Human health and disease

Table of Contents

The Article covers Topics- Immunology, Immunity, Types of Immunity Active and Passive Immunity, Autoimmune Disease, Allergic Reaction, Innate Immunity and Acquire Immunity, Active and Passive Immunity, Structure of Antibody, Types of Antibodies, Antigens,

What is Immunology?

Study of immune system of the body is known as immunology

Who is the Father of Immunology?

Father of immunology is Edward Jenner 

What is Immune System?

The system which protect the body against harmful pathogens 

Immune system composed of lymphoid organs, tissues cells and specialised chemicals like Antibodies

Definition of Immunity:

It is the ability of the body to protect the body against for infection causing organism like bacteria virus or any toxic products which enter the body 

Immunity is also known as disease resistance 

Types of immunity: 

There are two kinds of immunity namely innate and acquired immunity

Innate immunity is also called non-specific on natural while acquired immunity is also called as active or the specific immunity

Innate immunity(Natural or Non-Specific Immunity):

It is inherited by organism from the parent and protect it is present from the birth it lacks a specific immune response for specific pathogen

This consists of four types of barrier namely, physical, physiological, cellular and cytokines barrier.

1-Physical Barrier:

It include skin and mucous membrane

(a) Skin:

As we know that skin is the largest organ of the body. Unbroken skin is the main barrier which prevent entry of microorganisms it is totally impermeable for pathogen.

It also has a population of harmless microorganism which interfere the growth of harmful microbes.

(b) Mucus:

Mucus membrane of the Epithelium lining of Respiratory, Gastrointestinal tract and Urogenital tract, secretes mucus which help in trapping of microbes entering the body.

2-Physiological Barrier:

It includes following components

(a) HCl (hydrochloric acid) secretion in the stomach, which kill the pathogens enter the body along with the food.

(b) Bile of the gallbladder 

(c) Saliva in the mouth contains Lysozyme enzyme which breaks down the Bacterial membrane.

(d) Tears from the eye also contain Lysozyme.

(e) Wax secretion of Ears trap the pathogens enter in Ears.

(f) Sweat secretion from sweat gland (present in the Skin). 

All these are preventing the microbial entry and their growth inside the body

3-Cellular Barrier:

It includes leukocytes which is the type of WBC such as-

(a) PMNL (Polymorph Nuclear Leucocytes or Neutrophils):

These cells formed from the stem cells of bone marrow. It is about 40 to 75% of blood WBC. During infection their number may increase tenfold. They reach at the site of infection and destroy the pathogen by phagocytosis.

(b) Monocytes:

It is about 2-10% of blood WBC they are motile and phagocytic in nature. The lifespan is about 10 to 20 hours 

(c) Macrophage:

Monocyte circulates in blood for about eight hours and become tenfold enlarge in size and migrate into particular tissue where are they called macrophages.

Macrophages are of two types that is Wandering type and Fixed type

Wandering type Macrophages circulated in the blood. While fixed type macrophages located inside a particular organ or tissue such as the dust cells in the lungs, kupffer cell in the liver.

(d) Natural killer cell (NK)-

It is a type of lymphocyte present in spleen and lymph nodes and bone marrow

Natural killer cell produces Perforins foreign chemicals which make pores in the plasma membrane of pathogen thereby kill the particular pathogenic target cell.

4-Cytokines Barrier:

Cytokines are small proteins produced by the T-cells and virus infected cell.

Virus infected cells cytokines usually known as Interferons which protect the non infected cells from further viral infection.

Acquired (Adaptive or Specific) Immunity:

It is develops after the birth and works against microbes and harmful molecules.

It is a specific and mediated by Antibodies or T Lymphocytes or both. They prevents from the attack of pathogens in future due to the memory B cells and T cells 

Characteristics of Acquired immunity:

Acquire immunity exhibit following characteristics-

(i) Specificity:

It has the specificity to differentiate between foreign molecules and body cells 

(ii) Diversity:

It has diversity that that is recognise Vast variety of molecules 

(iii) Discrimination:

It has the ability to discriminate between self body cells and non self foreign Cells

(iv) Memorization:

It has memorization for specific pathogen and responds with same pathogen in future infections.

