Category: Pathology Principles
The innate immune system is also known as the non-specific immune system. This name makes sense, as this immune system does not target specific pathogens like the adaptive immune system. In innate immunity, pathogens or damaged cells are recognized by pattern recognition receptors (PRRs), which are discussed in depth in the Inflammation section.
The most well-known innate lymphoid cell is the natural killer cell, however more recent developments have shown there are actually numerous ILCs that participate in immunity.
Lymphocytes are the major player in adaptive immunity, or immunity that responds specifically to a pathogen. These lymphocytes have two broad categories: T lymphocytes and B lymphocytes.
Immunodeficiency is caused by lack of function in one or more components of the immune system, preventing an appropriate immune response by the animal. These conditions lead to an increased risk of infections and potentially an increased risk of tumour development.
The major role of eosinophils is in allergic and parasitic disease, particularly helminths.
Cytokines are proteins that are involved in cell signalling by binding to membrane-bound receptors. There are numerous families of cytokines, each with their own set of functions.
Dendritic cells have a major role as an antigen-presenting cell, meaning that they identify foreign antigens and show them to the immune system to enact an immune response. To facilitate this process, dendritic cells are found in tissues throughout the body, and use their long cell processes to maximize their surface area to increase the chance of encountering an antigen.
In order for leukocytes to reach an area of inflammation, they must first be able to move out of the bloodstream. This process is called the leukocyte adhesion cascade, and is mediated by the endothelial cells lining the blood vessels. There are five basic steps in this process: margination, rolling, stable adhesion, transmigration and chemotaxis.
The complement cascade is a series of proteins produced by the liver that are activated sequentially, and ultimately result in the formation of a pore in a target cell. Along the way, the different protein components can have other effects, like chemotaxis, opsonization and interaction with the immune system.
Apoptosis is a controlled process of cell death, involving progressive shrinkage and formation of apoptotic bodies, small fragments of cells with an intact membrane. Because the membrane remains intact, apoptosis is not associated with inflammation, unlike necrosis.