Basophils in peripheral blood and bone marrow. A retrospective review

Behind the scenes with basophils: an emerging therapeutic target

Though basophils were originally viewed as redundant blood ‘mast cells’, the implementation of flow cytometry has established basophils as unique leukocytes with critical immunomodulatory functions. Basophils play an active role in allergic inflammation, autoimmunity, and hematological malignancies. They are distinguishable from other leukocytes by their characteristic metachromatic deep-purple cytoplasmic, round granules. Mature basophils are phenotypically characterized by surface expression of IL-3Rα (CD123); IL-3 drives basophil differentiation, degranulation, and synthesis of inflammatory mediators including type 2 cytokines. Basophil degranulation is the predominant source of histamine in peripheral blood, promoting allergic responses. Basophils serve as a bridge between innate and adaptive immunity by secreting IL-4 which supports eosinophil migration, monocyte differentiation into macrophages, B-cell activation, and CD4 T-cell differentiation into Th2 cells. Further, basophilia is a key phenomenon in myeloid neoplasms, especially chronic myeloid leukemia (CML) for which it is a diagnostic criterion. Increased circulating basophils, often with aberrant immunophenotype, have been detected in patients with CML and other myeloproliferative neoplasms (MPNs). The significance of basophils’ immunoregulatory functions in malignant and non-malignant diseases is an active area of research. Ongoing and future research can inform the development of immunotherapies that target basophils to impact allergic, autoimmune, and malignant disease states. This review article aims to provide an overview of basophil biology, identification strategies, and roles and dysregulation in diseases.

How I investigate basophilia in daily practice

Basophilia is a rare disorder of the complete blood count (CBC) and its management in daily practice remains unclear. Two main factors explain this situation. On the one hand, the reliability of the basophil count is insufficient, whether it is performed by a microscopic slide examination or by a hematology analyser. On the other hand, our knowledge of conditions associated with basophilia is largely based on few case reports and on reviews that refer to older reviews. The association between basophilia and myeloid neoplasm, especially chronic myeloid neoplasm, is well established. Conversely, there are conflicting data on some benign medical conditions and it remains unclear where basophilia may be present. In this review, we have investigated the medical literature to define which medical conditions can lead to basophilia and which cannot, and we propose a practical approach to manage basophilia divided into 3 steps. First, we have to check the real existence of the basophilia by getting rid of spurious basophilia. Then, we have to look for symptoms that suggest reactive basophilia and for clue of a neoplastic cause. Finally, in case of suspicion of a myeloid neoplasm or persistence of the basophilia in the absence of a reactive cause, we have to decide which examinations need to be prescribed to confirm a neoplastic basophilia.

De novo CD5+ diffuse large B cell lymphoma with basophilia in the peripheral blood: successful treatment with autologous peripheral blood stem cell transplantation

Basophils play an important role in allergic inflammation and are pathologically related to hematological disturbances, such as iron deficiency anemia and myeloproliferative disorders; however, they are only rarely encountered in lymphoid malignancies. Here, we report the case of a 33-year-old man with a bulky mass of the small intestine, multiple paraaortic lymphoadenopathy, pleural effusion, and ascites, who was diagnosed as a case of de novo CD5+ diffuse large B cell lymphoma (DLBCL). This patient showed a marked elevation of the basophil count in the peripheral blood, which appeared to run in parallel with the tumor burden. High dose chemotherapy followed by autologous peripheral blood cell transplantation yielded complete remission, and the patient has remained disease free for 5 years. To the best of our knowledge, this is the first report of a case of de novo CD5+ DLBCL showing marked elevation of the PB basophil count.

Transformation into acute basophilic leukaemia in a patient with myelodysplastic syndrome

We describe a patient with basophilic leukaemia following a 2-year period with myelodysplastic syndrome (refractory anaemia). The marrow showed 59.4% of blasts with 25.0% of mature and immature basophils. The leukaemic blasts contained granules, positively stained with toluidine blue but negative for peroxidase. The basophilic differentiation was confirmed by ultrastructural analysis demonstrating immature basophil granules. In addition, a morphological transition from immature blasts to more mature basophils was observed. Immunophenotypic analysis of blasts and basophils showed positive for CD5, CD7, CD13, CD33 and CD34. Cytogenetic investigation showed an abnormal karyotype, 46,XY,del(5)(q31q35), in 11% of the cells examined when the initial diagnosis of refractory anaemia was made. However, expansion of the same clone up to 100% was observed concomitantly with transformation to basophilic leukaemia.

