Immune system -"THE BODY GUARD" with powerful "ARSENAL" PART 1

Hello everyone ,

I love explaining about my knowledge in Biology because i am medical student :) & this is my first post related to science.Hope you will have a feel that you learned something today :) .

so lets get started ,

Introduction :-

Every day we are exposed to a large number of infection agents . However only a few of them results in diseases .why ? It is due to the fact that the body is able to defend itself from most of them . The overall ability of an individual to fight against the disease causing organisms is called Immunity.

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• The network of organ cells & proteins that protect the body from harmful infection agents such as Bacteria,Viruses,Animal parasites,Fungi etc., is called the Immune system.
• The basic requirement of the immune system is to differentiate between self and non self & to protect the body from Harmful foreign substances,Micro-organisms,Toxins & Malignant cells etc.,

Concepts of Immunology :-

Study of Immune system is called Immunology

To understand Immunology better,we have to know certain basic concepts such as lines of defence,Cells,Organs & Soluble mediators of the immune system , antigens , types of immunity , mechanism of immunity & Immunological Disorders .

lines of defence in body :-

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• First line of defence :

Whenever bacteria , viruses , Fungi and parasites try to enter the body of an organism , skin , mucous membranes & the Enzyme Lysozyme of saliva , tears etc., present their body .

• Second line of defence :-

If the microorganisms cross 1st line of defence & enter the body ,the phagocytes,Natural killer cells,Antimicrobial substances, inflammation, fever etc.,

• Third line of defence :-

If the microbes cross even the 2nd line of defence , then the lymphocytes & antibodies fight against them . It is highly specific but takes several days to become fully functional.

If all the Three lines of Defence fail, it results in diseases.

Cells of the immune system :-

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There are three types :-

1. Lymphocytes :-

These are the chief cells of the immune system ,which are of 3 types

• B-cells
• T-cells
• Larger Granular Lymphocytes (LGLs)

Based on the size , lymphocytes can also be divided into small & large Lymphocytes .Small Lymphocytes include B-cells & T-cells whereas the large lymphocytes include granular lymphocytes that consists of Natural killer cells(Nk-cells).

B-cells :-

• The lymphocytes capable of producing antibodies and can capture circulating antigens are called B-cells.
• They are produced by the "Stem cells" in the bone marrows of Adult mammals & Bursa of Fabricius in Birds.
  
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  Mature B-cells synthesize various types of antibodies which are displayed on their Membrane surface . Also called as Immuno-competent B-cells.These mature Immuno-competent B-cells reach the secondary Lymphoid organs & develop into Functional Immune cells which later differentiate into "Long Lived " memory cells & Effector plasma cells .Plasma cells produce antibodies specific to the antigen to which they are exposed .Memory cells store information about the specific antigens & Show quick response when the same type of antigen invades the body again .

T-cells :-

The lymphocytes that are not capable of producing antibodies & cannot recognize the free/ circulating antigens are called T-cells .

• They are produced in the bone marrow reach the Thymus gland & differentiate into mature T-cells .
  
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Do you know ?

Through T-cells cannot recognize the free or circulating antigens , they can recognize antigens if presented by Antigen presenting cells(Apcs) or altered self cells by MHC molecules.APCs include dendritic cells , macrophages & B-lymphocytes .

Soluble mediators of Immunity :-

There are three types namely :

• Complement proteins

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These are a group of Inactive Plasma proteins & cell surface proteins.When activated they form a Membrane attack complex (MAC) that forms pores in the plasma membrane of the affected cells allowing ECF to enter the cells & make them Sell & Burst . Some of them form a coat on the surface of the pathogens & attract Neutrophils & Macrophages to phagocytes & them destroy them.

• Cytokines

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They are small,soluble Molecules secreted mostly by the Th cells or infected cells .They bid to cell surface receptors & initiate activation or differentiation of the cell of the immune system to stimulate Phagocytosis & cyclosis of the infected cells .

Antibodies ( Immunoglobins ):-

Whenever Pathogens enter our body , the B-cells produce an army of proteins called antibodies to fight with them .

• They are Highly specialized for binding with specific antigens.
• The part of an antibody that recognizes an antigen is called Paratope(Antigen binding site).

Based on this mobility,antibodies are of two types :

• Circulating (or)Free antibody
• Surface Antibody

The circulating are present in the body fluids whereas the surface antibodies are present on the surface of the mature B-cells as well as memory cells .

Structure of Antibody

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The basic structure of an Antibody was proposed by "Rodney Porter". It is a 4-shaped molecule with 4 polypeptide chains of which two are long identical heavy chains (H) & two are small identical light chains(l).
Hence antibody is represented as H2L3... the two chains are linked by disulphide bonds .

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Antibodies can come in different varieties known as isotypes .There are five antibody isotypes known as IgA, IgD, IgE, IgG, and IgM , each named with an "Ig" as prefix stands for immunoglobulin .

References :

• Cells of Immune system

• Immunology

• Antibodies

• Soluble mediators in Immunity

• Lines of defence

• Antigen presenting cells

• Structure of Antibody

• Lymphocytes