Innate immunity is the body’s natural inborn resistance to infection and it is quick in responding to invasive microbes. It is a component of the immune system that is an inherited protective mechanism, and which protect the body of an animals from many kinds of pathogens. Innate immunity is a nonspecific immune response to antigens, and it is the first line of defense that is not acquired through prior contact with an infectious disease or pathogen. This form of immunity is not directed at any specific organism or antigen, instead they are intended for all pathogens or foreign substances to which the body is exposed. The response of the innate immune system to pathogen is static (i.e. it does not improve with repeated exposure to antigens and there is no immunological memory on subsequent exposures), and subsequent exposure of the body to antigens does not change or increase the level of response of this type of immunity. Innate immunity is comprised of four (4) types of defensive barriers which help to keep away pathogenic microorganisms from the host body, and these are:
- Anatomic barriers such as the skin, epithelium, gastrointestinal tract (GIT), mucous membrane, mammary gland (breast), respiratory tract, and urinogenital tract.
- Physiologic barriers such as body temperature, pH level, chemical mediators (e.g. cytokines, lysozyme, antimicrobial peptides, interleukins, surfactants, lipids, enzymes, interferon, and complements).
- Phagocytic barriers which include special forms of the white blood cells (e.g. monocytes, neutrophils, and eosinophils) which internalize/engulf and digest or breakdown foreign substances including whole microorganisms that enter the body.
- An inflammatory barrier which occurs following tissue damage and it is usually characterized by redness, swelling (oedema), pain and heat. In this type of innate immunity, vascular fluids containing protective serum proteins and phagocytic cells are released to the site of infection to stop the spread of the infection.
- Intact normal microflora: Normal microflora are populations of microorganisms (normally bacteria and fungi) which inhabit the internal and external body of healthy individuals. They are either resident or transient on the body, and they play a major role in protecting the body from foreign substances by antagonizing the colonization of body surfaces by pathogenic microorganisms. Normal microflora play a major role of microbial antagonism, and when they are not present or disturbed, pathogens colonize, proliferate and cause disease. The human body is in constant association with microorganisms (both beneficial and harmful organisms), and it is the job of microflora to ensure that harmful organisms do not colonize it. Normal microflora also outcompete microbes for essential nutrients in the body.
In healthy individuals, most of the microorganisms encountered by the body of a human host are readily cleared and eliminated by the mechanisms of the innate (nonspecific) immune system even before they activate the adaptive immune response to the invading foreign substance. Innate immune response is very vital as the first line of defense against an infection because it provide the very primary defense during the critical stage of infection (i.e. at the onset of host exposure to an antigen) since the adaptive (specific) immune response takes some time to come up.
However, there are some hosts factors that can affect and cause variations in the response of innate immunity based on individual differences such as: age, sex, nutrition, host genetic determinants, stress, hormonal activity, and fatigue. Some diseases or infections that occur in humans are sex-specific. Malnutrition also predisposes the body to infection because undernourishment affects the immune system and weakens its ability to protect the body from foreign substances or immunogens. Newborns and the elderly are more prone to some infections due to the low level of their immune system which is either still developing (as in infants) or is in a declining stage (as in old people). Stress, fatigue, hormonal imbalance and the genetic makeup of individuals are other predisposing factors that may affect the level of response of the immune system of a human host due to differences in their physiological and environmental conditions.
Abbas A.K, Lichtman A.H and Pillai S (2010). Cellular and Molecular Immunology. Sixth edition. Saunders Elsevier Inc, USA.
Actor J (2014). Introductory Immunology. First edition. Academic Press, USA.
Alberts B, Bray D, Johnson A, Lewis J, Raff M, Roberts K and Walter P (1998). Essential Cell Biology: An Introduction to the Molecular Biology of the Cell. Third edition. Garland Publishing Inc., New York.
Bach F and Sachs D (1987). Transplantation immunology. N. Engl. J. Med. 317(8):402-409.
Barrett J.T (1998). Microbiology and Immunology Concepts. Philadelphia, PA: Lippincott-Raven Publishers. USA.
Jaypal V (2007). Fundamentals of Medical Immunology. First edition. Jaypee Brothers Medical Publishers (P) Ltd, New Delhi, India.
John T.J and Samuel R (2000). Herd Immunity and Herd Effect: New Insights and Definitions. European Journal of Epidemiology, 16:601-606.
Levinson W (2010). Review of Medical Microbiology and Immunology. Twelfth edition. The McGraw-Hill Companies, USA.
Roitt I, Brostoff J and Male D (2001). Immunology. Sixth edition. Harcourt Publishers Limited, Spain.
Zon LI (1995). Developmental biology of hematopoiesis. Blood, 86(8): 2876–91.