Introduction to Immunity:

Immunity is a biological word which explains a state of having adequate biological defenses to avoid disease, infection or other unwanted biological invasion. Immunity comprises both specific and non-specific components. The non-specific components act either as barriers or as eliminators of a broad range of pathogens irrespective of the antigenic specificity. Other components of the immune system adapt themselves to each and every new disease encountered and are capable to produce pathogen-specific immunity.

Concept of Immunity:

The theory of immunity has intrigued mankind for thousands of years. The primitive view of disease was that it was caused via supernatural forces and that illness was a form of theurgic punishment for evil thoughts visited on the soul by the gods or by one's enemies. Between the time of Hippocrates and the nineteenth century, when the base of the scientific process were laid, diseases were attributed to the alteration or imbalance in one of the four humors. The modern term 'immunity' derives from the Latin immunis, signifying exclusion from military service, tax payments or other public services. The first written explanations of the concept of immunity might have been made by the Athenian Thucydides who, in 430 BC, explained that if the plague hit Athens 'the sick and the dying were tended through the pitying care of those who had recovered, as they knew the course of the disease and were themselves free from the apprehensions. For no one was ever attacked a second time, or not by a fatal outcome'. The word 'immunes', is as well found in the epic poem 'Pharsalia' written around 60 B.C. by the poet Marcus Annaeus Lucanus to explain a North African tribe's resistance to the snake venom. 

The first clinical explanation of immunity that arose from a particular disease causing organism is possibly Kitab fi al-jadari wa-al-hasbah (A Treatise on Smallpox and, translated 1848) written through the Islamic physician Al-Razi in the ninth century. In dissertation, Al Razi explains the clinical presentation of smallpox and measles and goes on to point out that that exposure to such particular agents confers lasting immunity. Though, it was with Louis Pasteur's Germ theory of disease that the fledgling science of immunology starts to describe how bacteria caused disease, and how, following infection, the human body gained the capability to resist the further infections. 

The birth of active immunotherapy might have started with Mithridates VI of Pontus. To induce the active immunity for snake venom, he recommended by employing a process identical to modern toxoid serum therapy, by drinking the blood of animals that fed on venomous snakes.

According to Jean de Maleissye, Mithridates supposed that animals feeding on venomous snakes acquired a few detoxifying property in their bodies and their blood should have attenuated or transformed components of the snake venom. The action of such components may be strengthening the body to defy the venom rather than exerting toxic effect. Mithridates reasoned that, via drinking the blood of such animals, he could acquire identical resistance to the snake venom as the animals feeding on the snakes. Likewise, he sought to harden himself against poison, and took daily sub-lethal doses to build tolerance. Mithridates are as well states to have fashioned a 'universal antidote' to protect him from all the earthly poisons. For almost 2000 years, poisons were thought to be the proximate cause of disease and a complex mixture of ingredients, termed as Mithridate, was employed to cure poisoning all through the Renaissance.

A revised version of this cure, Theriacum Andromachi, was employed well into the 19th century. In the year 1888 Emile Roux and Alexandre Yersin isolated diphtheria toxin, and following the year 1890 discovery by Behring and Kitasato of antitoxin based immunity to diphtheria and tetanus, the antitoxin became the primary main success of modern therapeutic Immunology. 

Passive Immunity:

Passive immunity is basically the form of immunity which takes place when antibodies are transferred from one person to the other individual or when antibodies of animal origin are introduced to the human. This kind of immunity is short acting and is generally seen in cases where a patient requires immediate protection from something and he or she can't form antibodies fast adequate independently.

Naturally acquired passive immunity:

In the natural passive immunity, antibodies are passed from a mother to the child. Antibodies can be transferred via the placenta, or transmitted via the colostrums, a liquid that is generated in the breasts for a baby's very first meal. The antibodies transmitted via the colostrums and placenta usually only last for some weeks, which is long adequate to let the baby to begin to build up its own immune system and to prepare its own antibodies.

Artificially acquired passive immunity:

Artificial passive immunity comprises the introduction of antibodies via means like injection. For illustration in the treatment of several diseases, patients might be given a serum derived from the patients who have recovered to assist them fight the disease. This practice is at times seen if people are dealing with an outbreak of a new or very virulent disease for which no known treatment is accessible.

Passive transfer of cell-mediated immunity:

Passive or 'adoptive transfer' of cell-mediated immunity, is granted by the transfer of 'sensitized' or activated T-cells from one individual to the other. It is seldom utilized in humans as it needs histocompatible donors, which are frequently hard to find out. In unmatched donors this kind of transfer carries some risks of graft versus host disease. It has, though, been employed to treat some diseases comprising several kinds of cancer and immunodeficiency. This kind of transfer distinct from a bone marrow transplant, in which the hematopoietic stem cells are transferred.

