Basic Components of the Immune System Flashcards
The process by which hematopoietic stem cells (HSCs) differentiate into mature blood cells is called
Hematopoiesis
Primary lymphoid organs
Bone marrow and the Thymus
regulate the development of immune cells from immature precursors
Secondary lymphoid organs:
•Including the spleen, lymph nodes, and specialized sites in the gut and other mucosal tissues
–Coordinate the encounter of antigen with antigen-specific lymphocytes and their development into effector and memory cells.
HSCs are defined by two capacities:
- The ability to regenerate or “self-renew”
- The ability to differentiate into all diverse blood cell types.
One HSC is present per ________ cells in the bone marrow.
5 x 104 (rare)
Myeloid cells and NK cells:
Are memembers of the innate immune system
First cells to respond to infection or other insults
Lymphocytes are:
Members of the adaptive immune response
Generate a refined antigen specific immune response that also gives rise to immune memory
Granulocytes:

Neutrophils, Basophils, Mast cells, and Eosinophils
- All granulocytes have multilobed nuclei
- The cytoplasm contains granules that are released in response to contact with pathogens

Monocytes:
- Migrate into tissues in response to infection
- Can differentiate into specific tissue macrophages:
- Osteoclasts in the bone
- Microglial cells in the central nervous system
- Alveolar macrophages in the lung
Myeloid Antigen-Presenting Cells:
- Monocytes, macrophages, and dendritic cells
- Professional antigen-presenting cell (APC)
- Considered cellular bridges between the innate and adaptive immune systems
Cells of the Lymphoid Lineage Regulate:
Adaptive Immune Response
Lymphocytes:
Three major populations:
– Principal cell players in the adaptive immune response.
– 20% to 40% of circulating white blood cells and 99% of cells in the lymph.
- B lymphocytes (B cells), expresses B cell Receptor
- T lymphocytes (T cells), expresses T cell Receptor
- No contact With antigen: naïve
- Contact antigen: lymphocytes proliferate and differentiate into both effector cells and memory cells.
- Natural Killer Cells (NK cells)
B Lymphocyte (B cell): Derived its letter from its site of maturation
Bursa of Fabricius in birds
Bone marrow in mammals
Mature B cells Display ___________
- Display B-cell receptor (BCR)
- Membrane-bound immunoglobulin (antibody) molecule that binds to antigen.
- Can recognize soluble or particulate antigen
- – Activated B cells differentiate into effector cells known as Plasma cells
- lose expression of BCR and become highly specialized for secretion of antibody
T Lymphocytes:
Derive their letter (T) from their site of maturation in the thymus
Expresses a unique antigen-binding receptor called the
T-cell receptor
–Only recognize processed pieces of antigen (typically peptides) bound to cell membrane proteins called major histocompatibility complex (MHC)
T lymphocytes are divided into two major cell types:
- T cytotoxic (TC), expresses CD8
- T helper (TH) cells, Expresses CD4
- T helper type 1 (TH1) cells regulate the immune response to intracellular pathogens
- T helper type 2 (TH2) cells regulate the response to many extracellular pathogens.
- T helper type 17 cells (TH17), so named because they secrete IL-17, play an important role in cell-mediated immunity and may help the defense against fungi.
NK Cells
Natural Killer Cells
- They are lymphoid cells that are closely related to B and T cells.
- They do not express antigen specific receptors and are considered part of the innate immune system
- They distinguish cells that should be killed from normal cells. How? By “recognizing” the absence of MHC class I, which is expressed by almost all normal cells.
- Express receptors for immunoglobulins, allows them to bind antibodies specific for pathogens .
- This allows NK cell to releases its granules and induces cell death.
Provides niches for hematopoietic stem cells to self-renew and differentiate into myeloid cells and B lymphocytes
Bone Marrow
Most active sites of hematopoiesis
- Long bones (femur, humerus)
- Hip bones (ileum)
- Sternum
Bone marrow contains several cell types that coordinate HSC development:
- Osteoblasts that generate bone and control the differentiation of HSCs
- Endothelial cells that line the blood vessels and also regulate HSC differentiation
- Reticular cells that send processes connecting cells to bone and blood vessels
- Sympathetic neurons , which can control the release of hematopoietic cells from the bone marrow.
Primary lymphoid organ located above the heart where T cells mature
Thymus
Microenvironments of the thymus
- Cortex which is densely populated with immature thymocytes
- Medulla, which is sparsely populated with mature thymocytes.
- These major regions are separated by the corticomedullary junction (CMJ) : Cells enter from and exit to the bloodstream.
_________ are positively selected in the cortex
__________ are negatively selected in the medulla
Thymocytes
Autoreactive thymocytes
Where the immune response is initiated
Secondary Lymphoid Organs