Answers to the questions
- Provides an immediate nonspecific immune response.
First line of defense is like a moat and high stone walls of castle.
1) Mechanical barriers: skin, mucosa
2) Chemical barriers: The skin and mucous membranes
secrete proteins such as lysozymes or hydrochloric that kill the germs
3) Biological barriers: Living organisms in the body
that compete with pathogens.
Once
the invaders (bacteria, virus, or parasite etc) enter through the cut and get
into the body, they would then encounter the second
line of defense.
Inflammatory response is the first response to infection or injury and is the same
regardless of the type of pathogen. Inflammation is triggered by chemicals
called cytokines and histamines,
which are released when tissues are damaged. The cytokines and histamines cause
changes in the damaged tissue. The changes help remove the cause of the damage
and start the healing process. Another role of cytokines is to attract leukocytes
to the site of inflammation. Some leukocytes are nonspecific and respond in the
same way to most pathogens. Nonspecific leukocytes include monocytes,
macrophages, neutrophils, eosinophils, and basophils. Monocytes, macrophages, and
neutrophils destroy pathogens in the blood and tissues by phagocytosis. Phagocytosis is the process of
engulfing and breaking down pathogens and other unwanted substances. In
addition to phagocytosis, both monocytes and phagocytes produce chemicals such
as cytokines that cause inflammation and fever. A fever is a higher-than-normal
body temperature that may help fight infection.
<phagocytosis by a macrophage>
2.
Activates T and B cells in response to an infection
1. B-cell activation in Humoral
Immune Response
B cells are responsible for the humoral immune response. The humoral immune
response takes place in blood and lymph and antibodies are produced by
activated B-cells, ‘plasma cells’.
2) T-cell activation in cell-
mediated immune response
Activation of T-cells needs other cells help. B
cells or leukocytes such as macrophages engulf pathogens in phagocytosis and display
parts of the pathogens’ antigens on their surface. The cells are then called
antigen-presenting cells. When a naïve T cell encounters
one of these cells with an antigen matching its own, it begins the activation
process. After T cells are activated, the various types of T cells play
different roles in the immune response.
3. Responds to a later exposure to the same infectious agent
The immune response is specific to a
particular pathogen, and it allows the immune system to “remember” the pathogen
after the infection is over. Memory
cells are activated B or T cells that retain a “memory” of a specific
pathogen long after an infection is over .If the pathogen tries to invade the body
again, the immune system can launch a
much faster, stronger attack. This lets the immune system destroy the pathogen
before it can cause harm.
- Disinguishes self from nonself
Immune
cells do not actually recognize and respond to pathogens but to the antigens (antibody + generator) they
carry. Antigens are protein molecules
that the immune system recognizes as nonself. Antigens include proteins on
pathogens, cancer cells, and the cells of transplanted organs. Both B and T
cells can “recognize” specific antigens because they have receptor molecules on
their surface that bind to particular antigen molecules or pieces of antigen
molecules. As shown in the figure, the fit between a receptor molecule and a
specific antigen is like a lock and key.
Receptors on each B or T cell recognize and bind to just one type of antigen. The human body makes lymphocytes with
receptor sites for a huge number of possible antigens that may be encountered
throughout a person’s life.