What is the Specific Immune Response?

Primary and Secondary immune responses-

When the body encounters a pathogen for the first time it produces immune response called Primary immune response.

This is of low intensity and short lasting.

The next encounter with the same pathogen produces a highly intensified immune response which is long lasting.

Primary and Secondary immune responses are performed by two special types of cells present in the blood namely B lymphocyte and T lymphocytes

B-Lymphocyte produces an army of proteins which are called Antibodies or Immunoglobulins (Ig). 

Antibodies are further classified into five types namely Ig-G, Ig-M, Ig-E, Ig-D and Ig-A.

T-Lymphocyte does not produce any Antibodies but help the B cells to produce Antibodies.

Components of Acquired Immunity

There are two main components of acquired immunity that is 

1-CMI (Cell Mediated Immunity) 

2-AMI (Antibody Mediated Immunity) and it is also called Humoral Immunity (HI) 

Antibody mediated or Humoral Immunity (AMI or HI)-

The main components of the Antibody mediated Immunity are Antibodies which are produced by the modified B cells (called Effectors or Plasma B cells).

In response to Antigen or Pathogen B cells differentiate into two types of cells that is Memory B cell and Plasma or effectors B cells 

The memory B cells have a longer lifespan. It remains dormant until activated once again when same pathogen or antigen in the body infect the body.

The Effectors or Plasma B cells produces Antibodies which reacts to particular antigen.

Antibody or Immunoglobulin-

The Antibodies or Immunoglobulins are produced by modified B cells, that is Plasma or Effectors cells.

Antibodies are present in the blood plasma or at the surface of B cells.

Structure of Antibody (Monomeric Structure):

Antibodies are chemically protein molecule consists of four polypeptide chains. in which two are the smaller chains and Two are the longer chains.

The smaller ones is known as light chain(L) and the longer chains are called heavy chain(H).

All the chains are joined together by disulfide bond which form between two Sulphur containing amino acid such as Cysteine.

Polypeptide chains join in a such a manner that they are  appear to capital Y shaped structure or Gama shaped structure, hence it is also known as Gamma globulin 

Because they participate in immune response hence also called immunoglobulins (Ig).

All the four chains represented as (H2L2).

A monomeric antibody has two light chains and two heavy chains

The two arms of antibody represent the antigen binding site, which bind specifically with specific antigen.

While the stem region represent the constant area.

Types of Antibodies:

On the basis of differences in the heavy chain there are five types of antibody 

Antibody-G (Ig-G):

It is also called Gamma antibody and found in monomeric form.

It is the maternal or placental antibody because transfer from mother to developing embryo during the pregnancy through the placenta.

Antibody-A (Ig-A):

It also called Alpha Antibody. It is the Secretory antibody and present in both monomeric and dimeric form.

It is present in most of the secretion as well as in mother milk which secreted during initial days of pregnancy called colostrum.

Antibody-M (Ig-M):

It is also called mu Antibody. it is the largest antibody and Pentameric in Structure.

It is produce firstly in response of pathogen and reach first at the site of infection.

 Antibody-E (Ig-E):

It is also called it Epsilon antibody. It is present in the monomeric form.

Ig-E involve in allergic reaction hence also called allergic antibody.

 Antibody-D (Ig-D):

It is the also called delta antibody its function is not very clear but increase during infection.

Cell mediated immunity (CMI):

It is directed by T lymphocyte, which is also originated from bone marrow but mature in the thymus gland.

T cell is similar to the B cell in a structure, but functionally different.

During the immune response following types of T cells are formed which perform different function such as

(TH) Helper T cell or Inducer T cell

(TC) Cytotoxic T cell or Killer T cell

(TM) Memory T cell or Prime T cell

(TS) Suppressor T cell or Regulator T cell

The T cell bear surface T cell known as T cell receptor (TCR) which responds to specific antigen.

It plays an important role in discrimination between body cells as self and foreign particles as nonself.

