Immunity, types of immunity, Active immunity, Passive immunity, Humoral immunity, Cellular immunity, Herd immunity & Immunization Agents, Immunoglobulins.

In this article, we will understand in detail about the Immunity, types of immunity, Active immunity, Passive immunity, Humoral immunity, Cellular immunity, Herd immunity & Immunization Agents, Immunoglobulins (IgG, IgA, IgM, IgE, IgD).


Immunity is the ability of an organism fight against the disease. the immune system’s way of protecting the body against an infectious disease.

Active Immunity

Active immunity: It is the individual develops immunity which an as a result of an infection or by specific immunization and is usually associated with presence of antibodies or cells having a specific action on the micro-organism concerned. with a particular infectious disease or its own toxin. It can be acquired in 3 ways: 1. Following clinical infection for examples- chicken pox, rubella and measles.

2. Following subclinical or inapparent infection, e.g., polio, diphtheria.

3. Following immunization with an antigen which may be a killed vaccine or a live attenuated vaccine.

Humoral immunity, cellular immunity and combination of above two also comes under active immunity.

Humoral Immunity

Humoral immunity: It comes from B cell which proliferates and manufactures specific antibodies after antigen presentation by macrophages. The antibodies are located in the immunoglobulin fraction of serum and are of five main types, they are IgG, IgM, IgA, IgD and IgE.

Cellular Immunity

Cellular immunity: Although antibodies are quiet effective in combating most infectious disease, humoral immunity does not cover all the situations that one finds in infectious disease. Some pathogens such as M. leprae, M. tuberculosis and S. typhi escapes the bactericidal action of leukocyte. Here the activated T cell performs phagocytic action.

Passive Immunity

Passive immunity: When antibodies produced in one body are transferred to another to induce protection against disease, it is known as passive antibodies immunity. Here the body does not produce its own antibodies but depends upon ready-made antibodies. Passive immunity can be induced: *By administration of an antibody containing preparation (immunoglobulin or antiserum). *By transfer of maternal antibodies across the placenta. Human milk also contains protective antibodies.
*By transfer of lymphocytes to induce passive cellular immunity.

Herd Immunity

Herd immunity, also known as population immunity, is the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection. Herd immunity: It is the level of resistance of a community or a group of people to a particular disease. Herd immunity is the overall resistance in a community.

Immunization Agents

Immunizing Agents: These agents can be mainly classified as vaccines, immunoglobulin, and antisera.


It is an immune biological substance, designed to produce specific protection against a given disease. It stimulates the production of protective antibodies. and other immune mechanisms.

Live Vaccine

Live vaccines: •These type of vaccines are prepared from live organisms. These organisms lost their capacity to produce a full blown disease but retain their immunogenicity.

•Live vaccines should not be administered to an individual with immunodeficiency, immune suppression, malignancy or on therapy with corticosteroids, alkylating agents, antimetabolite or on radiation. •When two live vaccines need to be administered either administer them simultaneously at two different sites or maintain a gap of four weeks between the administrations of two vaccines. •Live vaccines will achieve its immunization with a single dose, exception is polio vaccines which require three or more doses at spaced interval to produce effective immunity. •Live vaccines must be stored properly to maintain its potency.

Inactived or Killed vaccine

•Organisms killed by heat or chemicals when infected into the body stimulate immunity. They are usually safe but are less effective than live vaccines.

•In most cases these kinds of vaccines require a booster dose.

•The duration of immunity following killed vaccines vary from months to many years. The only absolute contraindication against killed vaccines are severe general or local
reaction to the previous dose.

Toxoid Vaccines

•Certain organisms. produce exotoxins (diphtheria, tetanus). The toxins produced by these organisms are detoxified and used in the preparation of vaccines.

Cellular Fractions

In certain instances, vaccines are prepared from extracted cellular fractions. For examples: meningococcal, pneumococcal.

Combination Vaccines

If more than one immunizing agent is included in a single vaccine they are called as combination vaccines. The aim of combination vaccine is to simplify administration, reduce cost and minimize the number of contact of patients with health system. For example: DT, DPT, Pentavalent vaccine, MMR etc.


The human immunoglobulin system composed of major five immunoglobulins, IgA, IgD, IgG, IgM & IgE. •IgG: Major immunoglobulin in serum. It consists of 85% of total serum immunoglobulin. It is the only immunoglobulin which can cross the placenta.

•IgM: Accounts for 10% serum immunoglobulin. It represents the antibody that promptly formed with exposure to antigen. Its presence may be indicative of recent infection. IgM is the macro immunoglobulin. Immune response of killed vaccine is relatively poor in comparison to live vaccines.

•Killed vaccines are safer than live vaccines.

•Adjuvants required in killed vaccine. •IgA: About 15% of total serum immunoglobulin.
It is found relatively in larger quantities in body secretions.

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By GS India Nursing Academy!!

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