The immune system protects its host from infection with layered defenses of increasing specificity. Physical … See more

Several barriers protect organisms from infection, including mechanical, chemical, and biological barriers. The waxy cuticle of most leaves, the exoskeleton of insects, the shells and membranes of externally deposited e… See more

Microorganisms or toxins that successfully enter an organism encounter the cells and mechanisms of the innate immune system. The innate response is usually triggered when microbes are identified by pattern recognition … See more

The adaptive immune system evolved in early vertebrates and allows for a stronger immune response as well as immunological memory, where each pathogen is "remembered" by a signature antigen. The adaptive im… See more

The immune system is involved in many aspects of physiological regulation in the body. The immune system interacts intimately with other systems, such as the endocrine and the nervous systems. The immune sy… See more

Failures of host defense occur and fall into three broad categories: immunodeficiencies, autoimmunity, and hypersensitivities.
Immunodeficiencies occur when one or more of th… See more