Cells and Organs of the Immune System Flashcards
What are the three lines of defense of the body?
1st: (innate immunity) skin, mucous membranes, chemicals
2nd: (innate immunity) phagocytosis, complement, interferon, inflammation, fever
3rd: (adaptive immunity) lymphocytes, antibodies
What are granulocytes or polymorphonuclear leukocytes?
a subgroup of white blood cells characterized by the presence of cytoplasmic granules.
What are granulocytes or polymorphonuclear leukocytes classified as?
- classified as basophils, eosinophils, or neutrophils
Where are granulocytes or polymorphonuclear leukocytes produced?
in the bone marrow
What is the function of a basophil?
- host defense against parasites
- may be involved in allergic and inflammatory reactions
What do basophils contain? What is it used for?
contain toxic granules used to destroy pathogens during process of phagocytosis
What is expressed by basophils?
several adhesion molecules which play critical role in their circulation, including LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18) and CD44
What do eosinophils differentiate from? In response to what?
differentiate from myeloid precursor cells in response to IL-3, IL-5, and GM-CSF
What are the functions of an eosinophil?
- important for host defense against parasites
- may be involved in allergic reactions
What do eosinophils respond to?
chemokines such as CC11/eotaxin-1, CCL24/eotaxin-2, and CCL5/RANTES secreted by lymphocytes or neutrophils
When recruited, what do eosinophils do?
release toxic substances contained in their granules to destroy pathogens and fight infection.
WhatWhat is the most numerous innate immune cell? (50-70%)
Neutrophils
What is characteristic of immature neutrophils? Mature neutrophils?
immature -> band-shaped nucleus
Mature -> segmented nucleus
What do neutrophils do?
circulate in blood stream looking for foreign objects to phagocytose and degrade
How do basophils, eosinophils, and neutrophils stain?
basophils: blue granules
Eosinophils bright red
Neutrophils: neutral pink
What is the number of circulating neutrophils estimated by?
absolute neutrophil count (ANC)
What could a high or low absolute neutrophil count indicate?
High: could be kidney failure, eclampsia or bacterial infection
Low: leukemia, bone marrow damage
How can granulocytes be identified?
expression of CD16, CD34 (immature state) and CD11b/CD18 (activated state)
Where are mast cells generated?
Bone marrow
What are two types of mast cells?
- connective tissue mast cells - local allergic reactions
- Mucosal mast cells - found in areas exposed to the external environment
What do mast cells do?
- defense against parasites
- mediate allergic reactions by releasing inflammatory mediators like histamine
Where are monocytes/macrophages found?
bloodstream and in tissue
What is the difference between macrophages and monocytes?
monocytes circulate in the peripheral blood before entering tissues to replenish tissue-specific macrophage populations
What do macrophages/monocytes do?
- ingest and degrade bacteria
- when activated, coordinate immune response by notifying other immune cells of infection
- recycle dead cells (not an immune function)
What are natural killers cells?
innate immune cells that contain granules filled with proteins that can form holes in a target cell -> can cause apoptosis
- certain population of NK cells have features of both innate and adaptive immunity
What are the functions of natural killer cells?
- recognize and kill virus-infected cells or tumor cells
- cytolytic effectors
- regulators of immune response
What is a major product of natural killer cells?
IFN-gamma, TNF
What are dendritic cells?
specialized sentinel cells that constantly sense and respond to their immediate environment
- hematopoietic bone-marrow-derived cells
Where do dendritic cells mature?
- bone marrow
- lymphoid tissue
- non-lymphoid tissue
What are the functions of dendritic cells?
capture, process, and present antigens to T cells and thus are crucial for bridging innate and adaptive immunity as well as promoting self-tolerance
What happens after a dendritic cells is exposed and take up pathogens?
the maturing DCs travel to secondary lymphoid organs where they become potent T cell activators
How are DCs classified?
- classical/conventional dendritic cells (cDCs)
- plasmacytoid dendritic cells (pDCs)
What ability do plasmacytoid dendritic cells (pDCs) have?
ability to secrete large amounts of type I interferons upon activation through TLR7 and TLR9
What are B lymphocytes?
essential components of the humoral immune response that are activated when they bind to antigens through their receptors (BCR)
Where do B lymphocytes mature?
bone marrow
What do B lymphocytes do?
generate antibodies to specific antigens
What do the antibodies that coat the surface of a pathogen do? (What are their major roles)
- neutralization
- opsonization
- complement activation
When does neutralization occur?
when pathogen is covered in antibodies which renders the pathogen unable to bind and infect the host cells
What is opsonization?
an antibody-bound pathogen serves to alert immune cells, such as neutrophils and macrophages, to engulf and digest the pathogen
What is complement activation?
process for directly destroying or lysing pathogens
What do t lymphocytes begin as and what do they end as?
begin as thrombocytes (precursors to T cells) and end as lymphocytes
What do thrombocytes develop from and where?
develop from hematopoietic stem cells in bone marrow
Where do thrombocytes mature?
in the thymus
What ensures the production of functional T cells?
several stages of selection and quality control
What do T lumphocytes express?
antigen specific receptor (TCR)
What are the two broad categories of T cells? What are the categories based on?
- CD8+ T cells (or cytotoxic T cells or cytotoxic lymphocytes)
- CD4+ T cells
- based on which co-receptor protein is present on cell’s surface
What do CD8+ T cells (or cytotoxic T cells or cytotoxic lymphocytes (CTLs)) do? How?
recognize and kill virus-infected or cancer cells
- have cytotoxic granules containing cytotoxins that kill target cells
What are the four major CD4+ T cell subsets?
- Th1
- Th2
- Th17
- Treg
(Th refers to T helper cell)
What do Th1 cells do?
coordinate immune responses against intracellular pathogens
- produce and secrete molecules that alert and activate other immune cells, like bacteria-ingesting macrophages
What do Th2 cells do?
coordinate immune responses against extracellular pathogens, like helminths, by alerting B cells, granulocytes, and mast cells
What do Th17 cells do?
- produce interleukin 17 which is a signaling molecule that activates immune and non-immune cells
- protect cell surfaces (skin,gut) against extracellular bacteria (recruitment of neutrophils)
What do regulatory T cells (Tregs) do?
monitor and inhibit the activity of other T cells
How do immune cells communicate?
- cell to cell contact
- secreted signaling molecules
What molecules are involved in immune cell communication?
- Cytokines
- Toll-like receptors
- B cell receptors and T cell receptors
- Major Histocompatibility Complex (MHC)
- Complement
What are cytokines?
small proteins with diverse functions such as cell growth, activation, etc.
Where are toll-like receptors expressed?
on innate immune cells like macrophages and dendritic cells
What do Toll-like receptors (TLRs) do?
recognize general microbial patterns and they are essential for innate immune-cell activation and inflammatory responses
What do B cell and T cell receptors do? Where are they found?
recognize foreign antigens
- found on B cells and T cells respectively
What do Major Histocompatibility Complexes (MHCs) do?
- MHC proteins function as carriers to present antigens on cell surfaces and signal whether a cell is a host cell or a foreign cell
What does the complement consist of and what does it do?
consists of a series of proteins found in the blood
- punches a small hole into the pathogen, creating leaks that lead to cell death
- also serve as signalling molecules that alert immune cells and recruit them to area inflammation
