HESI A2 Exam: Immune System
Intro
The immune system protects our bodies from pathogens. The organs of the immune system include the lymph nodes, thymus, bone marrow, and spleen. All immature cells are born in the bone marrow. However, they can mature in different parts of the body.
Adaptive immunity is slower to activate, it specifically targets a pathogen and forms memory cells. B cells, T cells, and antibodies are part of adaptive immunity.
Innate immunity is quick to respond, is not specific to individual pathogens and it does not form memory cells. Examples of innate immunity are macrophages, natural killer cells, and the granulocytes.
Cells of the Innate Immune System
Granulocytes contain reactive oxygen compounds and cytokines and include basophils, eosinophils, and neutrophils.
The three types of granulocytes are basophils, eosinophils, and neutrophils.
Basophils mediate allergic responses.
Eosinophils respond to parasitic infections.
Neutrophils release pro-inflammatory cytokines and phagocytose (eat) bacteria.
A phagocyte is a type of cell that has the ability to ingest foreign particles such as bacteria. It engulfs foreign bodies by extending its cytoplasm into pseudopods (cytoplasmic extensions like feet), surrounding the foreign particle and forming a vacuole.
A monocyte is a type of immune cell made in the bone marrow that travels through the blood to tissues in the body where it becomes a macrophage or a dendritic cell. Monocytes kill extracellular pathogens.
Macrophages are a type of monocyte. Macrophages are large, specialized cells that recognize, engulf and destroy target cells. They are important cells of the immune system that are formed in response to an infection or due to accumulating damaged or dead cells.
Natural killer (NK) cells attack and kill cells that contain intercellular pathogens or display abnormal surface antigens. Tumor cells are an example of NK cells.
Cells of the Adaptive Immune System
T cells are born in the bone marrow and released into the bloodstream as immature lymphocytes. T cells mature in the thymus, differentiating into either helper or cytotoxic T cells.
Helper T cells set off an alarm to warm the immune system that microbes have invaded the body's line of defense. Helper T cells do not directly kill infected cells, as cytotoxic T cells do. Instead they help activate cytotoxic T cells and macrophages to attack infected cells, or they stimulate B cells to secrete antibodies. Helper T cells become activated by interacting with antigen-presenting cells, such as macrophages.
A cytotoxic T cell is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected (particularly with viruses), or cells that are damaged by pathogens in other ways. Cytotoxic T cells are stimulated by antigens and helper T cells. Additionally, cytotoxic T cells kill body cells infected with pathogens by releasing perforin, which ruptures microbial membranes.
B cells, also known as B-lymphocytes, are a type of white blood cell. They function in the humeral immunity component of the adaptive immune system by secreting antibodies. Additionally, B cells present antigen and secrete cytokines.
B cells, unlike the other two classes of lymphocytes, T cells and natural killer cells, express B cell receptors (BCRs) on their cell membrane. BCRs allow the B cell to bind a specific antigen, against which it will initiate an antibody response.
Interleukin-1 activates helper T cells to produce interleukin-2.
Interleukin-2 stimulates B cells to become active antibody secreting plasma cells.
Vaccines work by activating the adaptive immune system, leading to the formation of memory cells. Both memory T and B cells will be formed. Following secondary exposure, these cells will be quickly activated. This means that both the B and T cells will be activated quickly. Memory B cells will produce antibodies, and memory T cells will kill infected cells and activate other immune cells.
More stuff to know
Clonal selection is the fundamental mechanism in immunity. B and T lymphocytes bind to specific pathogenic molecules. Once they have been selected, these B and T lymphocytes make millions of copies of themselves.
Bone marrow is important for producing blood cells, including those that attack infection in the bloodstream. However, these cells do not prevent infections, such as bacteria, from entering the bloodstream.
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