What are Myeloid Cells?
Myeloid cells are a diverse group of cells derived from the myeloid lineage of hematopoietic stem cells. These cells are crucial for the body's defense mechanisms and include various types such as
granulocytes, monocytes, macrophages, and dendritic cells. They play a pivotal role in innate immunity, inflammation, and tissue repair.
1.
Granulocytes: Includes
neutrophils, eosinophils, and basophils.
2.
Monocytes: These cells circulate in the bloodstream and differentiate into macrophages and dendritic cells upon entering tissues.
3.
Macrophages: Large phagocytic cells that engulf and digest cellular debris and pathogens.
4.
Dendritic Cells: Specialized antigen-presenting cells that activate T-cells and initiate adaptive immune responses.
Where are Myeloid Cells Found?
Myeloid cells are found throughout the body. Granulocytes and monocytes circulate in the bloodstream, while macrophages and dendritic cells are found in various tissues. Specific locations include:
- Bone Marrow: Site of myeloid cell production.
- Bloodstream: Pathway for granulocytes and monocytes.
- Tissues: Macrophages and dendritic cells reside in tissues such as the liver (Kupffer cells), lungs (alveolar macrophages), and skin (Langerhans cells).
- Neutrophils: Rapidly respond to infections by phagocytosing bacteria and releasing enzymes.
- Eosinophils: Combat parasitic infections and modulate allergic reactions.
- Basophils: Release histamine and other mediators during allergic responses.
- Monocytes/Macrophages: Engulf pathogens and dead cells, present antigens to T-cells, and release cytokines.
- Dendritic Cells: Capture and present antigens, initiating adaptive immunity.
- Hematoxylin and Eosin (H&E) Stain: Commonly used to differentiate cell types based on morphology.
- Immunohistochemistry (IHC): Uses antibodies to detect specific antigens; markers such as CD11b for myeloid cells, CD68 for macrophages, and CD1c for dendritic cells.
- Cytochemical Stains: Specific dyes like Wright-Giemsa for blood smears can highlight features of granulocytes and monocytes.
- Leukemias: Malignancies of myeloid cells, such as acute myeloid leukemia (AML).
- Myelodysplastic Syndromes (MDS): Group of disorders caused by poorly formed or dysfunctional myeloid cells.
- Chronic Inflammatory Diseases: Conditions like rheumatoid arthritis involve dysregulated myeloid cell activity.
- Infections: Myeloid cells are key players in the response to bacterial, viral, and fungal infections.
Conclusion
Understanding myeloid cells is essential in histology as they are integral to immune responses, inflammation, and homeostasis. Advances in histological techniques continue to enhance our knowledge of their roles in health and disease, providing insights into novel therapeutic approaches.
