Download The Human Immune response

NONSPECIFIC DEFENSES
The nonspecific immune system consists of two lines of defense.
First Line of Defense
The first line of nonspecific defense is a barrier that helps prevent pathogens from entering the body. The
body has several different types of barriers:
• Skin that blocks pathogens
• Mucous membranes that release mucus and trap microbes
• Cilia in the respiratory system that sweep out mucus with its trapped microbes
• Stomach acid that kills germs that enter through the nose and mouth
Second Line of Defense
Microbes that get into the body encounter the second line of nonspecific defense.
It is meant to limit the spread of invaders in advance of specific immune responses.
There are three types.
1. Inflammatory response. It is characterized by swelling, redness, soreness, and increased temperature in
the area. The purpose of this process is to increase the blood supply to the area, thus increasing
nutrients—including oxygen, and white blood cells to fight disease. The inflammatory response works in
several ways.
• Histamine triggers vasodilation (enlargement of blood vessels), which increases blood supply to the
area, bringing more phagocytes to gobble up germs. Histamine is also responsible for the symptoms of
the common cold: sneezing, coughing, redness, and itching and runny nose and eyes— all an attempt to
rid the body of invaders.
• Increased body temperature speeds up the immune system and makes it more difficult for microbes to
function.
2. Phagocytes. These gobble up invading microbes. Macrophages (“gia eaters”) are a type of white blood
cell that extend pseudopods and en
huge numbers of microbes over a long period of time.
3. Interferons. These chemicals are released by the immune system to bloc against viral infections.
SPECIFIC DEFENSES—THIRD LINE OF DEFENSE
The third line of defense is specific and consists of lymphocytes. There are two typ of lymphocytes, B
lymphocytes and T lymphocytes. Both originate in the bc marrow. Once mature, both cell types circulate
in the blood, lymph, and lympha tissue: spleen, lymph nodes, tonsils, and adenoids. Both recognize
different spec antigens (germs) (Strictly speaking, an antigen is anything that triggers an imm response).
1. B lymphocytes. These produce antibodies against a specific antigen in is called a humoral response.
2. T lymphocytes. These fight pathogens by hand-to-hand combat in wh called a cell-mediated response.
Antibodies
Antibodies are part of the third line of defense—the specific immune response. antibody has the ability to
bind to only one particular antigen. For example, bodies against influenza bind to and neutralize only
influenza virus; they have no effect on the polio virus. Antibodies neutralize antigens by binding to them
and becoming an antigen-antibody complex that can then be gobbled up by a phage
Clonal Selection
Clonal selection is a fundamental mechanism in the development of immunity Antigens that have entered
the body bind to specific B or T lymphocytes. Once a lymphocyte has been selected, it becomes very
metabolically active, proliferates (clones thousands of copies of itself), and differentiates into plasma cells
and memory cells.
PLASMA CELLS
These fight antigens immediately in what is called the primary immune response. They do not live long.
MEMORY CELLS
These fight the same antigens that plasma cells do, but they remain circulating in the blood in small
numbers for a lifetime. You have memory cells circulating in your blood that are specific for every viral
infection you have ever been ill with and against every disease against which you have been vaccinated.
You have memory cells specific for mumps, measles, rubella, polio, and so on. The capacity of the
immune system to generate a secondary immune response is called immunological memory. The
immunological memory is the mechanism that prevents you from getting any specific viral infection, such
as chicken pox, more than once.
TYPES OF IMMUNITY
Passive immunity is temporary
• Antibodies are borrowed and do not survive for long.
• Examples are maternal antibodies that pass through the placenta to the developing fetus or that pass
through breast milk to the baby. The first milk that a newborn receives from mother is called colostrum
and is 100 percent antibodies.
Active immunity is permanent.
• You make the antibodies yourself
• An individual makes his or her own antibodies after being ill and recovering or after being given an
immunization or vaccine. A vaccine contains either dead or live viruses or enough of the outercoat of a
virus to stimulate a fill immune response and to impart lifelong immunity.
ABO Blood Types ABO antibodies circulate in the plasma of the blood and bind with ABO
antigens in the event of an improper transfusion. Certain danger from a transfusion comes when the
recipient has antibodies to the donors antigens. However, before someone receives a transfusion of
blood, samples of the recipients and the donors blood must be mixed in the lab to determine and ensure
compatibility This is called a
cross-match.
Blood type 0 is known as the universal donor because it has no blood cell antigens to be clumped by the
recipient’s blood. Blood type AB is known as the universal recipient because there are no antibodies to
clump the donor’s blood.
AIDS Virus
AIDS stands for acquired immune deficiency syndrome. People with AIDS are highly susceptible to
opportunistic diseases, infections, and cancers that take advantage of a collapsed immune system. The
virus that causes AIDS, HIV (human immunodeficiency virus) mainly attacks helper T cells. HIV is a
retrovirus. Once inside a cell, it reverse transcribes itself. That means that the viral RNA uses the enzyme
reverse transcriptase to make DNA. This is the opposite of the typical DNA transcribing mRNA. The host
cell then integrates this newly formed DNA into its own genome.
OTHER INFORMATION RELATED TO IMMUNITY
• Allergies are hypersensitive immune responses to certain substances called allergens. They involve the
release of excessive amounts of histamine, an anti-inflammatory agent, which causes blood vessels to
dilate. A normal allergic reaction involves redness, runny nose, and itchy eyes. Taking antihistamines can
normally can counteract these symptoms. However, sometimes an acute allergic response can result in a
life-threatening response called anaphylactic shock that can result in death within minutes. • Antibiotics
are medicines that kill bacteria or fungi. Although vaccines are given to prevent illness caused by viruses,
antibiotics are administered after a person is sick. They cure the disease.
• Vaccines prevent viral infections. There is no treatment for viral infections, like there is for bacterial
infections. New vaccines and treatments are always being developed. In fact, a new vaccine against a
virus that causes cervical cancer has recently been developed. However, the best method for fighting any
disease is to prevent it.
Autoimmune diseases such as multiple sclerosis, lupus, arthritis, and juvenile diabetes are caused by a
terrible mistake of the immune system. The system cannot properly distinguish between self and nonseif.
Instead, it perceives certain structures in the body as nonself and attacks them. In the case of multiple
sclerosis, the immune system attacks the myelin sheath surrounding certain neurons.