Types of Immunity and Antibodies | Additional Study Material for NEET PDF Download
Complementary System :
It is formed by complementary component or C-component and they are inactive but when agglutination occurs in our body they become active and show inflammation, cell lysis and promote phagocytosis. Complement system takes part in both innate and acquired immunity.
Acquired Immunity : It is the resistance that an individual acquires during life. This is generated in response to an exposure to the micro-organism in question.
This type of immunity is founds only in vertebrates.
It is also called Adaptive or specific immunity
This immunity is acquired after birth through experience.
This immunity recognizes and selectively eliminates the pathogen.
Features of Acquired immunity :
(i) Specificity : Acquried immunity is specific for specific micro-organisms.
(ii) Diversity : This system recognizes the vast variety of micro-organisms.
(iii) Discrimination between self and non-self. It can recognize self (body or tissue) and non self (foreign tissue) and respond according to them.
(iv) Memory : When a pathogen enters inside the body, body takes longer time to recognize and respond to it. This is called primary immune response but the memory of this encounter remains in immune system.
When this pathogen enters second time inside the body, body's immune system rapidly recognizes this pathogen and respond quickly to it. This is called secondary immune response. This is based on memory of immune system.
Types of Acquired Immunity :
(i) Active acquired immunity :- Resistance developed by an individual as a result an antigenic stimulus.
(a) Natural :- Results from a clinical or inapparents infection by a microorganism.
(b) Artificial :- Resistances induced by vaccine
Vaccines :-Preparation of live or killed microorganism or their products used for immunization.
(ii) Passive Immunity :- It is received passively by host without participation or contribution from host's immune system. Immunological memory is absent here and the readymade antibodies are given in immuno suppressive individual. This is called passive immunity.
(a) Natural :- Resistance passively transferred from mother to baby. Mother milk gives passive immunity to the new born child by colostrum (first mother milk) →Ig A type of antibody.
(b) Artificial :- Resistance passively transferred to a recipient by administration of antibodies.
Examples : human immunological administration.
Anti - tetanus serum (ATS), Anti - rabies serum (ARS), Anti - diptheria serum (ADS)
Difference between active and passive immunity
| Active immunity | Passive immunity |
1. | Produced actively by the immune system of host | Received passively by the host and the host' s immune system does not participate. |
2. | Induced by infection or by contacts with immunogen, e.g. vaccines. | Conferred by introduction of ready-made antibodies. |
3. | Immune response-durable and effective | Immune response-short lived and less effective. |
4. | Immunity develops only after a lag period | Immunity effective immediately. |
5. | Immunological memory present. Subsequent challenge with booster dose more effective. | No immunological memory. Subsequent administration of antibody less effective due to "immune elimination: |
6. | Serves no purpose in immuno deficient host. | Applicable in immunodeficient host |
7. | Used for prophylaxis to increase body resistance. | Used for treatment of acute infection. |
Active Immunity : This immunity develops after infection or vaccination.
Active immunity is formed by lymphocytes, lymphocytes are produce in bone marrow (Haematopoisis).
After production some of lymphocytes migrates from bone marrow to thymus cells and mature as T-cells (Thymus cell).
Lymphocyte which remain in bone marrow mature as B - cells (Bone marrow cells) so, bone marrow and thymus gland are primary lymphoid organ.
After maturation some lymphocytes migrate from bone marrow & thymus gland to the spleen & lymph nodes like tonsils, and proliferate ( 
in no.) Here, so spleen, lymph nodes, tonsils and peyer's patches [mucosal associated lymphoid tissue (MALT)] are called secondary lymphoid organs.
Based on these two type of lymphocytes there are two types of active immune system.
(1) C.M.I.S. → Cell mediated immune system or Cellular immunity This immune system is based on T-cells. (60-70%) There are 4 type of T-cell
(i) Helper T-cell
(ii) Killer T-cell or cytotoxic T-cell
(iii) Supressive T-cell
(iv) Memory T-cell When pathogens enter inside the body first macrophage interact with them and activates TH-cell by releasing cytokines or ILs or monokines.
(i) Helper T-cell → This activated helper cell stimulates the killer T-cell and B-cell and these killer & B-cell start dividing and produce clone (group of similar cells) this phenomenon is called clonal selection.
