Cells of the Immune System

Question 1

What is hematopoiesis?

Answer 1

The formation of all blood cells, in bone marrow.

Question 2

What are the leukocyte lineages?

Answer 2

1. lymphoid: lymphocytes (B & T cells, NK cells)

2. myeloid: neutrophils, eosinophils, basophils, dendritic cells, monocytes, macrophages and mast cells

Question 3

What is the make up of leukocytes in the periphery (PBLs) after maturing and leaving the marrow?

Answer 3

neutrophils ~40-75%
lymphocytes 20-50%
monocytes 2-10%
eosinophils 1-6%
basophils < 1%
*many leukocytes reside in tissue, not just blood

Question 4

What is adaptive immunity?

Answer 4

B cells and T cells - have specific and variable antigen recognition receptors
After activation, both give rise to memory cells

Question 5

What is humoral immunity?

Answer 5

Action of B cells that express Ag-specific receptors. They can also secrete soluble receptors as protein antibodies that can bind to circulating antigens.
Receptors are formed during development in the marrow

Question 6

What is cell-mediated immunity?

Answer 6

Action of T cells, which express TCRs. Precursors go from bone marrow to the thymus where the TCRs form and T cells mature.
TCRs require APCs (present Ag as surface peptide on MHC - major histocompatibility complex)

Question 7

What are the major types of T cells?

Answer 7

1. T helper (Th) cells

2. CTLs - cytotoxic T lymphocytes

Question 8

What are the T cell functions?

Answer 8

1. Th cells - activate and coordinate other cells (B and T cells and cells of the innate immune system)
2. CTLs - kill infected/diseased cells

Question 9

List cells of the innate immune system

Answer 9

1. NK cells
2. monocytes, macrophages and dendritic cells
3. neutrophils
4. mast cells, basophils and eosinophils

Question 10

Explain monocytes, macrophages and dendritic cells

Answer 10

• Macrophages are a type of monocyte that have migrated from the bloodstream to another tissue.
• All 3 are capable of receptor-mediated phagocytosis or endocytosis
• activated by PRRs (pathogen recognition receptors), secrete cytokines
• are a link between the innate and adaptive IS because they act as APCs and activate T cells

Question 11

Explain NK cells

Answer 11

Innate lymphoid cells that are cytotoxic and function like CTLs
-memory response in certain settings

Question 12

Explain neutrophils

Answer 12

They are polymorphonuclear leukocytes (PMNs), which have multi-lobed nuclei
Capable of phagocytosis, short-lived cells, no APC fxn, major constituent of pus

Question 13

Explain mast cells, basophils and eosinophils

Answer 13

Mast cells - in tissues, inflammatory mediators, allergies
Basophils - in blood, inflammatory mediators, allergies
Eosinophils - helminth defense, allergies

Question 14

Explain CD nomenclature

Answer 14

CD = cluster of differentiation
Immune cells can be distinguished by microscopic view or by surface proteins (receptors, adhesion molecules, etc)
Not always consistent

Question 15

What are cytokines and what is their function?

Answer 15

Proteins secreted by leukocytes for cell to cell communication.
Regulate characteristics, intensity and duration of immune response
Binds to target cell receptor, which causes signal transduction

Question 16

List categories of cytokines and their functions

Answer 16

1. Interleukins (IL) - released in response to viruses, tumors and biological factors
2. Interferons (IFN) - effect growth & differentiation of hematopoietic immune cells
3. Tumor Necrosis Factors (TNFs) - secreted by inflammatory cells, pro-inflammatory
4. Transforming Growth Factors (TGFs) - help maintain homeostasis in adults
5. Colony Stimulating Factors (CSF) - bind to hematopoietic stem cells & stimulate proliferation
6. Chemokines - can stimulate chemotaxis