Immune System and Vaccination ( Zoology )

 

Immunity

It is the capability of multicellular organisms to resist harmful disease causing microorganisms. Our immune system gives us that ability.

It is of two types : 

Innate immunity ( inborn immunity )

It protects us by providing different types of barriers to the entry of foreign agents or any pathogen into our body.

Four types of barriers : 

Physical barriers : Skin is the main physical barrier which prevents entry of other micro-organisms into the body. Mucus coating of epithelium lining the respiratory, gastrointenstinal ( digestive tract, alimentary canal ) and urinogenital tracts also help in trapping microbes entering our body.

Physiological barriers : It includes acid in stomach, saliva in mouth, tears from eyes. Tears and saliva contains lysozyme ( an enzyme which destroys cell walls of certain bacteria ) which can destroy bacterial pathogens.

Cellular barriers : It includes WBC monocytes and natural killer cells. Natural killer cells control several types of tumors and microbial infections by limiting their spread and subsequent tissue damage.

Cytokine barriers : Virus-infected cells secretes proteins call interferons which protect non-infected cells from further viral infection. It inhibits the synthesis of proteins required for replication of virus. It controls viral diseases but do not kill the virus.

Acquired Immunity ( Adaptive immunity )

This is gained after birth and is pathogen specific ( different for different type of pathogens ). When a new pathogen enters our body, it initiate a primary response by which B and T cells ( Bone-marrow & Thymus cells ) start dividing to produce effector B and T cells for controlling disease and also memory B and T cells which are stored in the spleen and lymph nodes throughout the life. When that pathogen again enters our body the memory B and T cells start dividing and produce effector B and T cells. This is called secondary response which is effective / intensive than primary response.

Two types of acquired immunity

Humeral Immunity : Also called antibody mediated immunity. It shows a quick response against pathogens. The B lymphocytes produce an army of proteins in response to the pathogens. When pathogens enter our body, B lymphocytes get activated and differentiated to plasma cells which secrets large no of antibodies in order to fight with pathogens. Undifferentiated B-lymphocytes remain as memory cells. 

Antigens : A substance that enters the body and starts a process that can cause disease. It stimulates antibody production. So called antibody generating.

Haptens : These are small antigenic molecules which are antigenic but incapable of inducing immune response.

Antibody : An antibody is a protein produced by the body's immune system when it detects antigens. These are immunoglobulin proteins ( Ig proteins ).
The five primary classes of immunoglobulins are IgG, IgM, IgA, IgD and IgE.

Colostrum is a golden liquid ( contains IgA ) that a nursing mother expels from his breasts within 24-48 hours after delivery.

IgE is a mediator in allergic responses and parasite infections.

IgD activates and suppresses lymphocytes activity.

IgG is the only antibody that can cross placenta and provide immunity to the foetus.

IgM is the largest antibody and it has high number of antigen binding sites.

All of these antibodies are found in blood. So called humoral immune system.

Cell mediated immunity : Cell-mediated immunity is an immune response that does not involve antibodies. It ( T cells ) activates and helps in producing B cells.

Helper T cells stimulates B cells to produce antibodies and killer T cells.

Killer / Cytotoxic T cells kill infected cells when activated.

Suppressor T cells suppress the functions of helper and killer T cells so that immune system does not attack the body's own cells.

Memory T cells remain in the lymphatic tissue and recognize the pathogens even after many years of the first encounter.

Acquired immunity is also classified into two types : active immunity , passive immunity.

Active immunity : The immunity which results from the production of antibodies by the immune system in response to the presence of an antigen. Natural active immunity is acquired when antigens gain access into the body during natural infection. Artificial active immunity is the resistance induced by vaccines.

Passive immunity : It is the transfer of active humoral immunity of ready-made antibodies. Natural passive immunity is gained from the mother to his child during initial days of lactation i.e. colostrum. Anti-venom and Anti-tetanus serum are the example of Artificial passive immunity.

Disorders of immune system :  Allergy or hypersensitivity is a disorder in which a person feels hypersensitiveness because of the exaggerated response of the immune system by the introduction of allergens present in our environment.    Hay fever, Asthma, Anaphylactic shock, eczema etc.

Autoimmunity : The memory based acquired immunity always destroys the foreign antigens but never attacks the body's own protein. But sometimes due to some genetic or other reasons it attacks self cells which damages the body.

Vaccination : Vaccination is the administration of a vaccine to help the immune system develop protection from a disease. First generation vaccine is the whole organism vaccine either live, weakened or killed forms. Second generation vaccine are sub-unit vaccines consisting of defined protein antigens or re-combinant protein components. Third generation vaccines are DNA vaccines made up of a plasmid which is genetically engineered to produce one or two specific antigens.

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