entities.

• Lymphocytes: Key players include T cells and B cells, types of white blood cells that combat infections rather than red blood cells, which function mainly to carry oxygen.

T Cells and B Cells

• T Cells: Mature in the thymus gland; involved in cell-mediated immunity.

• B Cells: Responsible for antibody production; differentiate into plasma cells and memory B cells.

Antigens

• Definition: Antigens are substances that elicit an immune response; they can be proteins, polysaccharides, or even blood type mismatches.

• Antigens stimulate the production of antibodies, creating an antibody-antigen complex in some cases, relevant for blood transfusions.

• They are usually large molecules recognized by the immune system as foreign.

Antigen Recognizers on White Blood Cells

• White blood cells have surface structures called antigen receptors manly involved in the binding of specific epitopes from antigens.

• Epitopes: Small portions of antigens recognized by B cells and T cells, essential for the immune response.

• B cell antigen receptors contain constant and variable regions; the variable regions are unique to each B cell.

Structure of B Cell Antigen Receptors

• Y-shaped proteins consisting of two heavy chains and two light chains.

• Constant Region: Common to all B cell receptors, facilitating basic structure consistency.

• Variable Region: Unique to each B cell, generated randomly; crucial for specificity in binding to antigens.

B Cell Activation and Clonal Selection

• Upon binding to a matching epitope, B cells become activated and undergo clonal selection, producing numerous identical cells with the specific receptors for that antigen.

• The antibodies produced are called immunoglobulins, which circulate in the bloodstream to bind to antigens.

Memory B Cells

• Some activated B cells become memory B cells, which persist in the body for quicker responses during subsequent infections with the same pathogen.

T Cell Activation and Function

• Similar to B cells, T cells activate upon recognizing antigens presented by Major Histocompatibility Complex (MHC) molecules on infected cells.

• Helper T Cells: Assist in activating other immune cells, including B cells, by secreting cytokines and promoting clonal expansion.

• Cytotoxic T Cells: Target and kill infected cells; they release perforins to create holes in the target cell membranes and granzymes to induce apoptosis.

Immune Responses

• Primary Immune Response: Initial response upon first exposure to an antigen; slower response as B and T cells need time to activate and clone.

• Secondary Immune Response: Faster response upon re-exposure to an antigen due to memory cells; produces more antibodies more quickly than the primary response.

Immunity Types

• Active Immunity: Developed through exposure to antigens; includes responses from natural infections or vaccinations.

• Passive Immunity: Involves gaining pre-formed antibodies from another individual; occurs naturally through maternal antibodies or through treatments such as antivenom.

Conclusion

• Understanding the mechanics of the immune response, including the roles of B and T cells and how immune memory is established, is critical for immunology and vaccine development.