Types of immune cells
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Types of Immune Cells
The immune system is a complex network of cells and proteins that defends the body against infection. It can be broadly categorized into innate and adaptive immunity, each comprising various specialized cell types. This article explores the different types of immune cells, focusing on their roles and characteristics.
Innate Immune Cells
Natural Killer Cells and Innate Lymphoid Cells (ILCs)
Natural killer (NK) cells and group 1 innate lymphoid cells (ILC1s) are crucial components of type 1 immunity. These cells produce interferon-gamma (IFN-γ) and are involved in the defense against intracellular pathogens by activating mononuclear phagocytes1. ILC2s, part of type 2 immunity, produce cytokines like IL-4, IL-5, and IL-13, which are essential for combating helminth infections and mediating allergic responses1 4 5. ILC3s, associated with type 3 immunity, produce IL-17 and IL-22, playing a significant role in defending against extracellular bacteria and fungi1.
Dendritic Cells
Dendritic cells (DCs) are professional antigen-presenting cells that capture and process antigens, express co-stimulatory molecules, and secrete cytokines to initiate immune responses. They are pivotal in activating T cells and maintaining immune tolerance to self-antigens7. Plasmacytoid dendritic cells (pDCs) are specialized in producing type 1 interferons during viral infections, linking innate and adaptive immunity10.
Macrophages and Neutrophils
Macrophages are versatile cells involved in phagocytosis, antigen presentation, and cytokine production. They adapt to local tissue environments, displaying tissue-specific features8. Neutrophils are the most abundant white blood cells and are essential for rapid responses to bacterial infections, often recruited by type 3 immunity1.
Adaptive Immune Cells
T Cells
T cells are central to adaptive immunity and can be classified into several subsets based on their functions:
- CD8+ Cytotoxic T Cells (TC1 and TC2): These cells are involved in killing infected or cancerous cells. TC1 cells are part of type 1 immunity, while TC2 cells are associated with type 2 immunity1.
- CD4+ T Helper Cells (TH1, TH2, and TH17): TH1 cells produce IFN-γ and are crucial for type 1 immunity, aiding in the defense against intracellular pathogens. TH2 cells produce IL-4, IL-5, and IL-13, driving type 2 immunity and playing roles in allergic responses and helminth infections1 2 3. TH17 cells produce IL-17 and IL-22, contributing to type 3 immunity and protecting against extracellular bacteria and fungi1.
B Cells
B cells are responsible for antibody production. They can differentiate into plasma cells, which secrete antibodies, or memory B cells, which provide long-term immunity. B cells also act as antigen-presenting cells, contributing to the activation of T cells7 8.
Specialized Immune Cells
Eosinophils, Basophils, and Mast Cells
These cells are primarily involved in type 2 immunity. Eosinophils, basophils, and mast cells are activated by cytokines like IL-4, IL-5, and IL-13, playing roles in allergic reactions and defense against parasitic infections1 4 5.
Nuocytes
Nuocytes are a newly identified type of innate immune cell that expands in response to IL-25 and IL-33. They are a significant source of IL-13 during helminth infections and are crucial for worm expulsion6.
Conclusion
The immune system comprises a diverse array of cells, each with specialized functions tailored to protect the body against various pathogens. Understanding the roles and interactions of these cells is essential for developing targeted therapies for infections, autoimmune diseases, and allergies.
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