“The ability of human body to resist almost all types of micro-organisms, their toxins if any, foreign cells & abnormal cells of the body is termed as “Immunity”
“The study of functioning & disorders of Immune system is termed as “Immunology”.
Immunity is conferred to animals through the activities of the Immune System, which combats infectious agents.
“Immune System is a collection of cells & proteins that work to protect the body from potentially harmful, infectious micro-organisms”
MAIN FUNCTIONS OF IMMUNE SYSTEM
Protection of body from all types of micro organisms & toxins that tend to damage the tissues and organs of body.
Immune system also play important role in:
- Control of cancer
- Rejection problems when organs or tissues are transplanted.
Immune system can be divided into two functional divisions:
1. Innate Immunity System
2. Acquired Immunity System
“The NON SPECIFIC type of immunity which result from general processes , rather than from processes directed at specific disease organism (Such as antigen –antibody reaction) is called. INNATE OR NATURAL IMMUNITY & the system which is responsible for this type of immunity is called Innate IMMUNITY System.
TYPES OF BARRIERS PROVIDED BY INNATE IMMUNITY SYSTEM
This system provides two types of barriers:
- MUCOUS MEMBRANE & etc.
- Gastric juice (Acidic secretion of stomach) & etc.
Skin, Mucous membrane & their secretions act as “First line of Defence”
The intact skin provides an impenetrable barrier to the vast majority of infectious agents.
2. MUCOUS MEMBRANES
Most of the micro-organisms can enter only through the mucous membranes that lines the digestive, respiratory & urogenital tracts. However these areas are protected by movements of mucous & secretions (e.g Lysozyme in tears) to destroy many microbs.
3. ACIDIC SECRETIONS
Most of he microorganisms present in food or trapped in swallowed mucus from the upper respiratory tracts are destroyed by highly acidic gastric juice of stomach.
SECOND LINE OF DEFENSE
If some how micro-organisms are able to penetrate the outer layer of the skin or mucous membrance, they encounter a second line of Defence offered by Innate Immunity system.
It is non specific & comprises of
2. ANTIMICROBIAL PROTEINS
3. INFLAMMATORY RESPONSE
Phagocytes are certain type of WBC’S which can injest internalize & destroy the particles including infectious agents.
EXAMPLES OF PHAGOCYTIC CELLS
Neutrophils (Polymorphonuclear Neutrophiles are short lived phagocytic cells which can ingest the bacteria or any foreign matter very actively.
MACROPHAGES (BIG EATERS)
The other phagocytic cells, the MONOCYTE can develop into large LONG-LIVED MACRO PHAGES when they reside in various tissues of body. ALSO CALLED AS ANTIGEN PRESENTING CELLS.
Macrophages not only destroy individual micro organisms but also play a crucial rule in further immune response by “Presenting” parts of that microorganisms to other cells of immune system. For this reason, they are termed as “ANTIGEN PRESENTING CELLS.
NATURAL KILLER (NK ) CELLS
Natural killer cells (NK Cells ) are the large lymphocytes, which destroy the
- Virally infected own cells of the body
- Foreign cells
- Abnormal cells (cancerous cells)
NK cells do not phagocytize the target cells, instead, they bind to their target cells, release some PORE FORMING PROTEINS (PERFORINS), that literally punch large round holes in the membrane of attacked cells & eventually cause lysis of the target cells. This kind of destroying the target cells is called “CYTOTOXICITY”
2. ANTIMICROBIAL PROTEINS
- Important antimicrobial proteins are:
- Compliment proteins
Lysozyme, is a mucolytic polysaccharide that causes the LYSIS OF BACTERIA it is present in TEARS, SALIVA, & MUCUS SECRETION.
Complement is a collective terms that describes a system of about 20 PROTEINS, many of which are INACTIVE ENZYME PRECURSORS. The principal actors in this system are 11 Proteins. All these proteins are present among the Plasma Proteins.
ACTIVATION OF COMPLIMENT PROTEINS
These proteins can be activated by two ways.
- CLASSICAL PATH WAY-Act in Adaptive Immunity system.
- ALTERNATIVE PATH WAY- Act in Innate Immunity System.
Main functions of compliment proteins are as follows:
1. DIRECT LYSIS OF BACTERIA
2. PROMOTE THE PHAGOCYTOSIS OF BACTERIA
3. NEUTRILIZATION OF VIRUSES
4. CHEMOATTRACTANTS FOR MACROPHAGES.
INTERFERONS (ANTIVIRAL AGENTS)
Interferon are secreted by virally infected cells or some lymphocytes to induce a state of ANTI VIRAL RESISTANCE in unaffected tissues of the body.
Inflammation is the body’s reaction to an injury or by entry of micro organisms.
EFFECTS OF INFLAMMATION
A cascade of chemical reactions take place during inflammatory response.
1. When injured, BASOPHILS and MAST CELLS release a substance called HISTAMINE which causes.
- Increased permeability of adjacent capillaries.
- Local vasodilatation
- Increased leakage of capillaries.
