Disorders of Granulocyte/Monocyte Function

Question 1

Name the normal functions of neutrophils (4)

Answer 1

adherence, chemotaxis, ingestion, and degranulation/microbicidal activity

Question 2

Adherence:

Answer 2

Neutrophils pulled to areas of infection by interacting with endothelial cells in a rolling motion. This is followed by a more extensive process of firm adhesion mediated by a separate set of adhesion proteins.

Question 3

Chemotaxis:

Answer 3

Passing through the junctions between endothelial cells (diapedesis), the cells move towards the offending organisms (chemotaxis), following the trail of chemoattractants

Question 4

Ingestion:

Answer 4

At the site of infection, the microbe, properly opsonized with C3b or antibody, is enveloped by pseudopods which, like arms, embrace the organism. With fusion of the pseudopods, a phagosome is formed encasing the ingested particle in a small volume.

Question 5

Degranulation/Microbicidal activity:

Answer 5

Granules of each class fuse with the growing phagolysosome and the oxidase enzyme system is assembled in the membrane initiating the respiratory burst and generating reactive oxygen species. The reactive oxygen species (ROS) + oxygen independent mechanisms –> death and dissolution of the microbe

Question 6

Explain how neutrophil function is affected in the following disorders: leukocyte adhesion deficiency (LAD) I

Answer 6

Neutrophilia. Decreased adherence to endothelial surface leading to a defect in movement of neutrophils to infected tissue sites.

Question 7

Explain how neutrophil function is affected in the following disorders: leukocyte adhesion deficiency (LAD) II

Answer 7

Neutrophilia. Decreased rolling on endothelial surfaces as a prelude to tight adherence. RBC also affected, abnormal ABH antigens.

Question 8

Explain how neutrophil function is affected in the following disorders: actin dysfunction

Answer 8

↓ chemotaxis. ↓ ingestion.

Question 9

Explain how neutrophil function is affected in the following disorders: specific granule deficiency

Answer 9

Decreased chemotaxis and microbicidal activity.

Question 10

Explain how neutrophil function is affected in the following disorders: myeloperoxidase deficiency

Answer 10

Partial or complete deficiency of myeloperoxidase. Mild defect in killing bacteria, significant defect in killing candida

Question 11

Explain how neutrophil function is affected in the following disorders: Chediak-Higashi syndrome

Answer 11

Neutropenia. Giant granules in all leukocytes. Abnormal degranulation. Major defect in movement, also decreased degranulation and microbicidal activity.

Question 12

Explain how neutrophil function is affected in the following disorders: chronic granulomatous disease (CGD).

Answer 12

Neutrophilia. Normal adherence, chemotaxis, ingestion and degranulation. Defect in oxidase enzyme system. No toxic oxygen metabolites produced.

Question 13

Characterize the types of infections you might expect to see with defects of phagocyte function (6)

Answer 13

1) bacterial and fungal infections.
2) atypical or unusual infections
3) Catalase positive organisms in patients with CGD.
4) Infections of exceptional severity.
5) Peridontal disease in childhood.
6) Recurrent infections in areas of the body which interface with the microbial world.

Question 14

Characterize the types of infections you might expect to see with defects complement. (2)

Answer 14

1) Bacterial infections which might be seen with antibody deficiency (e.g., pyogenic organisms, H. influenzae, S. pneumoniae).
2) Terminal complement deficiencies (C5-C9) have problems with Neisseria organisms

Question 15

Discuss tests which would characterize a phagocyte problem. Differentiate between screening or confirmatory tests.

Answer 15

Screening:
• CBC, differential
• Review of morphology
• Bactericidal activity
• Chemotaxis assay
• Expression of CD11b/CD18
• NBT dye reduction or DHR oxidation.
Confirmatory/Detailed:
• Adherence to inert surface or endothelial cells. Measurement of CD11b/CD18, L-selection, Sialyl LeX.
• Response to chemoattractants: shape change, change in direction, rate of movement. Actin assembly.
• Ingestion of labeled particles or bacteria. Degranulation of specific and azurophilic components.
• Bactericidal/candidicidal activity. Production of O2-, H2O2 other oxidants.
• Studies for specific molecular defects in oxidase or other cell constituents.

Question 16

Discuss tests which would characterize a complement problem. Differentiate between screening or confirmatory tests.

Answer 16

Screening:
-C3, CH50
-Quantitative Ig’s, Lymphocyte numbers
Confirmatory/Detailed:
-Measurement of specific complement components: alternative and classical pathways.
-Detailed evaluation of adaptive immune response.

Question 17

Discuss management strategies for patients with innate immune disorders

Answer 17

1) Anticipation of infection and aggressive attempts to define the causative agent.
2) Surgical procedures for infected sites may be both diagnostic and therapeutic.
3) Prompt initiation of broad spectrum antibiotics covering a wide range of organisms, switching to specific coverage when microbial diagnosis is known.
4) For severe quantitative disorders of neutrophils, G-CSF may be used at a dose of 3 μg/kg/day to resolve the neutropenia (review from previous lecture).
5) Specific syndromes of neutrophil dysfunction may benefit from prophylactic antibiotics or cytokine therapy (e.g., INFγ for CGD).
6) Transplantation with hematopoietic stem cells has the capability to reconstitute neutrophil numbers and/or function.
7) Gene therapy: proof of concept studies has demonstrated reconstitution. Specific problems need to be resolved before a practical solution is achieved.