Basic concepts in clinical immunology: A review

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