immunity

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what is immunity?

the overall ability of the host to be able to fight the disease-causing agent by the help of the immune system is called immunity.

it is of two types innate and acquired immunity.

innate immunity-

it is a non-specific type of immunity present since birth it provides a different kind of barrier for foreign agents. * non-specific means that no discrimination and memory against external agents.

1) physical barriers-skin, mucous lining our epithelium of tracts.

2) physiological barrier- acid in stomach saliva and tears

3) cellular barrier-leukocytes or WBC like polymorph nuclear leukocytes and monocytes and macrophages.

4) cytokine barrier- interferons and interleukins. *interferons are released by virus-infected cells to protect other cells.interleukins are the WBC messenger.

acquired immunity- it is a pathogen-specific type of immunity and has memory.

*primary response- a low-intensity response when the body encounters the pathogen for the first time.

secondary response- repeated encounters the same pathogen it is of higher intensity.

the immune responses are carried out with the help of two lymphocytes present in our blood

B-lymphocytes- they produce an army of a protein called antibodies which fight the pathogens.

T-lymphocytes- help the b lymphocytes with producing the antibodies.

there are 2 types of acquired immunity

1) antibody-mediated

2)cell-mediated

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all about antibodies-

-they are also called immunoglobulins. they are made up of glycoprotein and 4 polypeptide chains.

-2 smaller ones are called light chains and Bigger ones are called heavy chains. hence antibodies are represented as H2L2

different types of antibodies-

-IgG-it is a monomeric form presence is 75 percent. it is found in blood, extracellular fluid, and Rh factor

-Ig A- it has mono or dimeric form. it constitutes 15 percent. it is found in body secretions like milk

-Ig M- it has a mono or pentameric form. it constitutes 10 percent. it is found in blood, extracellular fluid, and ABO.

-Ig E- it is monomeric and constitutes less than 1 percent. present in an extracellular fluid produces an allergic response.

-Ig D-it is monomeric and constitutes percent. found in B-lymphocytes.

- these antibodies are found in blood and their response is called the humoral immune response.

the T-lymphocytes cause the cell-mediated response . which is responsible for graft rejection.

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active immunity-

it is slow and takes time to give its full effect. the host is exposed to antigens.*antigens are toxic foreign substances. which may be in the form of dead or living microbes or other proteins and then antibodies are produced in the host. Eg when injected during immunization or during natural infection.

passive immunity-

ready-made antibodies are injected in the body of the host. Eg. is mother milk secretes a yellow fluid called colostrum which has IgA. the foetus receives antibodies via the placenta.

vaccination-

the principle is based on the memory of the immune system.

in vaccination inactivated or weak antigens are introduced in the body h generate memory B and T cell which will bombard the antigen with massive production of antibodies on the second contact.

in cases like tetanus and snake bites where immediate response is needed direct antibodies or antitoxins are injected. this is passive immunization.

* hepatitis B vaccine produced from yeast.

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allergies-

it is the exaggerated response of the immune system to certain antigens present in the environment.

the antigens are called allergens. the antibodies produce are of Ig E type.

it is due to chemicals like histamine and serotonin from mast cells.

of drugs like an antihistamine, adrenalin and steroids quickly reduce symptoms of the allergy.

autoimmunity-

1) higher vertebrates can distinguish b/w foreign and self cells and molecules.

2) due to genetic and unknown reasons the body attacks self cells.

Eg rheumatoid arthritis.

the immune system in the body-