Redness, heat, swelling, pain in injured tissue.
FEVER -(ALSO CONTRIBUTES TO DEFENSE OF BODY)
In case of warm blooded animals, a no. of micro organisms who escape away from inflammatory response to infect some large part of the body, trigger FEVER. It is usually caused by WBC’S, that release the substance called as PYROGEN.
- High fever is dangerous but moderate fever contributes to the defense of the body.
- It inhibits the growth of micro-organisms.
- May speed up the repair of damaged tissues.
- Facilitates the phagocytosis, increase the production of interferons.
“The specific type of Immunity which does not develop until after the body is first attacked by a bacterial disease or a toxin, is called “Adaptive or Acquired Immunity”. The system which provides this type of immunity is called “ADAPTIVE or ACQUIRED IMMUNE SYSTEM”
“Acquired Immunity is provided by special Immune System that form Antibodies & activated lymphocytes that attack & destroy the specific organisms or toxins. This is the THIRD LINE OF DEFENCE.
DEVELOPMENT OF IMMUNE SYSTEM (LYMPHOCYTES ARE THE BASIS OF ADAPTIVE IMMUNE SYSTEM)
Acquired Immune system is actually the product of body’s Lymphocytic system. The responses of adaptive Immune system is provided by Lymphocytes.
TYPES OF LYMPHOCYTES
During fetal development, all lymphocytes come from Bone Marrow. But depending upon their migration & maturity, they can be divided into two populations.
1. “T” – Cells or “T” LYMPHOCYTES
2. “B” – Cells or “B” LYMPHOCYTES.
1. “T” LYMPHOCYTES
“The lymphocytes that are destined to eventually form ACTIVATED “T” LYMPOCYTES first migrate to & then mature in THYMUS GLAND, that is why, they are called as “T” LYMPHOCYTES”
These are responsible for “CELL-MEDIATED IMMUNITY
2. “B” LYMPHOCYTES
“The lymphocytes that are destined to form ANTIBODIES are processed first in the LIVER (before birth) & then in BONE MARROW (after the birth). This population of cells was first discovered in birds where processing occurs in BURSA OF FABRICIUS (not found in mammals), hence they are called as “B” LYMPHOCYTES.”
These are responsible for HUMORAL IMMUNITY
ADAPTIVE IMMUNE SYSTEM IS INITIATED BY ANTIGENS
In order to develop a specific immune response, the immune system must recognize the invading organisms and / or foreign proteins from its self tissues & proteins.
Any foreign substance, that elicit the immune response is called antigen. In general Antigens are proteins or large polysaccharides.
RESPONSE OF IMMUNE SYSTEM TO ANTIGEN
The immune system responds to an antigen by ACTIVATING LYMPHOCYTES & PRODUCING ANTIBODIES (Soluble Proteins). The antibody combines with antigen & helps to eliminate it from the body.
BASIC TYPES OF ADAPTIVE IMMUNITY
The adaptive immune system mounts two types of attacks on invading micro-organisms.
1. HUMORAL IMMUNITY
2. CELL MEDIATED IMMUNITY (CMI)
1. HUMORAL IMMUNITY
“The immunity which is mediated by circulating antibodies produced by B-lymphocytes is called “ HUMORAL IMMUNITY”.
MAJOR FUCTIONS OF HUMORAL IMMUNITY
Humoral Immunity provides major defence against “BACTERIAL INFECTIONS
MECHANISM OF ACTION OF B CELLS
“B” CELL RECEPTORS
Each B-cell has specific type of antibodies on its cell surface. This antibody serves as ANTIGENIC RECEPTOR.
ACTIVATION OF SPECIFIC “B” CELLS
On entry of foreign antigen, those B cells specific for that antigen enlarge immediately, becomes activated & form two types of cells:
1. PLASMA CELLS
2. MEMORY CELLS
1. PLASMA CELLS
The activated B-cells proliferate rapidly & transform into enlarged effectors cells called plasma cells.
Plasma cells secrete ANTIBODIES into the circulation that help to eliminate that particular antigen.
ACTIONS OF ANTIBODIES.
After the formation of antigen-antibody complex antibody can inactivate the invading agent in one of the several ways.
- By activation of complement system that cause the Lysis.
- Direct Phagocytosis.
- Neutralization of the toxins released by bacteria.
- Agglutination of microorganism.
Some of the activated B-cells don’t go on to form the plasma cells but instead, form moderate number of new B-cells, which don’t secrete antibodies such cells are called as Memory cells.
The memory cells play important role in future immunity to this specific organism in case of re-infection.
2. CELL MEDIATED IMMUNITY (CMI)
The second type of acquired immunity is achieved through the formation of large number of Activated LYMPHOCYTES. This is called cell mediated or T-cell immunity.
FUNCTIONS OF CMI
- CMI is responsible for delayed allergic reactions & rejection of transplantation of foreign tissue.
- It provides major defence against infections due to VIRUSES, FUNGI, TUBERCLE BACILLI & some parasites.
- It also provides defence against TUMOUR CELLS.
