Immune Cell Lineages

The Immune System Structures and Cell Types
Lymphatic & Immune Systems
Systems Biology

Systems Biology

Immune cells, also known as leukocytes, originate from hematopoietic stem cells found in bone marrow. These stem cells differentiate into myeloid and lymphoid progenitor cells. Myeloid-derived immune cells are part of the innate immune system and include neutrophils, basophils, eosinophils, monocytes, macrophages, and dendritic cells. Neutrophils phagocytize pathogens, while basophils and mast cells release histamines contained in their granules, triggering allergic responses. Eosinophils also trigger allergic responses indirectly by acting on basophils and mast cells. Monocytes initially circulate in the blood but eventually differentiate into phagocytic macrophages and dendritic cells, which communicate essential information about pathogens to the adaptive immune system.

Lymphoid-derived cells, or lymphocytes, are either innate or adaptive immune cells. Natural killer cells are innate immune cells that target abnormal body cells for destruction. B- and T-lymphocytes are adaptive lymphoid cells. B-cells mature in the bone marrow and differentiate into antibody-secreting plasma cells or memory B-cells. T-cells mature in the thymus and either destroy infected cells (CD8+ cytotoxic T-cells) or coordinate and control immune responses (CD4+ helper T-cells). Both B- and T-cells are naive until exposed to a specific pathogen, which makes them part of the adaptive immune system.

Lesson Outline

<ul> <li>Immune cells (leukocytes) <ul> <li>Originate from hematopoietic stem cells in bone marrow</li> <li>Differentiate into myeloid and lymphoid progenitor cells</li> </ul> </li> <li>Myeloid-derived immune cells (innate immune system) <ul> <li>Neutrophils - phagocytize pathogens</li> <li>Basophils & mast cells - release histamines, trigger allergic responses</li> <li>Eosinophils - contrain granules that are toxic to certain internal parasites and trigger allergic responses indirectly by acting on basophils and mast cells</li> <li>Monocytes - circulate in blood, differentiate into macrophages and dendritic cells</li> <li>Macrophages - phagocytize pathogens and cellular debris</li> <li>Dendritic cells - communicate information about pathogens to adaptive immune system</li> </ul> </li> <li>Lymphoid-derived cells (lymphocytes) <ul> <li>Innate or adaptive immune cells</li> <li>Natural killer cells - innate, target abnormal body cells for destruction</li> <li>B- and T-lymphocytes - adaptive lymphoid cells</li> <li>B-cells <ul> <li>Mature in bone marrow</li> <li>Differentiate into antibody-secreting plasma cells or memory B-cells</li> </ul> </li> <li>T-cells <ul> <li>Mature in thymus</li> <li>CD8+ cytotoxic T-cells - destroy infected cells</li> <li>CD4+ helper T-cells - coordinate and control immune responses</li> </ul> </li> <li>B- and T-cells - naive until exposed to a specific pathogen (adaptive immune system)</li> </ul> </li> </ul>

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What are the main types of immune cell lineages and how do they develop from hematopoietic stem cells?

The two main immune cell lineages are myeloid and lymphoid cells. They both develop from hematopoietic stem cells found in the bone marrow. Hematopoietic stem cells differentiate into either myeloid progenitor cells or lymphoid progenitor cells. Myeloid progenitor cells give rise to innate immune cells, such as granulocytes, monocytes, and dendritic cells, whereas lymphoid progenitor cells give rise to adaptive immune system cells, such as B-cells, T-cells and natural killer cells.

How do leukocytes fit into the classification of immune cell lineages?

Leukocytes, or white blood cells, are a broad category of immune cells that include both myeloid and lymphoid cells. They can be divided into granulocytes and agranulocytes based on the presence or absence of granules in their cytoplasm. Granulocytes, which include neutrophils, eosinophils, and basophils, are part of the myeloid lineage. Agranulocytes include lymphoid lineage cells such as B-cells, T-cells, and natural killer cells, as well as myeloid lineage cells like monocytes, macrophages, and dendritic cells.

What is the role of granulocytes in the immune system, and how do they perform phagocytosis?

Granulocytes are a type of innate immune cell that includes neutrophils, eosinophils, and basophils. They play a crucial role in the immune response by defending against pathogens and mediating inflammation. Granulocytes, particularly neutrophils, perform phagocytosis by engulfing and destroying foreign substances such as bacteria, viruses, and other microbes. They recognize the pathogen, attach to it, engulf it, and break it down using enzymes and chemicals stored in their granules.

How do natural killer cells function in the immune response, and do they belong to the innate or adaptive immune system?

Natural killer (NK) cells are lymphocytes that play a crucial role in the innate immune system. They function by detecting and killing virus-infected cells and cancer cells. NK cells recognize abnormal cells by detecting the presence of certain ligands on their surface or the lack of self-MHC markers. Upon recognition, NK cells release cytotoxic granules containing perforins and granzymes, which induce apoptosis (cell death) in the target cell. They provide the first line of defense against infectious agents and play a key role in controlling some viral infections before the adaptive immune system can respond.

What are the key differences between B-cells and T-cells in the adaptive immune system?

B-cells and T-cells are both lymphocytes that play crucial roles in the adaptive immune system, but they have distinct functions. B-cells are responsible for producing and secreting antibodies (immunoglobulins), which recognize and bind to specific antigens, neutralizing them or targeting them for destruction by other immune cells. B-cells differentiate into antibody-secreting plasma cells and memory B-cells, which can respond more rapidly to subsequent infections with the same antigen. T-cells, on the other hand, have two main types: CD4+ helper T-cells and CD8+ cytotoxic T-cells. Helper T-cells activate other immune cells, such as B-cells, macrophages, and cytotoxic T-cells, by releasing cytokines. Cytotoxic T-cells directly kill virus-infected cells and cancer cells by inducing apoptosis. Both B-cells and T-cells require activation by antigen-presenting cells, such as dendritic cells, for a proper immune response.