CMI is also responsible for the graft rejection during the organ transplantation.

Types of acquired immunity:

There are two types of acquired immunity namely active and passive immunity.

Active immunity:

When a host is introduced to Antigen which may be in the form of living or dead microbes or other proteins the antibodies are produced in the host body this type of unity is known as active immunity. it is slow and takes time to give its full effective respond

It is further divided into two categories Artificial and Natural.

(i)Artificial active immunity:

It is the resistance induced by vaccine.

Vaccines are preparation of lived or killed microorganism or their products used for immunization.

(ii)Natural active immunity:

It is the resistance developed by the natural infection of a particular microorganisms or pathogen.

Passive immunity:

It is produced by a donor other than infected person such as an animal. It is short lived and further divided into natural and artificial.

Natural passive immunity 

It is the resistance transferred from the mother to foetus (developing baby) in the form of Ig-G antibody to the placenta before for birth.

After birth Ig-A antibody present in colostrum, which is yellowish fluid secreted by mother during the initial days of lactation

Artificial passive immunity 

It is induced by readymade antibody administration to the receiver or patient body like ATS (anti tetanus serum).

It is prepared by active immunization of horses with Antigen.

It is used for passive immunization of Tetanus

Vaccination and immunization:

The principle of immunization or vaccination is based on the property of memory of the immune system.

Vaccination is preparation of antigenic proteins or pathogen which are introduced in the body and stimulate antibody production.

The Antibody neutralize the pathogenic agent, during actual infection because vaccine generate memory B and T cells that recognise the pathogen quickly.

Antivenom in snake bite is  the injection which is given to the patient containing preformed Antibodies against the snake venom.

This is called passive immunization.

The process of introduction of vaccine into an individual provides protection against a disease is called vaccination.

Immunization is a process by which the body produces antibodies against the preventable diseases after administration of specific vaccines.

Recombinant DNA technology has allowed the production of antigenic polypeptide of pathogen in bacteria Yeast.

Such as hepatitis B vaccine (HBV) produced from Yeast.

What is the Antigen?

These are substances or pathogens and their products which when introduced into the body stimulate the production of antibodies.

Hence we can see that any substances which stimulate the production of antibodies called antigen.

Chemically they are conjugated proteins Like Glycoproteins, Nucleoproteins and Lipoproteins etc.

The components of antigens bind with the antibody called Epitopes or Antigenic determinant. Our body cells also express antigenic proteins on the plasma membrane. Antigens which present on the body cells called auto-antigen or self antigen.

if Antigen came from outside the body called Exo-antigen or Nonself antigen 

What is Allergy?

It is the hypersensitive reaction of a person to some foreign substances coming contact with foreign substances entering the body.

The substances that cause allergic reaction are called allergens. such as dust, pollen, spores, feathers, plants bacteria etc 

Symptoms of Allergy:

Symptoms include sneezing, watery eyes, running nose and the difficulty in breathing.

Mostly affected parts are mucous membrane and skin.

How body produces Allergy?

It is due to the release of chemical called Histamine, Serotonin and Antibody-E (Ig-E).

Mast cells (modified Basophil cells) secrete histamine and serotonin.

For determining cause of allergy the patient is exposed to small doses of possible allergens and then the allergic reaction studied.

How Allergy Treated:

The medicines are Antihistamine, Adrenalin and steroids are very effective in the treatment of allergy.

What is the Autoimmunity (Autoimmune disease)?

Memory based acquired immunity involve in higher vertebrate which is based on the ability to discriminate between foreign organism from self cells and bodies proteins.

If the immune system fails to recognize self from non-self, it is start destroying the body’s protein or cells and leads to autoimmune disease

This condition is called autoimmunity.

What is the Cause of Autoimmunity? 

There is no exact cause yet known for autoimmune disease.

The genetic factor and environmental factors may be responsible for the autoimmunity.

For example-Rheumatoid Arthritis

It is due to the attack of mutant Antibody (Ig-G) and Antibody (Ig-M) resulting inflammation of joints, destroying cartilage which causes pain in joints.


For part one notes click here

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