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Lecture 10

PSL201Y1 Lecture Notes - Lecture 10: Thymus, Immunoglobulin Light Chain, Mast Cell

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Michelle French

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PSL201 Week 10 Part A Reading Notes- Specific Immunity (pgs. 681-691)
Second type of defense is specific immune responses (adaptive immunity) come into play after nonspecific
responses have already begun and are much slower... mediated by lymphocytes which are very selective
2 Main Types of Specific Immunity
- Humoral Immunity: b cell mediated, B lymphocytes developed into plasma cells that secrete
Defend against extracellular molecules- bacteria, toxins, and viruses in body fluids
- Cell-mediated Immunity- T cell mediated, certain t lymphocytes develop into active cytotoxic t cells
which bind to and kill abnormal cells by lysis
Call cell-mediated because cytotoxic t cells must come into direct contact with their targets to act on
them. Defend against molecules that are inside the cells
Part of reaction to transplants and cancer cells
Characteristics of Specific Immunity
1. Specificity- B and T cells bind and respond to foreign molecules known as antigens
- Antigens: complex proteins and polysaccharides of foreign invader or tumor cell. Each
antigen has a unique structure and contains different recognition sites called epitopes
- Epitopes are recognized by specific lymphocytes which then target the invaders
bearing that epitope for destruction
- B and T cells are able to recognize specific antigens because they have antigen-binding
proteins called antigen receptors
- All receptors on B and T cells bind to a specific bind to a specific antigen
Antibody Structure
- Y shaped molecule consisting of 4 protein chains: 2 identical heavy chains & 2
identical light chains
- Each antibody consists variable regions (V): differs for different antigens, gives
specific to antigen-binding site. Make up top part of the Has two antigen-
binding site thus, each antibody molecule can bind two epitopes of the same
- Each antibody consists constant regions (C): same within a class of antibodies, amino acid sequences
in these regions vary from antibody to antibody
2. Diversity: individual B and T cells recognize different antigens, B and T cells have a different shape of
the variable region
- When a particular microorganism invades the body, it interacts with and
activates only those T or B cells that have receptors specific for the
antigens the microorganisms possesses.
- The foreign antigen triggers an immune response against itself, induces the B or T
cells to proliferate and differentiate, this antigen-driven activation of lymphocytes
is called clonal selection
Two types of Cells formed Upon Activation
- Effector cells: short-lived cells hat combat the same antigen that stimulated their
production (eg. Plasma cells)
- Memory cells: long-lived cells bearing membrane receptors specific for the same
antigen (eg. Memory B cells)
3. Memory: memory cells responsible for more rapid and greater secondary immune
- once you get rid of the infection, the memory cells will allow you to respond to the
same infection much faster next time you get the same infection
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