QUANTITATIVE DISORDERS OF EOSINOPHIL AND BASOPHIL
EOSINOPHILS
• Eosinophils are granulocytes that arise principally from the bone marrow and first described by Paul Ehrlich in 1879.
• Count: 2-5% or 0-0.04x 10^3/μl
• The half-life of eosinophils in the circulation is approximately 18 hours
• Size: 12 to 15 μm in diameter
• Cytoplasm contains coarse orang red granules and their nucleus are condensed, dark purple, usually bilobed, although three or more lobes are often observed.
• The eosinophil originates from the IL-5 responsive CD34+ myeloid progenitor cells (CFU-Eo).
• Cytokines that influence proliferation and differentiation of the eosinophil lineage include GM-CSF, IL-3, and IL-5.
• IL-5, released largely by activated TH lymphocytes and in small amounts by eosinophils, mast cells, NK cells, and natural killer T (NKT) cells.
EOSINOPHILIA
• Increase in the number of circulating eosinophils greater than >0.4×10^9/L is termed as eosinophilia.
• Clinically it is three types
a) mild eosinophilia (0.5 to 1.5 × 10^9/L),
b) moderate eosinophilia (1.5 to 5.0 × 10^9/L)
c) marked eosinophilia (>5.0 × 10^9/L)
Causes of Eosinophilia
• Non Clonal (Reactive) eosinophilia
• Reactive eosinophilia appears to be induced by cytokines secreted from T lymphocytes
• Various conditions associated with the cellular immune response (mediated by T lymphocytes) are characterized by eosinophilia
• Tissue-invasive parasites
• Allergic conditions in:
Respiratory tract disorders (Allergic Asthma)
Gastrointestinal diseases
Skin (dermatitis) and connective tissue disorders
• Tissue-invasive parasites
• Tissue invasion by parasites produces an eosinophilia more distinct than parasitic infestation of the gut or blood.
• Larvae are too large for phagocytosis so they readily adhere to larvae coated with IgG, IgE
• Intracellular eosinophilic granules fuse with the eosinophil membrane and expel their contents into the space between the cell and the larva.
• The granular substances attack the larva wall and destroy it.
• Clonal (Neoplastic) eosinophilia
• Primary or clonal eosinophilia is characterized by persistent eosinophilia > 1.5 x 10^9/L with tissue infiltration.
• It may be a clonal myeloid or lymphoid neoplastic disorder with mutations in genes that code for platelet derived growth factor receptor (PDGFR) or fibroblast growth factor receptor 1
• These disorders are considered myeloproliferative neoplasms.
• Idiopathic eosinophilia
• If cause for the eosinophilia is unknown and clonality cannot be demonstrated. These disorders are collectively known as idiopathic hypereosinophilic syndrome.
• Chronic persistent eosinophilia can cause extensive tissue damage as the granules are released from disintegrating eosinophils.
• In many HES cases, large numbers of circulating eosinophils damage the heart.
• Charcot-Leyden crystals formed from either eosinophil cytoplasm or granules can be found in exudates and tissues. Idiopathic HES must be differentiated from reactive eosinophilias and clonal eosinophilias.
• Eosinophilic leukemia usually presents with myeloblasts and eosinophilic myelocytes, whereas idiopathic HES and reactive eosinophilia present with mature eosinophils.
EOSINOPENIA
• Eosinophils lower limit of the reference range (0-0.04x 10^9/L) is very low, a decrease is difficult to determine and is probably not significant.
• Eosinopenia can be seen in acute infections, inflammatory reactions and with the administration of glucocorticosteroids.
• Glucocorticosteroids and epinephrine inhibit eosinophil release from the bone marrow and increase their margination
BASOPHILS
• Basophils are granulocytes that arise from the CD34+ myeloid progenitors in the bone marrow.
• IL-3 is the main cytokine involved in human basophil growth and differentiation, but GM-CSF, stem cell factor (SCF), IL-4, and IL-5 can also be involved.
• Count: <1 % or < 0.2 x 10^3/μl
• Size: Basophil 10 to 15 μm and mast cell 20 μm in diameter
• Cytoplasm contains large size, dark blue or blackish granules and their nucleus are condensed, dark purple, usually bilobed.
Both basophils and mast cells are important in inflammatory and immediate allergic reactions because they are both able to release inflammatory mediators.
image
BASOPHILIA
• Basophilia refers to an increase in basophils >0.2 10^9/L.
• It is associated with immediate hypersensitivity reactions and chronic myeloproliferative disorders.
• An absolute basophilia is often helpful in distinguishing CML from a leukemoid reaction.
• Basophil count >80% of the total leukocyte with absence of the Philadelphia chromosome
(BCR/ABL1 translocation) suggests the diagnosis of acute basophilic leukemia.
DECREASE BASOPHIL COUNT
• A decrease in basophils is even more difficult to establish and decreases in numbers are seen in inflammatory states and following immunologic reactions.
• MASTOCYTOSIS: Increased number of mast cell fourfold in tissue and that affected tissues (most commonly the skin) and in conjunction with certain neoplastic disorders.
• No clinical disorder that involves a decrease in mast cells numbers has been identified; however, long-term treatment with glucocorticoids can lower the number of mast cells.