T-CELL RECEPTORS (TCRS)
Antigens bind with specific RECEPTOR MOLECULES on the surface of T-Cells, in the same way that they bind the antibodies.
ACTIVATION OF SPECIFIC “T” CELLS.
On exposure to proper antigen, the “T” cells of specific type proliferate & release large no. of activated T-Cells.
SEVERAL TYPES OF “T” CELLS
Different types of T cells are classified into four major groups.
1. HELPER “T” CELLS
2. CYTOTOXIC “T” CELLS
3. SUPRESSER “T” CELLS
4. MEMORY “T” CELLS
1. HELPER “T” CELLS
Helper T cells are the MAJOR REGULATOR of all the immune functions.
Helper T cell receptors actually recognize a combination of antigen fragment & one of the body’s own self marker called. “MAJOR HISTO-COMPATIBILITY” (MHC) CLASS II molecules on the surface of macrophages or B cells.
Helper T-cells secrete the LYMPHOKINES which stimulate the production of both CYTOTOXIC & SUPRESSER TOXINS.
2. CYTOTOXIC “T” CELLS (KILLER CELLS)
Receptors on the surface of cytotoxic ‘T” cells recognize a combination of antigen fragment & self surface marker molecules called MHC CLASS I , found on every nucleated cells of its own body.
They are especially lethal to virally infected cells. They also destroy the cancer cells, heart transplant cells & other foreign cells.
3. SUPRESSOR “T” CELLS
Along with helper cells, In supressor, T-cells are classified as Regulatory T-Cells
After the conquerence of infection, they seems to shut off the immune response in both B-cells & cytotoxic T-cells.
4. MEMORY “T” CELLS
During CMI response, some T-cells turn into MEMORY CELLS
Memory cells protect the body in case of reaction in future.
TYPES OF IMMUNE RESPONSE
The immune system has also the ability to memorize the antigen it has encountered. Thus upon subsequent exposure to the same pathogen responds in two different ways.
1. Primary Immune Response
2. Secondary Immune Response
1. PRIMARY IMMUNE RESPONSE
The first exposure to an antigen to the immune system elicits formation of clones of effectors cells to develop specific immunity with in 5 to 10 days. This response of immune system is termed as Primary Immune response.
- DELAYED APPEARANCE
- WEAK POTENCY
- SHORT LIFE
Subsequent exposure of same antigen causes a much more rapid & much more potent antibody response. This is called Secondary Immune response. It develops to it max. with in 3-5 days.
- Rapid & quicker appearance
- Far more potent
- Longer duration (form antibodies for many months rather than for only a few weeks.)
The quicker secondary response is made possible due to ability called “Immunological Memory” of the immune system. It is based upon the long lasting memory cells produced with short lived effectors cells of pri immune response. The development of memory cells may provide life long protection against some diseases like chicken pox.
ACTIVE & PASSIVE IMMUNITY
The immunity which is acquired by own immune response is called active immunity
FUNCTION OF ACTIVE IMMUNITY
Active immunity due to development of immunological memory provide LONG TERM PROTECTION, even in some diseases (e.g in chicken Pox ) life long protection is provided.
TYPES OF ACTIVE IMMUNITY
There are two types.
1. Natural active immunity
2. Artificial active Immunity
1. NATURAL ACTIVE IMMUNITY
When the active immunity is acquired as a consequence of natural infection then it is called Natural active immunity”
2. ARTIFICIAL ACTIVE IMMUNITY
Active immunity can be acquired artificially by vaccination. In this case it is said to be “ARTIFICIAL ACTIVE IMMUNITY”
Temporary immunity which is achieved in a person without injecting an antigen, by transferring the antibodies, activated T-cells or both obtain from another person or even an animal, is called passive immunity.
FUNCTIONS OF PASSIVE IMMUNITY
Although, acquired passive immunity is short lived (last for 2-3 weeks), it boosts the immune response of the victim several folds.
TYPES OF PASSIVE IMMUNITY
There are 2 Types:
1. Natural passive Immunity
2. Artificial passive Immunity
1. NATURAL PASSIVE IMMUNITY
When antibodies are transferred from one person to another of the same species during natural processes, then such immunity is called Natural passive immunity.
A pregnant woman passes some of the antibodies to her fetus through placenta. The first breast feeding, the colostrum, of mother pass certain antibodies to her newly born infant.
2. ARTIFICIAL PASSIVE IMMUNITY
PASSIVE IMMUNITY can also be transferred artificially by introducing antibodies derived from animals or human being who are already actively immunized to that disease. This is called artificial passive immunity.
RABIES is treated in man by injecting antibodies derided from persons who have been already vaccinated against rabies. This confers the rapid immunity to combat the rapidly progressing rabies in new victim.
The process of inducing immunity as a preventive measure against certain infectious diseases is called immunization.
ADVANTAGES OF IMMUNIZATION
The incidence of number of diseases (e.g Diptheria, Measles) has declined dramatically since the introduction of effective immunization programmes. Some dread full diseases (e.g. Tuberclosis) is now under control.