● When a host is exposed to `color{Violet}"antigens"`, which may be in the form of `color{Violet}"living or dead microbes"` or other `color{Violet}"proteins"`, `color{brown}"antibodies"` are produced in the host body.

● This type of immunity is called `color{Violet}"active immunity"`.

● `color{Brown}"Active immunity"` is `color{Violet}"slow"` and takes `color{Violet}"time"` to give its full effective response.

● Injecting the microbes deliberately during `color{Violet}"immunisation"` or `color{Violet}"infectious organisms"` gaining access into body during natural infection induce `color{Violet}"active immunity"`.

● When `color{Violet}"ready-made antibodies"` are directly given to protect the body against foreign agents, it is called `color{Brown}"passive immunity"`.

● `color{Violet}"Mother’s milk"` is considered very essential for the `color{Violet}"newborn infant"`

● This is due the `color{Violet}"yellowish fluid"` `color{Brown}"colostrum"` secreted by mother during the initial days of lactation has abundant `color{Violet}"antibodies (IgA)"` to protect the infant.

● The `color{Violet}"foetus"` also receives some antibodies from their mother, through the `color{Violet}"placenta during pregnancy"`.

● These are some examples of `color{Violet}"passive immunity"`.

● The `color{Violet}"principle"` of `color{Brown}"immunisation or vaccination"` is based on the property of `color{Violet}"memory"` of the immune system.

● In `color{Violet}"vaccination"`, a preparation of `color{Violet}"antigenic proteins"` of pathogen or `color{Violet}"inactivated/weakened pathogen"` (`color{Brown}"vaccine"`) are introduced into the body.

● The `color{Violet}"antibodies"` produced in the body against these antigens would `color{Violet}"neutralise"` the `color{Violet}"pathogenic agents"` during actual infection.

● The vaccines also generate `color{Violet}"memory"` – B and T-cells that recognise the pathogen quickly on `color{Violet}"subsequent exposure"` and overwhelm the invaders with a massive production of antibodies.



● If a person is infected with some `color{Violet}"deadly microbes"` to which quick immune response is required as in `color{Violet}"tetanus"`, we need to directly inject the `color{Violet}"preformed antibodies"`, or `color{Brown}"antitoxin"` (a preparation containing antibodies to the toxin).

● Even in cases of `color{Violet}"snakebites"`, the injection which is given to the patients, contain `color{Violet}"preformed antibodies"` against the `color{Violet}"snake venom"`.

● This type of immunisation is called `color{Brown}"passive immunisation"`.

● `color{Violet}"Recombinant DNA technology"` has allowed the production of `color{Violet}"antigenic polypeptides"` of pathogen in bacteria or yeast.

● Vaccines produced using this approach allow `color{Violet}"large scale production"` and hence greater availability for immunisation, e.g., `color{Violet}"hepatitis B vaccine"` produced from `color{Violet}"yeast"`.

● When some people go to a `color{Violet}"new place"` and suddenly start `color{Violet}"sneezing, wheezing"` for no explained reason, and when they leave the place, their `color{Violet}"symptoms dissappeared"`.

● It is because those people are `color{Violet}"sensitive to some particles"` in the environment.

● The above-mentioned reaction could be because of `color{Violet}"allergy"` to `color{Violet}"pollen, mites"`, etc., which are different in different places.

● The `color{Violet}"exaggerated response"` of the immune system to certain `color{Violet}"antigens"` present in the environment is called `color{Brown}"allergy"`.

● The `color{Violet}"substances"` to which such an `color{Violet}"immune response"` is produced are called `color{Brown}"allergens"`.

● The antibodies produced to these are of `color{Violet}"IgE type"`.

● Common examples of allergens are `color{Violet}"mites in dust"`,`color{Violet}" pollens"`, `color{Violet}"animal dander"`, etc.



● Symptoms of allergic reactions include `color{Violet}"sneezing"`, `color{Violet}"watery eyes"`, `color{Violet}"running nose"` and `color{Violet}"difficulty in breathing"`.

● Allergy is due to the release of chemicals like `color{Violet}"histamine and serotonin"` from the `color{Violet}"mast cells"`.

● For determining the cause of allergy, the patient is exposed to or injected with `color{Violet}"very small doses"` of possible `color{Violet}"allergens"`, and the reactions studied.

● The use of drugs like `color{Violet}"anti-histamine"`, `color{Violet}"adrenaline"` and `color{Violet}"steroids"` quickly reduce the symptoms of allergy.

● Somehow, `color{Violet}"modern-day life style"` has resulted in `color{Violet}"lowering of immunity"` and more sensitivity to `color{Violet}"allergens"` – more and more children in metro cities of India suffer from `color{Violet}"allergies and asthma"` due to sensitivity to the environment.

● This could be because of the `color{Violet}"protected environment"` provided early in life.