Active Immunity:  

The Active immunity is a scientific word employed to explain the procedure via which a being, usually a human or an animal, builds up a specific resistance to the harmful substance. There are generally two manners this can occur. First is natural exposure, such as when a person catches a cold or encounters specific bacteria in the environment. Vaccinations can as well cause an active immune response via artificial means. In either of the case the immune system of body makes a targeted response to the injurious substance by first recognizing it and then building up antibodies against it, both of which allow the body to fight it off in the future.

Innate Immunity:

Naturally acquired active immunity takes place if a person is exposed to a live pathogen and builds up a primary immune response that leads to immunological memory. This kind of immunity is 'natural' as it is not induced through deliberate exposure. Most of the disorders of immune system function like immunodeficiency and immuno-suppression can influence the formation of the active immunity.  

Artificially acquired active immunity:

Artificially acquired active immunity can be persuaded through a vaccine; a substance which includes antigen. A vaccine stimulates a primary response against an antigen devoid of causing symptoms of the disease. The word vaccination was coined by Edward Jenner and adapted through Louis Pasteur for his pioneering work in the vaccination. The process Pasteur employed entailed treating the infectious agents for such diseases so they lost the capability to cause the serious disease. Pasteur adopted the name vaccine as a generic word in honor of Jenner's discovery that Pasteur's work built on.

Innate Immunity: 

The innate immunity system is what we are born by and it is non-specific; the entire antigens are attacked pretty much uniformly. It is genetically based and we surpass it on to our offspring.

 Surface Barriers or Mucosal Immunity:

a) The first and possibly, most significant barrier is the skin. The skin can't be penetrated by most of the organisms except it already has an opening, like a scratch or cut.

b) Mechanically, pathogens are drive out from the lungs by ciliary action as the tiny hairs move in an upward motion; coughing and sneezing suddenly eject both living and non-living things from the respiratory system; the flushing action of saliva, tears and urine as well force out pathogens, as does the sloughing off of skin.

c) Sticky mucus in the respiratory and gastrointestinal tracts entraps most of the microorganisms.

d) Acid pH (< 7.0) of skin secretions restrains bacterial growth. Hair follicles secrete sebum which includes lactic acid and fatty acids both of which slow down the growth of some pathogenic bacteria and fungi. Areas of the skin not covered by hair, like the palms and soles of the feet, are most vulnerable to the fungal infections.

e) Tears, saliva, nasal secretions and perspiration include Lysosome, an enzyme which destroys Gram positive bacterial cell walls causing the cell lysis. Vaginal secretions are as well slightly acidic (that is, after the onset of menses). Spermine and zinc in semen destroy a few pathogens. Lactoperoxidase is a powerful enzyme found in the milk of mother.

f) The stomach is a formidable obstacle insofar as its mucosa secrete hydrochloric acid (0.9 < pH < 3.0, much acidic) and protein-digesting enzymes which kill numerous pathogens. The stomach can even destroy drugs and various chemicals.

Acquired Immunity:

The acquired immunity is one in which a defense or immunity, to a disease is obtained via the course of the life of an organism. This signifies that if the life of organisms began, it had no natural immunity to the condition. Acquired immunity might be the outcome of a number of various factors, comprising vaccinations, prior exposure or even immunity passed down from the mother prior to a baby is born.

Acquired immunity takes time to build up after first exposure to a latest antigen. Though subsequently, the antigen is remembered and succeeding responses to that antigen are faster and more efficient than those which occurred after the first exposure.

The white blood cells which are mainly responsible for acquired immunity are:

• Lymphocytes (T cells and B cells)

Usually, an acquired immune response starts if antibodies, generated by B cells (B lymphocytes), encounter an antigen.

The other participants in acquired immunity are as follows:

• Dendritic cells
• Cytokines
• The complement system (that improves the efficiency of antibodies)

Cell-mediated immunity:

This kind of immunity in living organisms is similar to a defense method that protects their body from injurious infection causing attacks of bacteria, virus and fungi. The most significant role in immunization is played through white blood cells or lymphocytes that are generally produced in the bone marrow and are then transported to different organs for their protection. Cell mediated immunity is as well a part of this entire defense system.

Humoral immunity:

Humoral immunity is a way through which the body protects itself from the infection by generating antibodies which target foreign material in the bloodstream which is seen as potentially dangerous, marking it for annihilation. It is a portion of the adaptive immune system that is activated in response to a particular threat, as opposed to the innate immune system that is constantly active however less efficient. Another part of the adaptive system is cellular, or cell-mediated, immunity, in which cells discharge toxins to kill invaders or attack them directly, devoid of the involvement of antibodies. Altogether, humoral and cellular immunity are designed to protect the body against a broad variety of threats which could compromise it.

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