The specific response to infection

Biology Unit 4

The specific response to infection

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Biology Unit 4
Revision Notes
Topic 6: Infection, Immunity and Forensics
14. Distinguish between the roles of B cells (including
B memory and B effector cells) and T cells (T helper, T
killer and T memory cells) in the body's immune
The immune system is the specific response of the body to invasion by pathogens. It enables the
body to recognise anything that is non-self and to remove it from the body as efficiently as possible.
There are two main types of white blood cells involved in the immune system. Lymphocytes are
agranulocytes, made in the white bone marrow of the long bones. They move around the body in the
blood and lymph, and are involved in recognising and responding to foreign antigens. Macrophages
are also agranulocytes. They have left the bloodstream and move freely through the tissue.
The immune system of the body has 4 key characteristics:
It can distinguish "self from non-self"
It is specific ­ it responds to specific foreign cells
It is diverse ­ it can recognise an estimated 10 million different antigens
It has immunological memory ­ once you have met and responded to a pathogen, you can
respond rapidly if you meet it again
There are two main types of lymphocytes involved in the immune system : T cells and B cells
T cells
T cells or T lymphocytes play a central role in cell-mediated immunity. They can be distinguished
from other lymphocyte types such as B cells and natural killer cells (NK cells) by the presence of a
special receptor on their cell surface called T cell receptors (TCR). The T cells originate and mature
from the thymus. Several different subsets of T cells have been discovered, each with a distinct
T helper ­ assist other white blood cells in immunologic processes, including maturation of B
cells into plasma cells and memory B cells, and activation of cytotoxic T cells and
macrophages, among other functions. These cells are also known as CD4 T cells because
they express the CD4 protein on their surface. Helper T cells become activated when they
are presented with peptide antigens by MHC class II molecules that are expressed on the
surface of APCs. Once activated, they divide rapidly and secrete small proteins called
cytokines that regulate or assist in the active immune response.
Natural killer ­ Natural killer T cells (NKT cells) are a special kind of lymphocyte that bridges
the adaptive immune system with the innate immune system. Unlike conventional T cells that
recognise peptide antigen presented by MHC molecules, NKT cells recognise glycolipid
antigen presented by a CD1d molecule. Once activated, these cells can produce chemicals
that destroy pathogens.
Memory ­ Memory T cells are a subset of antigen-specific T cells that persist long-term after
an infection has resolved. They quickly expand to large numbers of effector T cells upon
re-exposure to their cognate antigen, thus providing the immune system with "memory"
against past infections.
Text Book: p. 100 ­ 103

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Biology Unit 4
Revision Notes
B cells
B cells are lymphocytes that play a large role in the humoral immune response. The principal
functions of B cells are to make antibodies against antigens, perform the role of APCs and eventually
develop into memory B cells after activation by antigen interaction. They do not produce antibodies
until they become fully activated. Each B cell has a unique receptor protein (B cell receptor ­ BCR) on
its surface that will bind to one particular antigen.…read more

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Biology Unit 4
Revision Notes
The humoral response of the immune system consists of two main stages: the T helper activation
stage and the effector stage.
A pathogen enters the body and is brought into contact with macrophages where it is engulfed by
The macrophage presents the antigens from the bacterium on MHCs. The complex becomes an APC
CD4 receptors allow the T helper cell to bind to the specific antigen of the complex.…read more


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