Macrophages are a type of white blood cell that are derived from monocytes in the blood. They are phagocytic in nature and can take on a variety of forms, such as Kupffer cells in the liver, mesangial cells in the kidney, and alveolar macrophages in the lung. Microglial cells are the macrophages associated with the central nervous system.

Red Blood Cells (RBCs) are the most common type of blood cell and are not part of the immune system. RBCs are responsible for carrying oxygen and carbon dioxide throughout the body. They are produced in the bone marrow and have a lifespan of about 120 days. Unlike other blood cells, RBCs do not contain a nucleus and are unable to divide. They are also unable to recognize and respond to foreign substances, making them unable to fight off infections.

Chediak-Higashi syndrome is an autosomal recessive disorder which is caused by the deficiency of NK cells. It is characterized by partial albinism, recurrent infections, and a bleeding tendency. NK cells are a type of white blood cell that helps the body fight off infections.

An immune response is a reaction of the body's immune system to a foreign substance, such as a virus, bacteria, or toxin. When the body is exposed to a nonself particle, it triggers an immune response, which is the body's way of defending itself. The body recognizes the nonself particle as an antigen and produces antibodies to fight it. Antibodies are proteins that recognize and bind to antigens, helping the body to destroy them.

Immunology is the branch of biology that studies the immune system, which is the body's natural defense against disease-causing agents such as bacteria, viruses, and parasites. It is a complex system that involves many different types of cells, organs, and molecules that work together to protect the body from infection and disease. Immunology also studies how the immune system develops and changes over time, as well as how it can be manipulated to treat and prevent diseases.

Costimulation is the process by which a helper T cell is activated when it binds to a class II MHC protein on a displaying cell. This process is necessary for the T cell to become activated and to initiate an immune response. Costimulation is a key step in the activation of the immune system, as it helps to ensure that the immune system only responds to foreign antigens and not to self-antigens.

Follicular dendritic cells do not function as antigen presenting cells as they do not originate from the bone marrow and do not express MHC II molecules on their surface.

SCID stands for Severe Combined Immunodeficiency where very few T-lymphocytes are formed and B-lymphocytes are also deficient. As a result, the patient dies of even minor infections.

Memory cells are a type of immune cell that are able to quickly respond post any subsequent encounter with the same antigen. Memory cells are generated after an initial encounter with an antigen, and are able to recognize and respond to the same antigen more quickly and effectively than the initial response. Memory cells are a key component of the adaptive immune system, and are responsible for providing long-term immunity to a pathogen.

Interferons are a type of cytokine, a protein produced and released by host cells in response to the presence of pathogens such as viruses, bacteria, parasites, or tumor cells. They are part of the body's natural defense system, and are produced by cells in response to the presence of pathogens. Interferons help to regulate the immune system by stimulating the production of other cytokines, which in turn activate the immune system to fight off the invading pathogen.