Immune system

بسم الله الرحمن الرحيم
السلام عليكم ورحمة الله وبركاته

Immune system

An immune system
is a system of biological structures and processes
within an organism that protects against disease
by identifying and killing pathogens and tumor cells.
It detects a wide variety of agents,
from viruses to parasitic worms,
and needs to distinguish them from the
organism's own healthy cells and tissues in order
to function properly.
Detection is complicated as pathogens can evolve rapidly,
producing adaptations that avoid the immune system
and allow the pathogens to successfully infect their hosts.

To survive this challenge,
multiple mechanisms evolved that recognize and
neutralize pathogens.
Even simple unicellular organisms such as bacteria
possess enzyme systems that protect against viral infections.
Other basic immune mechanisms evolved in ancient eukaryotes
and remain in their modern descendants,
such as plants and insects.

These mechanisms include antimicrobial peptides
called defensins, phagocytosis,
and the complement system.
Jawed vertebrates, including humans,
have even more sophisticated defense mechanisms.
The typical vertebrate immune system consists
of many types of proteins, cells, organs,
and tissues that interact in an elaborate
and dynamic network.
As part of this more complex immune response,
the human immune system adapts over time
to recognize specific pathogens more efficiently.
This adaptation process is referred to as
"adaptive immunity" or "acquired immunity" and
creates immunological memory.

Immunological memory
, created from a primary response to a specific
pathogen provides an enhanced response
to secondary encounters with that same
specific pathogen.
This process of acquired immunity is the
basis of vaccination.
Primary response can take 2 days and
up to 2 weeks to develop.
After the body gains immunity towards
a certain pathogen,
when infection by that pathogen occurs again,
the immune response is called the secondary response.

Disorders in the immune system can result in disease,
including autoimmune diseases,
inflammatory diseases and cancer.
Immunodeficiency diseases occur when
the immune system is less active than normal,
resulting in recurring and life-threatening infections.
Immunodeficiency can either be the result
of a genetic disease,
such as severe combined immunodeficiency,
or be produced by pharmaceuticals or an infection,
such as the acquired immune deficiency
syndrome (AIDS) that is caused by the retrovirus HIV.
In contrast, autoimmune diseases result from
a hyperactive immune system attacking normal tissues
as if they were foreign organisms.
Common autoimmune diseases include
Hashimoto's thyroiditis, rheumatoid arthritis,
diabetes mellitus type 1, and lupus erythematosus.
Immunology covers the study of all aspects
of the immune system,
having significant relevance to health and diseases.
Further investigation in this field is expected to play
a serious role in promotion of health
and treatment of diseases.