Immune system
Immune system
A fully functional immune system can distinguish healthy tissue from
unwanted substances. If it detects an undesirable substance, it will mount an
immune response — a complex attack to protect the body from invaders like
bacteria, viruses, fungi, and parasites. It also recognises and removes dead
and faulty cells.
In autoimmune diseases and allergies, the immune system mistakenly
perceives healthy tissue as unhealthy and launches an unnecessary attack,
leading to uncomfortable and sometimes dangerous symptoms.
This article will look at some of the main features of the immune system
and how it defends the body from pathogens and other invaders. It will also
look at problems that can arise with the immune system.
The immune system consists of
a range of components, including:
- white blood cells (leukocytes)
- the spleen
- The bone marrow
- The lymphatic system
- The Thymus
- the tonsils, adenoids, and appendix
White blood cells circulate in
the blood and lymphatic vessels, looking for pathogens. When they find one,
they begin to multiply and send signals to other cell types to do the same.
The lymphatic system forms a
network similar to the blood vessels. It carries a substance called lymph
instead of blood. Lymph is a fluid that carries immune-related cells to areas
that need them.
The body stores white blood
cells in different places, known as lymphoid organs.
These include:
- The thymus: A gland behind
the breastbone, where white blood cells known as lymphocytes mature.
- The spleen: An organ at
the upper left of the abdomen where immune cells gather and work.
- Bone marrow: Soft tissue in the centre of the bones that
produces red and white blood cells.
- Lymph nodes: These are small, bean-shaped glands throughout
the body, especially in the neck, underarms, groin, and abdomen. They link
via lymphatic vessels. Immune cells gather in lymph nodes and react when
antigens are present. This can lead to swelling.
- The tonsils, adenoids, and appendix: These are gateways for pathogens to enter the
body, so lymphoid tissue is also there.
To work effectively, the
immune system needs to be able to distinguish healthy from unhealthy cells and
tissue. It does this by recognising signals called DAMPS—danger-associated
molecular patterns.
Cell damage may be present for
many reasons, including:
- Infectious agents, such as bacteria, fungi, or viruses
- toxins, such as a bite or sting
- noninfectious physical damage, for instance, a burn
- a genetic problem within cells, as happens
with cancer
An antigen is any substance
that can spark an immune response.
In many cases, an antigen is a
bacterium, fungus, virus, toxin, or foreign body. But it can also be a cell
that is faulty or dead.
The immune system detects
pathogen-associated molecular patterns — PAMPs — in the antigen. In this way,
various parts of the system recognise the antigen as an invader and launch an
attack.
There are two main types of
leukocytes, or white blood cells:
1. Phagocytes
These cells surround and absorb pathogens and
break them down, effectively eating them.
There are several types,
including:
- Neutrophils: These are also known as granulocytes and
provide an early response to inflammation. They kill pathogens but also
die as a result.
- Macrophages: These clean up after a response. They remove
pathogens, dead neutrophils, and other debris.
- Dendritic cells: These activate the immune response and help
engulf microbes and other invaders.
- Monocytes: These can differentiate into dendritic cells and
macrophages, as needed.
- Mast cells: These trigger
an immune response when they detect an antigen.
2. Lymphocytes
Lymphocytes help the body remember and recognise previous
invaders if they return to attack again. Lymphocytes begin their life in the bone marrow. Some stay in the marrow and develop into B
lymphocytes (B cells); others travel to the thymus and become T lymphocytes (T
cells). These two cell types have different roles.
B lymphocytes produce antibodies and help alert the
T lymphocytes. T lymphocytes destroy compromised cells in the body and help to
alert other leukocytes.
Natural killer (NK) cells are also lymphocytes. NK
cells recognise and destroy cells that contain a virus.
The role of B lymphocytes
Once B lymphocytes spot the
antigen (antibody generators), they begin secreting antibodies. Antibodies are
special proteins that lock onto specific antigens.
Each B cell makes one specific antibody. For instance, one might make an antibody against
the bacteria that cause pneumonia, and
another might recognise the common cold virus. Antibodies are part of a large family of chemicals called immunoglobulins,
which play many roles in the immune response:
- Immunoglobulin G (IgG) marks microbes so that other cells
can recognise and deal with them
- IgM specialises in killing bacteria
- IgA congregates in fluids, such as tears and saliva,
where it protects gateways into the body
- IgE protects against parasites and plays a role in
allergies
- IgD stays bound to B lymphocytes, helping them start
the immune response
The role of T lymphocytes
There are distinct types of T lymphocytes
or T cells.
Helper T cells (Th cells)
coordinate the immune response. Some communicate with other cells, and some
stimulate B cells to produce more antibodies. Others attract more T cells or
cell-eating phagocytes.
Killer T cells (cytotoxic T
lymphocytes) attack other cells. They are particularly useful for fighting
viruses. They work by recognising small parts of the virus on the outside of
infected cells and destroying the infected cells.
