The Cells of the Immune System (Week 2) Flashcards
Stem Cells have…
- the ability to regenerate or “self-renew”
- the ability to differentiate from young, immature cells into diverse and mature cell types with specialized function
Embryonic stem cells
- Pluripotent
- give rise to all cell types in the body
Adult stem cells
- multipotent
- give rise to tissue-specific cell types
Hematopoietic stem cell (HSC)
the stem cell that all of our immune cells originate from
Hematopoiesis
maturation of HSC into immune cells
Where is the primary site of development for adult immune cells?
primary lymphoid organs
- bone marrow
- thymus
Stromal cells
specialized cells that maintain
the niche for immune cell development in these lymphoid organs
Thymus
- primary lymphoid tissue
- One specific immune cell precursor
leaves the bone marrow and develops
to a mature immune cell in the thymus - site of immune cell development
Leukocytes (white blood cells) arise from…
2 progenitor cells:
1. myeloid progenitor = myeloid cells
2. lymphoid progenitor = lymphocytes
Myeloid progenitors give rise to…
- Leukocytes in the innate immune system
- Red Blood Cells (RBCs)
- Megakaryocytes and Platelets for clotting
Granulocytes (Polymorphonuclear Cells)
- First responders to infection
- Multi-lobed nuclei
- Cytoplasmic granules
- Intracellular membrane-bound vesicles
- Release contents during infection =
Degranulation - Contain proteins to harm pathogens, recruit immune cells or remodel tissue
Neutrophils
- granulocytes
- short-lived
- Highly mobile
- Infection -> Leukocytosis = temporary increase in neutrophil development
- Phagocytes
- granules have anti-microbial properties and help remodel tissue
- undergo NETosis
Eosinophils
- granulocyte
- Mobile
- Important for parasite infections
- Granules damage parasite membranes
- Secrete cytokines regulating immune
responses - Contribute to allergies and asthma where parasites are not common
Basophils
- granulocyte
- Non phagocytic
- Important for parasite infections
- Granules contain histamine: Increases immune cell recruitment/tissue remodeling
- Secrete cytokines regulating immune responses
- Contribute to allergies and asthma where parasites are not common
Mast cells
- granulocyte
- non phagocytic
- similar to basophils
- Important for parasite infections
- Granules contain histamine: Increases immune cell recruitment/tissue remodeling
- Contribute to allergies and asthma where parasites are not common
Monocytes
- Migrate and differentiate into tissue resident phagocytes
- 2 types: inflammatory and patrolling
Inflammatory monocytes
enter issues upon infection
- differentiate into macrophages
Patrolling monocytes
crawl along and monitor blood vessel repair
How do immature dendritic cells (DCs) capture antigen?
through phagocytosis, endocytosis or pinocytosis (intake of extracellular fluid) and get activated
Lymphoid progenitors give rise to…
- Lymphocytes in the adaptive immune system
- Innate Lymphoid Cells (ILCs)
What are the different lymphocytes?
- ILCs (innate lymphoid cells): part of innate immunity
- T cells: differentiate into helper or cytotoxic (killer) T cells
- B cells: differentiate into plasma cells to secrete antibodies
- and dendritic cells
B Lymphocytes
- Every B cell (B lymphocyte) has
a unique B cell receptor (BCR) - BCR is membrane-bound,
surface version of an antibody - Naïve, mature B cells are
activated by antigen - BCRs recognize antigen in any
form (soluble and particulate)
triggering activation of the B cell - Activated B cells are pAPCs
Plasma cells
- Some activated B cells differentiate into Plasma cells
- Plasma cells have no surface, membrane-bound BCR
- Secrete 100s-1000s of antibody per second
- Some are short-lived and some are long-lived
T lymphocytes
- develop in the Thymus
- T cells have a T Cell Receptor (TCR)
- TCRs recognize peptides attached to MHC molecules of APCs (MHC I) and pAPCs (MHC II)
- either helpers or cytotoxic, distinguished by a specific molecule
Helper T lymphocytes (CD4)
- recognize pAPCs
- get activated by pAPCs and
also activate the pAPC - subtypes are specific to the
type of pathogen (based on cytokines) - environment in which they get
activated influences this - Named for the cytokines they secrete
- Regulatory T cells (Treg) are inhibitory to control inflammation
Cytotoxic T lymphocytes (CD8)
- recognize all the cells in our body
- monitor our cells for infection
- Eliminate cells presenting non-self antigens
- Differentiate into Cytotoxic T lymphocyte (CTL) upon recognition of non-self antigen on cells
- CTLs release cytotoxins that poke holes in cell membrane and cause apoptosis
Innate Lymphoid Cells (ILCs)
- No antigen-specific receptors
- 3 groups: ILC1, ILC2, ILC3 (based on cytokines)
Natural Killer (NK) cells
- ILCs
- Cytotoxic cells that attack
abnormal cells - Recognize a lack of MHC
molecules and release cytotoxic
granules to kill the cell
Antigen receptors (B cells vs T cells)
- B cell receptors (BCR) can recognize antigen in any form, particulate or soluble
- T cell receptors (TCR) can only recognize antigen as a peptide
presented on an MHC molecule (require antigen presentation)
Antigen presentation
- displaying peptides of antigen/pathogen
- Peptides are presented on Major Histocompatibility Complex (MHC) Molecules
- All cells have surface MHC I
- Professional antigen presenting cells (pAPCs) have surface MHC II
- pAPCs get activated, phagocytose pathogens, digest proteins into peptides, load them onto MHC II
