Everyday we are exposed to large number of infectious agents. However, only a few of these exposures result in disease Immunology is a branch of biology that covers the study of immune systems in all organisms.
The fact that the body is able to defend itself from most of these foreign agents. This overall ability of the host to fight the disease-causing organisms, conferred by the immune system is called immunity. Immunity is of two types: (i) Innate immunity and (ii) Acquired immunity.
Innate immunity is non-specific type of defence, that is present at the time of birth. Innate immunity consist of four types of barriers. These are —
(i) Physical barriers : Skin on our body is the main barrier which prevents entry of the micro-organisms. Mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts also help in trapping microbes entering our body.
(ii) Physiological barriers : Acid in the stomach, saliva in the mouth, tears from eyes–all prevent microbial growth
(iii) Cellular barriers : Certain types of leukocytes (WBC), of our body like polymorpho-nuclear leukocytes (PMNL-neutrophils) and monocytes and natural killer (type of lymphocytes) in the blood.
(iv) Cytokine barriers : Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.
Acquired (adaptive) Immunity
Acquired immunity, on the other hand, is pathogen specific. It is characterised by memory. This means that our body when it encounters a pathogen for the first time produces a response called primary response which is of low intensity. The same pathogen elicits a highly intensified secondary or anamnestic response. This is ascribed to the fact that our body appears to have memory of the first encounter.
The primary and secondary immune responses are carried out with the help of two special types of lymphocytes present in our blood, i.e., B-lymphocytes and Tlymphocytes.The B-lymphocytes produce an army of proteins in response to pathogens into our blood to fight with them. These proteins are called antibodies.
Each antibody molecule has four peptide chains, two small called light chains and two longer called heavy chains.
Different types of antibodies are produced in our body. IgA, IgM, IgE, IgG are some of them.Because these antibodies are found in the blood, the response is also called as humoral immune response. This is one of the two types of our acquired immune response – antibody mediated. The second type is called cell-mediated immune response or cell-mediated immunity (CMI)
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