They produce lymphokines (messenger molecules) which cause accumulating of WBCs to the affected site.
TH-cells also stimulate B–cells to produce antibodies and facilitate the action of other T–cells.
(ii) Killer T-cell : These cell or clone of these cell destroy the infected cells or target cell and kill the pathogen and also the cancerous cells by secreting Lymphotoxic substances and secrete lymphokines which attracts phagocytes.
These are responsible for cell–mediated immunity. They also destroy transplanted, tumour cells and other foreign cells.
(iii) Suppressor Cells (TS) :- These suppress the functions of TC and TH cells. B–cells and plasma cells are also affected by TS cells by synthesizing suppressor factors and suppress the entire immune system for attacking the own body
(iv) Memory T-cell : They don't kill the pathogen or don't form the antibodies but these cell retain the memory of every encounter.
They convert into effector cells (TC) on later encounter with specific antigen even after several years.
(v) Antigen Presenting Cells :- In immune mechanism every antigen molecule is processed by antigen presenting cells like macrophages, B-lymphocytes etc. This processed antigen is presented on the surface of these cells.
When a T- helper lymphocyte passes closely by the side of the antigen presenting a cell bearing the antigen on its surface, it recognizes the antigen and becomes activated. Now T-helper cells activate the B-cells and T-killer cells.
These cells in turn develop clones by frequent divisions in themselves.
(2) A.M.I.S. (Antibody mediated immune system or humoral immunity)
This immune system is based on B-lymphocyte (10-20%) and these B-lymphocyte secret the antibody.
Antibody or Immunoglobulin : These are complex glycoprotein molecule made up of 4 polypeptide chains - two light and two heavy chains.
These two chains are held together by disulphide bond in shape of Y molecule.
Two top tips of this molecule bind with antigen [large and complex foreign molecules mainly proteins that activate the specific immunity] like lock and key fashion and make antigen-antibody complex.
Function of Antibodies :
(i) Agglutination : Antibody attach with the antigen which is present on the surface of pathogen and destroy the pathogen by cell lysis.
(ii) Opsonisation : Coating of bacteria (Ag) with opsonin Antibody (IgG and IgM) facilitates the phagocyte cells and these antibodies or opsonin promote phagocytosis by combination with antigen.
(iii) Neutralization : Antibodies neutralize the toxin of bacteria by attaching with them.
TYPE OF ANTIBODIES –
Various Types of Immunoglobulins in Human
S.No. | Group of Antibodies | Total Quantity (%) | Main Characters and occurrence | Functions |
1. | IgA | 10 | The primary antibodies present in colostrum, M.W. 1,70,000 : present in saliva, mucus and other secretions. | Protection of mucous membranes and outer surface of body and protection from inhaled ingested pathogens. |
2. | IgD | 1-3 | Present in trace amount on the surface of lymphocytes in blood, M.W 1,85,000 | Activation of B-lymphhocytes and development and maturation of immune reactions. |
3. | IgE | 0.05 | Present in very small quantities, show specific linkage with mast cells and basophils, M.W. 1,88,000 | Stimulation of mast cells, related to allergic reactions and protection from parasites. |
4. | IgG | 75-80 | Most abundantly found antibodies main immunoglobulin of blood and interstitial fluid which has capacity to pass through placenta, M.W. 1,46,000 (lightest) | To stimulate the complementary system, to provide immune power to human embryo and specific linkage with phagocytic cells for phagocytosis. |
5. | IgM | 5-10 | Oldest and first antibody generated in response to antigens, present in blood plasma (80% ) and interstitial fluids and large sized immunoglobulin with pentameric form, M.W. 9,60,000 (heaviest) | First appeared antibody generated at the time of defence, strong agglutination, related to complement system. |
Mostly intra-vascular
IgG – Protects body fluids.
IgA – Protects body surfaces.
IgM– Protects body blood stream.
IgE – Mediates regional hypersensitivity.
IgD – Activation of B-lymphocyte
- First line of Defence : Skin, Mucous membrane
- Second line of Defence : Neutrophils, Monocytes, Macrophage, interferon, fever.
- Third line of Defence : Specific immunity by T- and B-lymphocytes
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