Abstract
Immunity is the state of protection against foreign pathogens or substances(antigens). Host defence mechanisms consist of innate immunity (natural immunity), which mediates the initial protection against infections, and adaptive immunity (specific/acquired immunity), which develops more slowly and provides more specialized and more effective defence against infections. The immune system evolved to protect multicellular organisms against pathogens. The body is protected against pathogens by a variety of effector cells and molecules that together make up the immune system. All the cellular elements of blood, including the red blood cells, platelets and white blood cells of the immune system, ultimately derive from the hematopoietic stem cells of the bone marrow. The cells of the adaptive immune system consist of lymphocytes, antigen-presenting cells and effector cells that eliminate microbes. Strategies of avoidance, and tolerance represent different ways of dealing with pathogens. Anatomic barriers and chemical barriers e.g complement and antimicrobial proteins may be considered as primary forms of avoidance.Macrophages,neutrophils and dendritic cells are important cells that that detect infection. Pattern recognition receptors (PRRs) recognize simple molecules and regular patterns of molecular structures called pathogen associated molecular patterns. Some PRR are transmembrane proteins e.g Toll like receptors (TLRs). Vaccination is a simple, safe, and effective way of protecting people against harmful diseases, before they come into contact with them. Immunization is the process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine. Inappropriate immune responses can result into hypersensitivity, autoimmune disease or immune deficiency.
Highlights
Jenner's bold experiment was successful, it took almost two centuries for smallpox vaccination to become universal, an advance that enabled the World Health Organization to announce in 1979 that smallpox had been eradicated arguably the greatest triumph of modern medicine [1]
That not all adaptive immune responses entail the production of antibodies, and the term antigen is used in a broader sense to describe any substance that can be recognized by the adaptive immune system
After the T and B lymphocytes have matured in the thymus and bone marrow, they travel to the lymph nodes and spleen where they remain until the immune system is activated
Summary
An adaptive immune response confers lifelong protective immunity to reinfection with the same pathogen This distinguishes such responses from innate immunity, which, at the time that von Behring and Kitasato discovered antibodies, was known through the work of the great Russian immunologist Elie Metchnikoff. Metchnikoff discovered that many microorganisms could be engulfed and digested by phagocytic cells, which he called macrophages These cells are immediately available to combat a wide range of pathogens without requiring prior exposure and are a key component of the innate immune system. That not all adaptive immune responses entail the production of antibodies, and the term antigen is used in a broader sense to describe any substance that can be recognized by the adaptive immune system Both innate immunity and adaptive immune responses depend upon the activities of white blood cells, or leukocytes. The main focus of this review will be on the diverse mechanisms of innate &adaptive immunity
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