Immunobiology is the branch of biology that deals with the immune system. It covers a wide range of topics from the molecular mechanisms underlying immunity to the clinical manifestations of immunodeficiency diseases. The field of immunobiology has seen tremendous growth in recent years, due largely to advances in our understanding of the molecular basis of immunity.
The immune system is a complex network of cells and molecules that work together to protect the body from infection. The first line of defense against infection is the skin and mucous membranes, which form a barrier to keep out harmful microbes. If these barriers are breached, the immune system kicks into gear to fight off invading microbes.
The cells of the immune system can be divided into two main types: innate immunity and adaptive immunity. Innate immunity is our “first line of defense” against infection; it includes physical barriers like skin and mucous membranes, as well as chemical defenses like stomach acid and enzymes that destroy bacteria. Adaptive immunity is a more sophisticated response that involves special proteins called antibodies that are specific for each invader. Adaptive immunity provides long-lasting protection against specific infections by “remembering” past encounters with them.
The key players in innate immunity are macrophages, neutrophils, dendritic cells, natural killer (NK) cells, and eosinophils. These cells recognize common features on infectious agents (called pathogen-associated molecular patterns or PAMPs), which allows them to mount an effective response without having to “see” the specific invader beforehand. In contrast, adaptive immune responses are initiated by antigen-presenting cells (APCs), which display pieces of invading microbes on their surface (in a process called antigen presentation). This triggers a cascade of events leading to the activation of T-cells and B-cells, which then produce antibodies specifically targeted against the invader. Antibodies neutralize invaders by binding to them and marking them for destruction by other immune cells. They also activate complement proteins, which directly kill bacteria or attract more phagocytes to the site of infection..