Myelopoiesis
Phagocytes are specialized in destruction of foreign
materials; thus they have a fundamental role in body's
defense
against
invasion
by
micro-organisms,
destruction of tumor cells and ingestion of apoptotic
cells.
Phagocytes are classified into:
1.
polymorph nuclear: neutrophils, eosinophils and
basophils.
2.
mononuclear: monocytes and macrophages.
Neutrophils:
They are found in bone marrow, blood and
tissues.
They are the most numerous phagocytes as
normal range is 2.5-7.5 ×10
9
/L; constituting
about 65% of circulating leukocytes in man.
About 50% of neutrophils in blood marginate
to the wall of vessels and they are not
represented in blood count; demarginating in
response to infection, exercise and steroid
treatment.
Their half life in blood is short about 12-24
hours; after that they enter tissues where die
after 1-2 days.
They are easily identified in blood smear
when stained with Romanovsky stain by
characteristic segmented nucleus and pale
pink cytoplasm filled with indistinct violet
colored granules.
Neutrophilia:
It is a neutrophils count more than 7.5 ×10
9
/L; it's
causes are:
1.
Infection: e.g. bacterial.
2.
Inflammation: e.g. autoimmune diseases, gout and
tissue necrosis.
3.
Neoplasia: any malignancy.
4.
Metabolic conditions: e.g. uremia and acidosis.
5.
Hemorrhage and hemolysis.
6.
Corticosteroids.
7.
Bone marrow infiltration.
8.
Myeloproliferative disorders.
Neutropenia:
It is a neutrophils count less than 2 ×10
9
/L; it's causes
are:
1.
Racial.
2.
Congenital ( Kostman's syndrome ).
3.
Cyclical neutropenia.
4.
Hypoplastic
marrow;
paroxysmal
nocturnal
hemoglobinurea.
5.
Bone marrow infiltration.
6.
Megaloblastic anemia.
7.
Some acute infections: e.g. typhoid fever and
military TB.
8.
Drugs: e.g. anti-arrhythmic (amiodarone), anti-
convulsant (phenytoin).
9.
Exposure to radiation.
10.
Immune disorders: e.g. idiopathic, drugs, HIV
and infection.
11.
Hypersplenism.
Eosinophils:
They are minor type of granulocytes as normal
range is 0.04-0.4 ×10
9
/L constituting about 1-
4% of circulating leukocytes.
Their half life in blood is about 3-8 hours.
They are larger than neutrophils and
characterized by numerous large cytoplasmic
granules which stained deeply with acidic
dyes like eosin.
Causes of eosinophilia:
1.
Infection: e.g. parasitic.
2.
Inflammation: e.g. Polyarteritis nodosa.
3.
Allergy: e.g. atopy; drug sensitivity.
4.
Neoplasia: e.g. Hodgkin's and non-Hodgkin's
lymphomas
5.
Myeloproliferative disorders.
6.
Hyper-eosinophilic syndrome.
Basophils:
Their normal range is 0.01-0.1 ×10
9
/L
constituting about 0.2-1% of circulating
leukocytes.
Their half life in blood is about 2.5 days.
Mature basophils have multi-lobed nuclei and
contain numerous prominent granules which
stained purple with blue aniline dyes.
Causes of basophilia:
1.
Infection: pox virus.
2.
Inflammation:
3.
Metabolic conditions: e.g. Myxedema.
4.
Myeloproliferative disorders.
Monocytes:
Their normal range in blood is 0.2-0.8 ×10
9
/L
constituting
about
5%
of
circulating
leukocytes.
Their half life in blood is about 17 hours
They have a non-segmented nucleus of
variable shapes (round, oval, notched or
folded) with abundant grayish blue cytoplasm.
Causes of monocytosis:
1.
Infection: e.g. TB.
2.
Inflammation: e.g. systemic lupus erythematosus
and rheumatoid arthritis.
3.
Neoplasia: Chronic myelo-monocytic leukemia
(most common cause).
Lymphocytes:
There are 3 types of lymphocytes (T-cells, B-
cells and natural killer cells)
Their normal range in blood is 1-3 ×10
9
/L
constituting 20-40% of circulating leukocytes.
B- lymphocytes are the precursors of antibody
producing cells.
T- lymphocytes:
1.
provide signals inducing B- and T-cells
proliferation and differentiation.
2.
specifically delete virally infected cells
and foreign cells.
3.
act as effecter cells association with
macrophages.
4.
participate in the antigen-specific
selection of lymphocytes.
NK cells kill abnormal self and foreign cells
that fail to express on normal self class II MCH
on their surface.
Causes of lymphocytosis:
1.
Neoplasia: e.g. chronic lymphocytic leukemia,
lymphoma and hairy cells leukemia.
2.
Others:
Infection: Viral (HIV and mumps); Bacterial
(typhoid fever and pertusis); Protozoal
(toxoplasmosis).
Serum sickness.
Causes of lymphopenia:
1.
Infection: Influenza virus and septicemia.
2.
Lymphocytes loss as in lymphatic fistula.
3.
Drugs: e.g. anti-lymphocytes globulin (ALG).
4.
Neoplasia: e.g. metastatic carcinoma.
5.
Nutritional: e.g. folate and B 12 deficiency.
6.
Others: systemic lupus erythematosus.