Human immune system explained

Immunity

Immunity can be defined as the defensive mechanism of the body that acts against foreign proteins, toxins produced by the invading pathogens or microorganisms and micro organisms.Natural immunity can be defined as the immunity that is present since birth in a human to any of the pathogens, microbial proteins and toxins. We resist many of the diseases by our own immune system and need no external vaccine or drug for the resistance. This is so because we have the necessary antibodies for resisting such diseases.

Types of immunity found in humans

Immunity can be either generated inside the body or the body can also acquire the immunity from outside sources.

Active Immunity

Active acquired immunity is the immunity which we acquire later in life when we are exposed to some pathogen. When the body successfully resists an attack from the below given factors, then active acquired immunity is attained. The immunity provided by the T cells and B cells are types of active immunity. The factors are:

A particular microorganism

A closely similar micro organism

A modified toxin

A killed microorganism

A micro organism that has been artificially made less hostile

Artificially acquired active immunity

A vaccine can induce artificially acquired immunity. Vaccine contains the necessary antigen due to which the body creates specific vaccine for resisting a particular pathogen.

Passive immunity

If we inject the serum of any animal that has antitoxins (produced because as a result of active immunity) into a human being, then the antitoxins produce passive immunity for that particular organism inside the human being.

Artificially acquired passive immunity

There are some antibodies that the human body cannot produce. When these antibodies are directly injected through short term immunization vaccines, the body attains passive immunity for those diseases of which antibodies have been injected.

Naturally acquired passive immunity

This immunity is developed in the body during pregnancy when some antibodies are directly passed form the maternal blood to the fetal blood.

Terms of immunity for familiarization

Antigen

The foreign bodies, proteins or bacteria that enter into the blood are called antigens. An antigen’s body can divided into 2 parts viz. hapten and protein nucleus. Hapten can be a mono or a polysaccharide.
Antibody

When an antigen enters the body, the body reacts to this invasion by secreting antibodies or immune bodies. These antibodies are part of the plasma proteins and are classified under the gamma globulin fraction of plasma proteins. The antibodies can be classified in 4 groups. These 4 groups are given below.

Antitoxins- These are released when toxic substances enter inside the body.

Agglutinins- These antibodies clump together the antigens and then destroy them.

Precipitins- They cause the precipitation of foreign proteins.

Haemolysins or cytolysins- They cause the haemolysis of old RBC’s.

MALT

The abbreviation malt stands for mucosa associated lymphoid tissue. Some parts of the human body like skin, eye,  salivary glands, lung , breast, thyroid and gastrointestinal tract contain MALT which is diffuse system containing small amounts of lymphoid tissue. MALT contains high amounts of B cells, macrophages, plasma cells and T cells. These immunity cells resist and destroy the antigens that pass through the mucosal lining.

GALT

GALT stands for gut associated lymphoid tissue. GALT is found in esophagus, tonsils, adenoids stomach and other areas of the gut. GALT also contains T and B cells which resist and destroy pathogens.

Similarly, other areas of the body also have lymphoid tissues that contain numerous T and B cells for resisting attack of pathogens/antigens. These are:

BALT or bronchus associated lymphoid tissue,

NALT or nasal associated lymphoid tissue,

CALT or conjuctival associated lymphoid tissue,

LALT or larynx associated lymphoid tissue, and

MALT or mucosa related lymphoid tissues are found in the body.

Mechanism of human immune system

The human body has a 3 layer immune defense mechanism against the foreign pathogens and toxins. The primary layer is called the physical barrier, the secondary layer is called the innate human system and the tertiary barrier is the adaptive immune system.

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