Cancer is a result of genetic changes in the cells, which can
also be a consequence of external influences. Some types of cancer cells
are able to deactivate the cellular death program which normally ensures
that cells die when they are no longer needed by the organism.
Capsule: Some bacteria have a capsule made of carbohydrates
which protects them from phagocytosis. Bacteria of this type can cause
extracellular infections. Phagocytes cannot ingest and destroy them
until they are first bound by antibodies and attacked by components
of the complement system which are produced as part of an acquired immune
response.
CD4 T helper cells are CD4 T cells which support the B cells
in their antibody reaction against an antigen.
Cellular immune response: The cellular immune response includes
all adaptive immune reactions in which antigen-specific T cells play
a key role. They include all parts of the adaptive immune system which
cannot be transferred with the serum antibodies - the primary elements
of the humoral immune response - to a non-immune recipient.
Cellular immunology is the study of the cellular basics of immunity.
Central lymphatic organs: The central lymphatic organs are where
the lymphocytes develop. In humans, the B cells are formed in bone marrow,
while the T cells form in the thymus gland from precursor cells which
come from the bone marrow.
Clone: A clone is a population of cells which all stem from
a common precursor cell.
Complement: A group of proteins required if certain antigen-antibody
reactions are to take place is called a complement.
Complement receptors are surface proteins of various cells.
They recognize and bind complement proteins, which themselves are bound
to a pathogen. Complement receptors on phagocytes enable these cells
to recognize and destroy pathogens enveloped by complement proteins.
Complement system: The complement system consists of a series
of plasma proteins which together attack extracellular pathogens. It
is spontaneously activated for some pathogens, in other cases by the
binding of antibodies to the pathogen. The envelope of complement proteins
which then surrounds the pathogen simplifies its destruction by phagocytes.
The complement proteins alone can also kill the pathogen.
Congenital immunity: The early phases of a defence reaction
come from congenital immunity; a wide range of congenital resistance
mechanisms recognize a pathogen and react to its presence. Congenital
immunity exists in all individuals and at all times; it does not increase,
even if there is repeated contact with the pathogen, and does not distinguish
among various pathogens. A defence reaction brought about by congenital
immunity is normally followed by an acquired immunity response based
on the clonal selection of specific lymphocytes and leading to long-term
protection from a renewed infection.
Contact allergy: A contact allergy is a form of delayed hypersensitivity
in which the T cells react to antigens which enter the body through
the skin.
Co-receptor: A co-receptor is a cell surface protein which increases
the sensitivity of an antigen receptor to its antigen by binding to
neighbouring ligands. It participates in the signal cascade which leads
to activation. CD4 and CD8 are examples of MHC-binding co-receptors
on T cells.
Corticosteroids are steroids (hormones) such as cortisone formed
in the adrenal glands. Corticosteroids can kill lymphocytes, especially
maturing thymocytes, by triggering apoptosis. They are administered
as medications to inhibit inflammation and as immunosuppressives.
Cortisone is a substance which inhibits
inflammation.
Cross reaction: In a cross reaction, an antibody binds to an
antigen which was not used in the production of the antibody. If an
antibody which has been specifically produced against antigen A binds
to antigen B, there is said to have been a cross reaction with antigen
B. Generally speaking, this expression is used to describe the reaction
of antibodies or T cells to antigens other than the ones that triggered
the reaction.
Cross test: Cross tests are used for blood typing and histocompatibility
tests to determine if a donor or recipient has antibodies against the
cells of the other person which could cause problems during a transfusion
or transplant.
Cyclosporin A is an effective immunosuppressive
medication. It inhibits the signal transmission via the T cell receptors
and thus prevents the activation of the T cells so that they cannot
exercise their effector functions.
Cytokines are proteins from cells which
influence the behaviour of other cells. Cytokines produced by lymphocytes
are often called lymphokines or interleukins (abbreviated IL). Cytokines
work through specific receptors on their target cells.
Cytotoxic T cells are T cells which
can kill other cells. Most cytotoxic T cells are CD8 T cells aimed at
MHC class I molecules, but CD4 T cells can also kill other cells in
some cases. Cytotoxic T cells are important for defence against cytosolic
pathogens.
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