Lecture 6 - Leukocyte Physiology and Function

Question 1

Functions of Myeloid Cells

Answer 1

1. The ability to migrate out of circulation into tissues
2. The ability to undertake phagocytosis
3. The ability of the release of cytoplasmic granule content by exocytosis

Question 2

Mechanisms of Neutrophil Emigration

Answer 2

Stages of emigration from the circulation to tissues
Rolling
- mediated by selectins
- loose adherence to endothelium
Firm Adhesion 
- mediated by integrins
- e.g. WBC: LFA1
- cell firmly attached to endothelium
Migration
- mediated by PECAM (platelet endothelial cell adhesion molecule)
- cytoskeletal changes in WBC form pseudopodia that pass between endothelial cells
Direction is determined by chemotaxis

Question 3

Neutrophil Chemotaxis

Answer 3

Directed movement towards attractant 
Chemoattractant substances include:
- N-formyl oligopeptides
- C5a, C3b (complement)
- interleukin 8 (monocyte)
- leukotriene B4 (membrane phospholipid)
- platelet activating factor (endothelium)
Movement via repetitive wavelike motion resulting from changes in cell's cytoskeleton

Question 4

Neutrophil Phagocytosis

Answer 4

Neutrophils have phagocytic role in the tissues
- need to be able to digest phagocyte, ingest and kill and digest
Increase phagocytic efficiency with opsonisation
- e.g. IgG, C3b
Formation of phagolysosome
Release of substances into phagolysosome
- preformed
- generated

Question 5

Neutrophil Granule Contents

Answer 5

Primary granules
- myeloperoxidase
- elastase
- defensins
Secondary granules
- lactoferrin
- collagenase
- lysozyme
- histaminase
Tertiary granules
- gelatinase

Question 6

Oxygen Dependent Mechanisms

Answer 6

Generated (rather than pre-existing)
Cause damage to cell membrane
Effective at killing microorganisms
May damage host tissue

Question 7

Quantitative Leukocyte Changes

Answer 7

For example:

• changes in circulating [leukocytes] (from expected values/R.I)
• may have increased or decreased []
• total [WBC] may be altered
• individual (or one or more) leukocyte [] may be altered

Question 8

Definitions of the suffixes -cytosis, -philia and -penia

Answer 8

• cytosis - increased [] of cells e.g. leukocytosis, lymphocytosis, monocytosis
• phila - increased [] of circulating cells e.g. neutrophilia, eosinophilia, basophilia
• penia - decreased [] of circulating cells e.g. leukopenia, neutropenia, eosinopenia

Question 9

Leukocytosis

Answer 9

Increased concentration of leukocytes (> than upper limit)
Usually caused by a neutrophilia
Uncommonly caused by lymphocytosis
Rarely caused by monocytosis, eosinophilia and basophilia

Question 10

General Mechanisms of Quantitative Changes

Answer 10

We sample cells from the circulating pool but may be affected by ‘other pools’
Increased leukocytes
- increased production in the bone marrow
- decreased migration from the circulation
- movement from marginated pool to circulating pool
Decreased leukocytes
- decreased production in the bone marrow
- increased migration from the circulation
- movement to ‘another’ pool from circulating pool
- destruction of leukocytes

Question 11

Neutrophilia

Answer 11

Neutrophils >7.0 x 10^9/L
Commonly observed 
Commonly due to
- inflammation
- stress
- myeloproliferative disease

Question 12

Neutropenia

Answer 12

Neutrophils <1.5 x 10^9/L
Commonly observed
Commonly due to
- severe, acute inflammation
- immune-mediated processes
- disorders of bone marrow

Question 13

Lymphocytosis

Answer 13

Lymphocytes > 5.0 x 10^9/L
Commonly observed
Commonly due to
- inflammation, especially viral inflammation
- chronic inflammation
- lymphoid neoplasia

Question 14

Monocytosis

Answer 14

Monocytes > 1.0 x 10^9/L
Often accompanies disorders of neutrophils
Lesser magnitude than neutrophils
Commonly due to:
- inflammation, especially chronic/ongoing
- myeloproliferative disease

Question 15

Eosinophilia

Answer 15

Eosinophils > 0.6 x 10^9/L
Less common than disorder of neutrophils
Less magnitude than disorders of neutrophils
Commonly due to:
- parasitic disease
- allergic disease
- myeloproliferative disease

Question 16

Basophilia

Answer 16

Basophils > 0.2 x 10^9/L
Uncommonly observed
May occur with:
- myeloproliferative disease e.g. CML
- allergic disease e.g. hypersensitivity 
- infectious disease e.g. chickenpox
- miscellaneous e.g. diabetes, radiation

Question 17

Neutrophil Function

Answer 17

Decreased function may manifest as a consequence of defects of:
- migration
- phagocytosis
- killing
Function is not directly assessed by concentration
In some cases atypical morphology may indicate abnormal function
- e.g. abnormal secondary granules in Chediak-Higashi syndrome
- e.g. abnormal nucleus in Pelger-Huet anomaly

Question 18

Assessment of Neutrophil Function (Tests)

Answer 18

Presence/lack of myeloperoxidase
- cytochemical stain for myeloperoxidase
Generation of superoxide
- nitroblue tetrazolium dye test
Expression of cell surface receptors
- flow cytometry
Granule structure
- electron microscopy