The role of natural killer cells
Antibodies lock on to the
antigen but do not kill it — they only mark it for death. Killing other cells,
such as phagocytes, is the job of natural killer cells.
Immunity
Overall, the immune system
strengthens upon exposure to different pathogens. By adulthood, most people
have been exposed to a range of pathogens and developed more immunity.
Once the body produces an
antibody, it keeps a copy so that if the same antigen reappears, the body can
deal with it more quickly.
Some diseases, such as
measles, can be severe if they occur, which is why experts recommend vaccination. If a person
has the measles vaccine, they are unlikely to get the disease.
If an unvaccinated person has
measles once, it is also rare to get it again. In both
cases, the body stores a measles antibody. The antibody is ready to destroy the
virus next time it appears. This is called immunity.
There are three types of
immunity in humans:
- innate
- adaptive
- passive
Innate immunity
People are born with some
level of immunity that will attack invaders from day one.
This innate immunity includes the external barriers of our body — the first
line of defence against pathogens, such as the skin and mucous
membranes of the throat and gut.
This response is general and
nonspecific.
If pathogens manage to bypass
the innate immune system, macrophages will attack them. Macrophages will also
produce substances called cytokines, which increase the inflammatory response.
Adaptive (acquired) immunity
A person’s protection from
pathogens develops as they go through life.
Thanks to vaccinations and
exposure to various diseases, the body develops a range of antibodies to
different pathogens. Doctors sometimes refer to this as immunological memory
because the immune system remembers previous enemies.
Passive immunity
This is a temporary type of
immunity that derives from another
person.
For instance, a newborn
receives antibodies from the mother through the placenta before delivery and in
breast milk following delivery.
This passive immunity protects
the infant from some infections during their early life.
Immunisations change the body
in some way so it can respond effectively to various diseases.
The most common method is to
introduce antigens or weakened pathogens into a person so the individual
produces antibodies and does not become sick.
Because the body saves copies
of the antibodies, it has protection if the threat should reappear later in
life.
There are many ways in which
the immune system can go wrong. Types of immune disorders fall into three
categories:
Immunodeficiencies
These arise when one or more
parts of the immune system do not function.
They can result from:
- a condition that a person is born with, known as
primary immunodeficiency
- developments over time, for instance, older age
- a disease that affects the immune system, such
as HIV, malnutrition, obesity, or high alcohol
use
- medical treatment, such as chemotherapy, drugs to
treat an autoimmune condition, or medications to stop the body from
rejecting a transplant
These conditions can increase a person’s risk of
becoming sick or experiencing severe symptoms, as the COVID-19 pandemic has
shown.
What are examples of immunodeficiency
disorders?
Autoimmunity
In autoimmune conditions, the
immune system attacks healthy cells rather than pathogens or faulty cells. It
is unable to distinguish between healthy and unhealthy cells and tissue.
This usually occurs in one part of the body, such as the pancreas. The
destruction of pancreatic beta cells means the body cannot produce insulin,
which is how type 1 diabetes happens.
Other autoimmune diseases include:
- celiac disease
- rheumatoid
arthritis
- Graves’ disease
Hypersensitivity
With hypersensitivity, the immune system reacts exaggeratedly or
inappropriately. It attacks everyday substances, such as dust, as if they were
pathogens.
This happens with:
- asthma
- Food allergies and sensitivities
- atopic eczema
A severe reaction can lead
to anaphylactic shock, where the body
responds to an allergen so strongly that it can be life-threatening.
FAQ
Here are some answers to
questions people often ask about immunity.
How can I improve my immunity?
Tips for boosting immunity
include:
- exercising regularly
- Getting enough sleep
- Maintaining a suitable body weight
- limiting the intake of added salts, fats,
sugars, and alcohol
- Adding probiotics and prebiotics to the diet
- following a varied diet that favours fresh fruit and vegetables,
whole foods, and lean protein
- avoiding smoking
What types of immunity are there?
Innate immunity refers to the defences
people are born with, including the skin, mucous membranes, and various
components of the immune system.
Acquired immunity comes from
vaccines and exposure to diseases. These enable the body to develop antigens
that can help it fight the same disease a second time.
Passive immunity is protection
that comes from another person, for example, when a newborn is temporarily
immune to certain diseases because their mother has immunity.
Why is immunity important?
Immunity protects the body
from bacteria, viruses, and other pathogens that could lead to life-threatening
diseases.
Summary
The immune system is a complex
system that is vital for survival. When the body faces harmful invaders, such
as a virus or a splinter in the finger, it launches an attack to destroy the
pathogens.
People are born with some
types of immunity, but exposure to diseases and vaccinations can also help
boost the body’s defences.
Some people have a weakened immune system because of a health
issue or medication use. A doctor can advise on how to protect a person’s
health when living with a weakened immune system.
Ways of boosting immunity
include dietary and exercise choices, avoiding alcohol and smoking, and having
appropriate vaccinations.
xxxxxxxxxxxxxxxxxx
Comments
Post a Comment