There’s a battle going on beneth the skin, Thousands of microbes crawl in the body in a daily invasion. Yet we rarely notice because an army of B cells, T cells, natural killer cells, and other parts of your immune system counterattack, ripping most microbes to pieces.

Those that survive gives a runny nose, cough, and feverish feeling, and on rare occasions, more serious illness.

The immune system fights against bacteria, viruses, and pollen and venom from bees.

Anything foreign that enters our body is surrounded and either neutralized or destroyed by our immune system before it can cause damage to your body.

What Is Immunity?

An immune system is an organism’s protection from invading organisms and foreign substances, such as bacteria, viruses, fungi, helminths, protozoa, pollen, transplanted tissues, and insect venom.

These substances are called antigens.

Immunity is a specific defensive response of a host when a foreign substance or organism invades it.

The body reacts to the foreign substance (antigen) by forming antibodies. Antibodies are proteins that are made by the body in response to an antigen.

An antigen causes the organism to form antibodies and specialized lymphocytes that target the specific antigen. If the antigen invades again, these antibodies and specialized lymphocytes attack the antigen, making the antigen inactive or destroyed. This is called an immune response against an antigen.

Types of Immunity

In general, there are two types of immunity: innate and adaptive.


  • When microbes attack our bodies, we defend ourselves by utilizing our various mechanisms of immunity.
  • Innate immunity refers to defenses that are present at birth.
  • They are always present and available to provide rapid responses to protect us against disease.
  • Innate immunity does not involve specific recognition of a microbe.
  • Innate immunity does not have a memory response, that is, a more rapid and stronger immune reaction.
  • Components of innate immunity are the first line of defense (skin and mucous membranes) and the second line of defense (natural killer cells and phagocytes, inflammation, fever, and antimicrobial substances).
  • Innate immune responses represent immunity’s early-warning system and are designed to prevent microbes from getting into the body.


The development of antibodies and specialized lymphocytes is called acquired immunity

Acquired immunity is the protective defense mechanism an organism develops against foreign substances and microorganisms. This type of immunity is established throughout an individual’s life.

There are two types of acquired immunity. These are active and passive.

Active immunity:

Naturally acquired active immunity occurs when an individual is exposed to an infectious disease. The individual’s immune system responds by making its own antibodies and lymphocytes (T cells and B cells) on its own.

Artificially acquired active immunity occurs when an individual is given a vaccine. A vaccine is a substance that contains the weakened or dead organisms. These antigens stimulate the immune response, but do not cause major sickness. The body remembers the antigen with memory cells the next time there is exposure to the antigen.

Passive immunity:

In passive immunity, already-made antibodies are introduced or passed on to an individual. The individual does not make its own antibodies.

Artificially acquired passive immunity occurs when antibodies are developed outside the individual and intravenously injected into the body. This form of immunity helps the body’s own defenses in combating infection.

Naturally acquired passive immunity occurs when antibodies (IgG) are made by a mother and passed on to the fetus through the placenta. IgA antibodies are also passed to the baby in the first secretion of breast milk, called colostrum, during breast-feeding.

Serum and Antibodies

Serum is the fluid that remains after the blood has clotted and the serum is separated from the blood cells and clotted material.

Electrophoresis is a laboratory technique that introduces electrical current into a serum placed in a gel. This causes proteins within the serum to move across the gel at different rates, which represents different globulins.

There are three globulins. These are called alpha, beta, and gamma globulins. Gamma globulin contains the most antibodies. A serum rich in antibodies is called either gamma globulin or serum globulin.

Gamma globulin can be taken from a person who is immune to an antigen and injected into a person who lacks the antigen, who then immediately becomes immune from the antigen.


Antibody-mediated immunity, which is also known as humoral immunity, uses antibodies in extracellular fluids, such as mucus secretions, blood plasma, and lymph, to fight with antigens.

These antibodies, produced from B cells, which are also known as B lymphocytes, attack bacteria, bacterial toxins, and
viruses that invade body fluids. sometimes, They also attack transplanted tissues.

Antibody-mediated immunity was discovered by German scientist Emil von Behring at the turn of the twentieth century  to create an immunization against diphtheria.


Cell-mediated immunity involves specialized lymphocytes called T cells, also known as T lymphocytes, to attack foreign organisms rather than using antibodies.

T cells are also effective against helminths, fungi, and protozoa.

Cell-mediated immunity was explained by Russian biologist, Elie Metchnikoff, who in the early 1900’s noticed that phagocytic cells were much more effective in animals that were immunized.

This immunity was used in the mid-twentieth century to protect people against tuberculosis.




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