Immune System Cells: Monocytes, Macrophages, and NK Cells

Monocyte and Macrophage

• Engulf pathogens and larger particles, including dead cells and damaged tissues
• Present antigens on MHC class I or II

NK Cells

• Induce IFN-γ production, activating macrophages and cell-mediated immunity
• Kill tumor cells, viral-infected cells, and protozoan-infected cells using granzyme and perforin

Inflammatory Response

• Mediated by cytokines, chemokines, and innate immune cells
• Involves phagocytosis and inflammatory response

Cytokines

• Paracrine: released by producer and acts on neighboring cells
• Autocrine: produced, released, and acts on the producer
• Endocrine: released by producer into the circulation and acts on a distant cell

Interferons

• IFN-α and IFN-β: produced by macrophages, fibroblasts, endothelial, and epithelial cells; activated by viral dsRNA; have antiviral effects
• IFN-γ: produced by lymphocytes and NK cells; activates macrophages

Migration of Cells from Blood Stream into Infected Tissues

• Rolling: a process involving IL-1, TNF-α, and vasodilation
• Involves activation of innate immune cells, such as PMN cells, and the release of chemokines

Innate Immunity and the Inflammatory Response

• Innate immunity: pre-existing defense against infection, mounts an immediate response to infectious agents
• Activation of innate immunity leads to an inflammatory response

Components of Innate Immunity

• Physical barriers: skin, mucous membranes, and epithelial cells
• Chemical and biochemical barriers: lysozyme, fatty acids, HCL, and lactic acid

Antimicrobial Peptides in Secretions

• Defensins: found in mucosal and skin secretions
• Cathelicidins: found in mucosal secretions
• Collectins: bind to polysaccharides on microbes

Lymphoid Organs

• Primary: bone marrow (B cell maturation) and thymus (T cell maturation)
• Secondary: lymph nodes, spleen, and MALT (Payer’s patch)

Lymphatic Vessels and Spleen

• Lymphatic vessels connect tissues with lymph nodes and contain lymphocytes and tissue dendritic cells
• Spleen deals with antigens shed into the bloodstream and is not connected to lymphatic vessels

Innate Immune Cells

• Mast cells: involved in hypersensitivity and release histamine, heparin, and proteolytic enzymes
• Basophils: involved in hypersensitivity and release histamine, heparin, and proteolytic enzymes
• Eosinophils: involved in hypersensitivity and parasitic infection, and release toxic agents
• Neutrophils: phagocytose small pathogens and release oxygen radicals

Killing and Degradation

• Lysosomal dependent: involves chlorine products, defensins, and proteolytic enzymes
• Non-lysosomal dependent: involves respiratory burst, oxygen radicals, and NO (inhibits viral replication)

MHC Class I and II

• MHC class I: presents endogenous peptides, involved in antigen presentation, and leads to cytotoxicity
• MHC class II: presents extracellular antigens, found on antigen-presenting cells, and signals the activation of other immune cells and their inflammatory responses

Quiz about the functions of monocytes, macrophages, and NK cells in the immune system, including antigen presentation, pathogen elimination, and inflammatory response.