Lecture 12: Leukocytes

Morphology, Kinetics, & Functions

What is the morphology of these two neutrophils?

left: band

right: mature

True or false: neutrophils are granulocytes with lysosomes containing hydrolytic enzymes and anitbacterial agents.

true

When do primary granules appear in granulocytes?

late myeloblast/early promyelocyte stage

When do secondary granules appear in granulocytes?

in myelocytes

What is the granulocyte equivalent of neutrophils in birds and reptiles, but with variably stained red granules?

heterophils

What is commonly mistaken for eosinophils in histopathology, with variably stained red granules?

heterophils

Some lymphocytes recirculate from tissues to ______.

blood

Some monocytes may shuttle back to ________.

bone marrow

What is the half-life of neutrophils in blood?

5-10 hours

How long do neutrophils usually survive in tissues?

a few days

What occurs if neutrophils remain in blood after half-life?

spontaneous apoptosis

What is the half-life in blood of eosinophils and basophils?

E: less than one day

B: 2-3 days

How long do eosinophils and basophils survive in tissues?

E: weeks to months

B: a few days

Where is a marginating pool of monocytes found?

within lung capillaries

How do monocytes survive weeks to months in tissues?

develop into macrophage and dendritic cells

Where are most lymphocytes found?

lymphoid organs

What percentage of total lymphocytes are found in the blood?

2-5%

What type of lymphocyte are most blood lymphocytes?

naive T and B lymphocytes

What is the function of high endothelial venules (HEVs)?

bind lymphocytes and facilitate movement from blood in lymphoid organs

What is the half-life in blood of circulating lymphocytes?

about 30 minutes

How long do lymphocytes take to migrate through a lymph node?

about one day

True or false: memory lymphocytes will return to any tissue.

false: they favor return to a similar type of tissue

True or false: proliferating cell exhibit minimal migration

true

How long do B-lymphocytes survive vs their proliferating clones?

2-3 weeks individual cells, clones for years

What is the main function of neutrophils?

recognize chemoattractants, migrate through the tissues and destroy invading bacteria

Why do neutrophils require various surface adhesion molecules?

• adhesion and spreading

• haptotaxis (chemotaxis except surface bound movement)

• phagocytosis

What are some examples of neutrophil activants?

• opsonized particles, immune complexes, bacterial products, GM-CSF, G-CSF, and chemoattractants produced during inflammation

• tight binding of Beta-2 integrin to intracellular adhesion molecules (ICAMs)

• activated endothelial cells

• superoxide generation, degranulation

What is the mechanism of neutrophilic haptotaxis?

receptors for chemoattractants increased following activation → crawl using Beta1-3 integrin molecules binding to appropriate adhesion molecules within extracellular matrix

What are the chemoattractants involved in neutrophilic haptotaxis?

• IL8 and other chemokines

• C5a, PAF, leukotriene B4

• bacterial products recognized by TLRs

Describe the steps of neutrophilic attachment.

random contact (endothelial cell activation) → rolling (selectins) → firm adhesion (leukocyte activation) → diapedesis (integrins) → haptotaxis & chemoattractants

What important neutrophilic enzyme is responsible for hypochlorous acid production?

myeloperoxidase

What are some leukocyte mechanisms of killing?

• direct damage from reactive oxygen species (ROS) including the superoxide free radical

• enzymes: collagenase, acid and neutral hydrolases, lysozyme

• nonenzymatic protein molecules in granules

• myeloperoxidase enhanced H2O2 killing

What are the nonenzymatic protein molecules in granules responsible for killing?

• cationic proteins and peptides including defensins which are inserted in lipid bilayer

• lactoferrin binds iron

What is required by NETosis to bind and kill bacteria, fungi, parasites, and possibly some viruses?

production of superoxide free radicals

True or false: NETosis is an active form of cell death that is different from apoptois or necrosis.

true

What leukocyte has little phagocytic ability, with poor defense against bacteria and viruses?

eosinophils

Where are most tissue eosinophils found?

GI mucosa

What is the function of eosinophils?

respond to type 2 cytokine-induced inflammation:

• produces type 1 hypersensitivity allergic reactions

• host defense against helminths (roundworms, flukes)

What is used to kill organisms too large to phagocytize, such as helminths?

oxygen metabolites and major basic protein, eosinophil cationic proteins, and eosinophil neurotoxin from granules damage/kill helminths

What type of leukocyte is this?

basophil

What is the site of maturation for basophils vs mast cells?

B: marrow

M: tissues

Are mature basophil and mast cells normally found in tissues?

B: no

M: yes

How long do basophils survive vs mast cells?

B: days

M: weeks to months

Why do basophil and mast cell granules have a purple color?

histamine is bound to polyanions such as heparin

When are basophils recruited?

to sites of inflammation after exposure to allergens, helminths, ectoparasites

What is the function of basophil and mast cells?

• release histamine and other mediators following antigen-IgE binding

• contribute to inflammation: expulsion of parasites and eosinophil recruitment

What is this?

monocytes

What is the function of monocytes?

• migrate into tissue to become macrophages and dendritic cells

• phagocytosis, antigen presentation to T lymphocytes, cytokine production (inflammation, hematopoiesis)

What type of cell is rapidly mobilized from marrow in response to inflammatory conditions?

monocyte

True or false: monocyte chemoattractants are similar to neutrophils.

true

What are monocytes less and more effective against?

• less effective against bacteria

• more effective against viruses, protozoa, and fungi

What promotes the transformation of monocytes to macrophages?

M-CSF

What are the two types of macrophages?

M1: antimicrobial

M2: wound repair, tissue remodeling

What increases when monocytes transform to macrophages?

increased size, granules, mitochondria, phagocytic capacity

What cell has more staying (synthesize new membranes and lysosomes) than neutrophils?

neutrophils

True or false: macrophages migrate faster than neutrophils

false

What two types of immunity do macrophages link?

innate and adaptive:

• TLRs recognize bacterial molecules

• Fc and complement receptors for opsonized microorganisms

What antimicrobial properties do macrophages have?

• NADPH oxidase, but less myeloperoxidase than neutrophils

• Nitric oxide more important free radical for killing

What do macrophage scavenger receptors bind?

• aged or damage cells

• necrophagocytosis

What role do macophages play in immune modulation?

• antigen processing

• tumor cell killing after sensitization by T lymphocytes

• synthesis of various cytokines

True or false: macrophages play a role in wound healing.

true

What two lymphocytes have granules?

1. cytotoxic T lymphocytes

2. NK cells

What is the function of T lymphocytes?

cellular immunity & produce cytokines that effect hematopoiesis

What do CD8+ cytotoxic T cells do?

antigen-dependent cells that destroy target cells (ex. neoplastic cells or virus-infected cells)

What do CD4+ Th lymphocytes do?

provide defense against pathogens and neoplasia by recruiting and activating various immune cells

What are the functions of B lymphocytes?

• intact antigens recognized and bound to B cell receptors (BCRs)

• immunoglobulin production with participation from T lymphocytes, DCs, and macrophages

• following activation → Ig-producing immunoblasts and plasma cells are produced

What immunoglobulin is produced by B lymphocytes initially, and what is produced after continued antigenic stimulation?

IgM → IgG

Plasma cells

What is the function of an NK cell?

bind to target tumor cells and virus-infected cells and induce apoptosis similar to cytotoxic T lymphocytes