Circulatory basophilia in guinea pigs with delayed-type hypersensitivity. Topical antigenic provocation induces circulatory basophilia

Circulatory basophilia could be induced in inbred guinea pigs systematically immunized with ovalbumin and consequently provoked repeatedly with dissolved ovalbumin applied onto the mucosa of the nares or the outer eye. The degree of the increase in circulatory basophil granulocytes depended on the adjuvant used and was significantly more pronounced after immunization with Freund's complete adjuvant than with alhydrogel (Al(OH)3). The degree of basophilia was also dependent on the animal strain, but different in two strains selected for high-asthma trait.

Hematologic manifestations of malignancy

Hematologic dysfunction occurs commonly in patients with malignancy. Over half are anemic, often because of acute or chronic blood loss, marrow involvement by the malignancy, marrow suppressive effects of chemotherapy or radiation therapy, or because of the anemia of chronic disease. Less frequently, anemia may result from red cell aplasia, folate or B12 deficiency, hemolytic processes, or hypersplenism. Occasional patients may become polycythemic because of erythropoietin-producing tumors such as renal adenocarcinomas or cerebellar hemangiomas. Elevation of the white cell count is commonly seen, especially in patients with lung cancer. Monocytosis and thrombocytosis, which may be early signs of an underlying malignancy, are also very common and occur in up to half of patients. Thrombocytopenia is commonly a result of therapy or marrow replacement; a few patients may have a syndrome resembling immune thrombocytopenic purpura. Abnormalities of coagulation are present in many patients, and may lead to superficial or deep venous thromboses, pulmonary emboli, nonbacterial thrombotic endocarditis with arterial emboli, bleeding, or acute disseminated intravascular coagulation. A sound understanding of the potential hematologic complications that can result from the malignant process is essential to the clinician caring for cancer patients.

Basophils in acute myeloid leukaemia

Thirty four out of 750 patients entered into the Medical Research Council's (MRC) 9th Acute Myeloid Leukaemia Trial had more than 1% basophils (range 1-27%) often with bizarre granulation and primitive forms, a rare finding in this disease. Both normal and abnormal karyotypes were present including abnormalities of 6p, 12p, and the Philadelphia chromosome. Basophilia was found in both "monolineage" and "multilineage" leukaemias and the commonest French-American-British (FAB) classification group was M2, followed by M4. Basophilia did not seem to be associated with a worse prognosis, although cases with abnormalities of 6p died of disease that was resistant to first line conventional chemotherapy.

Clinical interpretation of leukocyte responses

Basic information has been presented concerning leukocyte (neutrophil, monocyte, lymphocyte, eosinophil, and basophil) function, production, kinetics, and response to various physiological and disease states. Using this information, veterinary practitioners should be able to interpret leukogram data from sick and healthy dogs and cats. Specifically, characteristic leukogram patterns such as physiological leukocytosis, corticosteroid-associated changes, and the presence of infection or severe inflammation should be recognized. In addition, interpretation of individual leukocyte responses should be possible. Several tables have been provided to assist in constructing a differential diagnosis to explain increases or decreases in absolute leukocyte numbers that lie outside of expected reference intervals.

Translocations t(15;17) and t(9;14)(q34;q22) in a case of acute promyelocytic leukemia with increased number of basophils

A patient with a variant form of acute promyelocytic leukemia (M3 variant) associated with an increased number of basophils was found to present a reciprocal translocation, t(9;14)(q34;q22) in addition to t(15;17)(q22;q12). Although several cases of acute nonlymphocytic leukemia with increased bone marrow and peripheral blood basophils have been reported, this is the first case in which both the t(9;14) and basophilia were observed in a patient with M3. Our findings support the hypothesis that 9q34 may be associated with the chromosomal location of genes regulating the production and maturation of basophils.