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The initial response of the body to infection is nonspecific
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This is the ability of
organisms to resist infection by protecting against
disease-causing microorganisms or their toxins that
invade their bodies
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T-lymphocytes and cell
mediated immunity

Lymphocytes respond to an organisms own cells that
have been infected by non-self material from a different
species (like a virus)
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These have different antigens on their cell-surface membrane from the antigens on the organisms own cell
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The body •
also has specific responses that react to specific antigens
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These are produced by stem •
cells in bone marrow
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Associated with humoral immunity = immunity involving antibodies that are present in the body fluids or ‘humour’ such as blood plasma
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pathogens invade body cells or are taken in by
phagocytes
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The phagocyte places antigens from the pathogen on its cell-surface membrane
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Receptors on a specific helper T cell fit exactly
onto these antigens
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This attachment activates the T cell to divide
rapidly by mitosis and form a clone of genetically identical cells
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The cloned T cells:

•

Develop into memory cells that enable a rapid
response to future infections by the same pathogen
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•
The presence of an antigen triggers the production of
an antibody as a part of the bodies defence system
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They are associated with cell-mediated immunity = immunity involving body cells
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Transplanted cells from individuals of the same spe- •
cies have different antigens on their cell-surface
membrane
•

Cancer cells are different from normal body cells and
present antigens on their cell-surface membrane
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How cytotoxic T cells kill infected cells:

These kill abnormal cells and body cells that are
Cells that display foreign antigens on their surface are called infected by pathogens by producing a protein
(perforin) that makes holes in the cell-surface
antigen-presenting cells
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These mean the membrane becomes
T-Lymphocytes will only respond to antigens that are prefreely permeable to all substances and the cell dies
sented on a body cell
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Action of T cells is most effective
munity
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These
against viruses because these replicate inside cells
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There is a vast number of different
types of T cell, each one responding to a different antigen

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