Updated: Jul 30, 2020
Immunity: The term immunity is defined as resistance shown by the host (living body) against any foreign antigen including microorganisms. This resistance is a major factor in prevention of infectious disease. There are two type of immunity: (i) innate immunity and (ii) acquired immunity (I) Innate (inherent) immunity: It is by the virtue of his/her genetic and constitutional make-up and it is the resistance against microorganisms which an individual possesses by birth. Types of innate immunity (a) Species immunity – This type of immunity is referred to the resistance to pathogens shown by all members of particular species e.g. Bacillus anthracis infects human but not chicken. (b) Racial immunity – Within one species different races may exhibit differences in susceptibility (sensitivity, vulnerability) or resistance to infections. E.g. American negroes are more susceptible than white races to tuberculosis. (c) Individual immunity – Susceptibility to infection varies with different individuals of the same races and species, this is known as individual immunity. Factors influencing innate immunity are: Nutrition, Age, Hormones. (II) Acquired immunity: The resistance acquired by an individual during life is known as acquired immunity. Types of acquired immunity: Active and Passive. (a) Active immunity – Active immunity we develop after being exposed to an infection or by getting a vaccine. Active immunity is further divided into two types (i) natural and (ii) artificial. (i) Natural immunity – Antibodies made after exposure to an infection the most recent example of active- natural immunity is by covid-19, the person who recovered from corona viral develop an antibody against this virus.. (ii) Artificial immunity – this type of immunity is induced by vaccination example – we are very keenly waiting covid-19 vaccine. (b) Passive immunity develops after you receive antibodies from someone or somewhere else. This type of immunity is short-lived, because it doesn’t cause your immune system to recognize the pathogen in the future. There are two main types of passive immunity: (i) Natural (Maternal antibodies) are antibodies that transfer from a mother to child. This usually happens across the placenta or through breast milk, especially in the first few days after birth. (ii) Artificial (immunoglobulin treatments) Convalescent plasma therapy is a very suitable example of this type of immunity. (III) Miscellaneous: (i) Combined immunization (ii) Adoptive Immunization (iii) Local Immunity (iv) Herd Immunity (i) A combination of active and passive immunization is employed simultaneously which is known as combined immunization. (ii) Adoptive immunity – Injection of immunologically competent lymphocytes is known as adoptive immunity. (iii) Local Immunity – Natural infection or live viral vaccine administered orally or intra-nasally provides local immunity. (iv) Herd immunity – It refers to the overall resistance in a community. When herd immunity is low chances of epidemic increase on introduction of pathogens.