![]() ![]() Examples include the complement system, interferons and interleukin-1. Chemical defenses consist of proteins able to interact directly or indirectly with invaders, activating cascades of reactions to cause inflammation and recruit further immune mediators that help to defend the body.Physical and chemical barriers protect the body from invasion and include things like the skin and eyelashes, while substances at these barriers, such as tears, mucous, blood clotting factors and stomach acid help to stop and destroy them.In humans, the innate immune system encompasses physical and chemical barriers, that provide a first line of defense, and chemical (humoral) and cellular aspects as the second line of defense. The innate immune response is fast acting and non-specific, meaning it does not respond differently based on the specific invader that it detects. It is considered the more evolutionarily primitive immune system and consequently, as well as being found in vertebrates, is also found in various shapes and forms in plants, fungi and insects. This type of immunity is written in one’s genes, offering lifelong protection. Innate immunity, also known as genetic or natural immunity, is immunity that an organism is born with. Anything that triggers the immune system is called an antigen. Anything that does not posses these “self tags” may be recognized by the immune system as foreign and targeted. In humans, all nucleated cells express distinctive surface molecules called major histocompatibility complex class I (MHC class I) that identify them as being self. ![]() How does the immune system tell self from non-self? Immunity is defined as an organism’s ability to protect itself from anything that it does not recognize as self, such as a pathogen or toxin. In this article, we explore both aspects of the immune response, how they come about, the key cells and molecules involved and their role in protecting us. The immune system delivers this protection via numerous pathways, but this can broadly be broken down into two arms, innate immunity and adaptive immunity. Organisms must constantly protect themselves from harm caused by invaders such as bacterial and viral pathogens. ![]()
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