18 Questions
What are the major interfaces protected by layers of epithelial cells?
Gastrointestinal tract, respiratory tract, and genitourinary tract
What do antimicrobial peptides, defensins, and cathelicidins do?
Kill bacteria and some viruses by disrupting their outer membranes
Which cells form a mechanical barrier against microbes?
Epithelial cells
Where do microbes mainly come into contact with vertebrate hosts?
Interfaces between the body and the external environment
What are the two pathways of macrophage activation called?
Classical and alternative
What is the source of tissue-resident macrophages?
Progenitors in the yolk sac or fetal liver
Which receptors are involved in the activation and functions of macrophages?
TLRs and NLRs
What are the roles of tissue-resident macrophages?
Ingest and destroy microbes, clear dead tissues, produce cytokines
What induces classical macrophage activation?
Innate immune signals such as from TLRs, and the cytokine IFN-γ
What distinguishes alternative macrophage activation?
It occurs in the absence of strong TLR signals and is induced by the cytokines IL-4 and IL-13.
What activates phagocytosis in macrophages?
Cell surface receptors such as mannose receptors and scavenger receptors
What are tissue-resident macrophages derived from?
Progenitors in the yolk sac or fetal liver early during fetal development
What is the role of intraepithelial lymphocytes in epithelia?
React against infectious agents penetrating the epithelia
What is the primary function of neutrophils and monocytes?
Recognize and ingest microbes for intracellular killing
What stimulates the rapid increase of neutrophils in response to certain infections?
Colony-stimulating factors (CSFs)
Which feature enhances neutrophils' ability to kill ingested microbes?
Expression of receptors for complement activation and antibodies
What do neutrophils initiate at sites of tissue damage?
Clearance of cell debris
What is the primary role of monocytes in extravascular tissues during inflammatory reactions?
Differentiate into macrophages
Study Notes
Immune Functions of Epithelia, Neutrophils, and Monocytes/Macrophages
- Epithelia contain intraepithelial lymphocytes, a type of T cell, which react against infectious agents penetrating the epithelia.
- Epithelia serve as physical barriers and produce antimicrobial substances to prevent infection.
- Neutrophils and monocytes are two types of circulating phagocytes that are recruited to sites of infection to recognize and ingest microbes for intracellular killing.
- Neutrophils are the most abundant leukocytes in the blood, numbering 4000 to 10,000 per μL and rapidly increase in response to certain infections.
- Neutrophils are stimulated by colony-stimulating factors (CSFs) secreted in response to infections, making them the first and most numerous responders to infections, particularly bacterial and fungal infections.
- Neutrophils express receptors for complement activation and antibodies, enhancing their ability to kill ingested microbes.
- Neutrophils are also recruited to sites of tissue damage and initiate the clearance of cell debris.
- Neutrophils have a short lifespan in tissues, providing early defense but not prolonged defense.
- Monocytes are less abundant in the blood than neutrophils, numbering 500 to 1000 per μL, and differentiate into macrophages in extravascular tissues during inflammatory reactions.
- Blood monocytes and tissue macrophages are two stages of the same cell lineage, often referred to as the mononuclear phagocyte system.
- Monocytes and macrophages are involved in the clearance of cell debris and are present in most healthy organs and tissues.
- Neutrophils and macrophages share features such as phagocytosis, chemotaxis, and the ability to migrate through blood vessels into tissues.
Test your knowledge on the components of the innate immune system, including epithelial cells, sentinel cells, circulating and recruited phagocytes, innate lymphoid cells, NK cells, and plasma proteins. Explore the properties and roles of these cells and soluble proteins in innate immune responses.
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