Immune System - BLOCK QUIZ ANSWERS
Briefly
describe the process of inflammation, mention especially the signs, events,
cells and mediators associated with it.
Inflammation
is a natural process that occurs after tissue damage or injury. It is a
non-specific response and its main observable signs are redness, swelling, pain
and heat. A combination of these factors may result in either significant or
relative loss of function associated with the inflamed area.
The
agents involved during inflammation are various macrophages, white blood cells
mainly neutrophils and monocytes which have phagocytic properties, mast cells
and natural killer cells. Natural killer cells are cells that act in response to
virus infected or tumor cells and they function in order to kill these cells to
stop the spreadage of the disease.
There
are a number of events that occur during inflammation, which collectively help
the body to fight against the tissue injury or damage caused chemically,
physically or pathogenically. The redness and the swelling is primarily caused
by the vasodilation and increased vascular permeability. This is because, the
body brings in more white blood cells and the required nutrients in order to
induce tissue repair and regrowth. The second event is the migration of the
phagocytes such as macrophages, monocytes and neutrophils via the blood to
phagocytose the infected cells and bacteria. This is brought about by chemotaxis,
the relative attraction of the phagocytes to the site of inflammation. After
ingestion of the waste cells, tissue repair begins. During inflammation there
are a variety of chemical mediators that induce inflammation.
The
chemical mediators are as follows. Histamine is released by damaged mast cells,
basophils and platelets. Leukotrienes are another variety which are largely
derived from membrane lipids of mast cells and basophils. Kinins are another
variety of mediators which are found in inactive forms among the plasma and are
also released by neutrophils. Prostaglandins are another forms which are derived
from membrane lipids of all damaged cells and especially neutrophils. All four
chemical mediators have an effect on the vascular changes during inflammation,
while the last three have an effect on the chemotactic activity of the
phagocytes involved. The last two mediate the pain response as a result of
inflammation.
Major Points: What is inflammation?, Major signs, cells involved in the inflammatory response, the events of inflammation, chemotaxis, chemical mediators involved > derivation > effects on the cardinal signs. Possibly add in information about appropriate treatments > RICE
State
the targets of humoral immunity and briefly outline its basis. Refer
particularly to the nature of antigens and antibodies and to the cellular
interactions that are necessary for a humoral immune response to occur.
The
targets of humoral immunity are the extracellular antigens (found in the
extracellular fluid). The ultimate aim of this type of response, known as
antibody mediated response, is for antibodies to be produced for a particular
antigen to form an antibody-antigen complex which can be phagocytosed by
circulating macrophages. Antigens are substances that initiate an immune
response, and are classified as non-self and destructive to the cells of the
body. When they make entry into the body tissues, these are phagocytosed by the
antigen presenting cells. Antigen presenting cells partially digest these
antigens and have the portion which causes the immune response to be projecting
out of the cell membrane. These regions are referred to as haptens. APC’s have
specific membrane proteins called MHC – II proteins. These are specific to
these cells, and they bind to the hapten part of the injested antigen, forming a
protein-hapten complex. If circulating T-Helper cells have specific receptors to
this particular hapten, then they also bind to this complex. The interaction
between the t-helper cells and the hapten-protein complexes causes the release
of cytokines by the t-helper cells, and also stimulates more t helper cells to
proliferate. This in turn stimulates b lymphocytes and activates these cells.
Cytokines
are special substances released in order to have an effect on surrounding cells.
They cause differentiation and mitosis of surrounding cells. In this case a
particular type called interleukins are released and these cause the
proliferation of b-lymphocytes. B lymphocytes then become plasma cells and/or
memory b cells, which are the effector cells of the humoral immune response, and
these cells secrete specific antibodies for the specific antigen that has caused
this response. B memory cells, have the antigen receptors already present on
their membranes and quickly act in the case of a second antigenic response.
Antibodies
are special proteins which are structurally made up of two chains of
polypeptides which are linked together by disulfide bonds. The antibodies
circulate in extracellular fluid, looking to bind to antigens. These antibodies
bind to the antigen complex, and neutralize them. Then circulation macrophages
ingest the remains, and the humoral immune response is complete. There are
several classes of antibodies which are used in different circumstances.
For
a humoral response to take place, b lymphocytes must be stimulated in order to
become plasma cells and then antibodies must be secreted. For this to occur,
this requires the presence of b lymphocytes, antigens, antigen presenting cells,
t helper cells, special membrane proteins called MHC-II proteins and cytokines
must be released from the t helper cells.
Major Points (Humoral Immunity): Antigen present > APC partially ingest and digest the antigens > hapten projects out > special MHC-II proteins on membranes bind to these hapten > complex formed > receptors on t helper cells bind to the hapten-antigen complex > then cause release of cytokines > cell to cell contact and chemical co-stimulation (2nd co-stimulation) causes activation of b lymphocytes (have receptors to antigens) > stimulated to become plasma cells or memory cells > secrete antibodies > special structure and function of antibodies > what they do > finally macrophages ingest the neutralized antibody antigen complex.
State
the targets of cell mediated immunity and briefly outline its basis, including
the role of MHC proteins and the cellular interactions that necessary for a cell
mediated immune response to occur.
Cell
mediated immunity is similar to humoral immunity in many ways, the targets
involved the intracellular antigens. This acts directly on the cells, compared
to humoral which involved production of antibodies that bind to antigens and
makes them nonfunctional. When an antigen enters the body tissues, Antigen
presenting cells engulf them and then partially digest them, leaving a portion
which projects out of the cell membrane. This portion is the immune response
causing agent is referred as a hapten. The APC’s have special membrane
proteins in addition to the normal MHC-1 proteins, and these are the MHC-II
proteins. These proteins form a hapten-protein complex. Circulating t helper
cells have special receptors on their cell membrane, and these bind to the
hapten-protein complex if the receptors match the antigen engulfed. The
triggering of this response causes release of several cytokines (mainly
interleukin 2) by the t helper cells.
Cytokines
are special proteins released by certain cells and these cause the profileration
and differentiation of surrounding cells of the same type. These act in
co-stimulation and bring about an increased cell population. In cell mediated
immunity, the cytokines induce further proliferation and differentiation of t
helper cells and this co-stimulates the t lymphocytes to become cytotoxic t
cells. The activation of cytotoxic t cells, brings about the cell mediated
response. The cytotoxic t cells directly attack the antigens and lyse them. Also
t memory cells are present and these have the receptors to that particular
antigen, so that future entry of the same antigen will bring about a faster,
more prolonged and destructive immune response. These cells have the same
function as b memory cells in humoral immunity response.
Major points (Cell-Mediated Immunity): Antigen present > APC partially ingest and digest the antigens > hapten projects out > special MHC-II proteins on membranes bind to these hapten > complex formed > receptors on t helper cells bind to the hapten-antigen complex > then cause release of cytokines > cell to cell contact and chemical co-stimulation (2nd co-stimulation) causes activation of cytotoxic t cells > more t cells formed and memory t cells > t cells attack the antigen