A myeloid cell is any cell in the myeloid family, which is one of the two main groups of blood cells. All blood cells develop from hematopoietic stem cells in the bone marrow, creating two cell lines; the myeloid cell line and the lymphoid cell line.
Cells of the myeloid lineage develop from myeloid progenitor cells and include the monocytes, macrophages, dendritic cells, erythrocytes, and platelets.
What is a myeloid cell?
All blood cells develop from multipotent hematopoietic stem cells (HSC) in the bone marrow. HSCs result in two main lines of blood cells; these are the myeloid cells and the lymphoid cells.
HSCs first differentiate into the common myeloid progenitor cells and the common lymphoid progenitor cells. The progenitor cells then further differentiate to produce all cells of the myeloid and lymphoid families. Myeloid progenitor cells lead to monocytes, macrophages, dendritic cells, granulocytes, erythrocytes and platelets.
The process by which blood cells develop from a common precursor cell in the bone marrow is known as Hematopoiesis.
What is myeloid tissue?
Myeloid tissue is also known as Bone marrow. It is the spongy material in the bones that makes blood cells. Myeloid tissue contains and is also called hematopoietic stem cells hematopoietic tissue.
Functions of myeloid cells
The myeloid cells are a diverse group of cells with a wide range of functions. Cells in the myeloid family include the monocytes, granulocytes, macrophages, dendritic cells, erythrocytes, and platelets.
Monocytes make up about 5% of circulating blood cells and are an important part of the innate immune system.
In the event of infection or inflammation, monocytes migrate into the affected tissue and differentiate into macrophages and dendritic cells. Both cells act as phagocytes and quickly remove pathogens and other foreign substances from the infected area. Macrophages and dendritic cells are also antigen presenting cells (APCs) and present antigens on their surface to activate T cells. Hence, they also have important functions in stimulating the adaptive immune response.
The three types of granulocytes are basophils, neutrophils, and eosinophils.
Granulocytes are phagocytic white blood cells that are categorized according to the presence of granules in their cytoplasm, which often contain enzymes to digest enveloped pathogens. They can also contain inflammatory factors (such as histamine), which release granulocytes into the bloodstream in response to allergen exposure.
Macrophages are formed from monocytes that differentiate as they migrate from the bloodstream to infected tissues. In the tissues, macrophages function as scavenger cells and as antigen-presenting cells (APCs). They are found throughout the body and their main function is to trap and destroy pathogens and other harmful substances in their resident tissues. They also present antigens to T cells and release proteins called as Cytokines to activate other cells of the immune system. Therefore, macrophages play an important role in activating the adaptive immune response.
Dendritic cells are important antigen-presenting cells and, like macrophages, are produced by monocyte differentiation. They have long, branched structures (called Dendrites), which make them very efficient at catching and devouring pathogens. Dendritic cells show the antigens of infectious agents on their surface to activate T cells and thus play a central role in initiating the adaptive immune response.
Erythrocytes (AKA red blood cells) also develop from myeloid progenitor cells. Their main function is to deliver oxygen from the lungs to all tissues in the body and to transport carbon dioxide from the tissues to the lungs. Erythrocytes contain the protein Hemoglobin, which binds oxygen in the lungs and releases it to the body’s cells.
Platelets are made by Megakaryocytes; large cells that also develop from the myeloid cell line. Megakaryocytes are located in the bone marrow, where they grow into giant cells before fragmenting into over 1,000 platelets.
The platelets are then released into the bloodstream, where they play a central role in blood clotting. They prevent bleeding by clumping at the site of blood vessel injuries and are essential for wound healing.
What are lymphoid cells
The two most important blood cell lines are the myeloid cells and the lymphoid cells. Lymphoid cells develop from lymphoid progenitor cells and include the T cells, B cells, and natural killer (NK) cells.