Monocytosis: a new observation during radiotherapy

Differential Diagnosis and Workup of Monocytosis: A Systematic Approach to a Common Hematologic Finding

Purpose of Review

Monocytosis is a frequently encountered clinical condition that needs appropriate investigation due to a broad range of differential diagnoses. This review is meant to summarize the latest literature in the diagnostic testing and interpretation and offer a stepwise diagnostic approach for a patient presenting with monocytosis.

Recent Findings

Basic studies have highlighted the phenotypic and functional heterogeneity in the monocyte compartment. Studies, both translational and clinical, have provided insights into why monocytosis occurs and how to distinguish the different etiologies. Flow cytometry studies have illustrated that monocyte repartitioning can distinguish chronic myelomonocytic leukemia, a prototypical neoplasm with monocytosis from other reactive or neoplastic causes.

Summary

In summary, we provide an algorithmic approach to the diagnosis of a patient presenting with monocytosis and expect this document to serve as a reference guide for clinicians.

Non-myeloablative busulfan chimeric mouse models are less pro-inflammatory than head-shielded irradiation for studying immune cell interactions in brain tumours

Background

Chimeric mouse models generated via adoptive bone marrow transfer are the foundation for immune cell tracking in neuroinflammation. Chimeras that exhibit low chimerism levels, blood-brain barrier disruption and pro-inflammatory effects prior to the progression of the pathological phenotype, make it difficult to distinguish the role of immune cells in neuroinflammatory conditions. Head-shielded irradiation overcomes many of the issues described and replaces the recipient bone marrow system with donor haematopoietic cells expressing a reporter gene or different pan-leukocyte antigen, whilst leaving the blood-brain barrier intact. However, our previous work with full body irradiation suggests that this may generate a pro-inflammatory peripheral environment which could impact on the brain’s immune microenvironment. Our aim was to compare non-myeloablative busulfan conditioning against head-shielded irradiation bone marrow chimeras prior to implantation of glioblastoma, a malignant brain tumour with a pro-inflammatory phenotype.

Methods

Recipient wild-type/CD45.1 mice received non-myeloablative busulfan conditioning (25 mg/kg), full intensity head-shielded irradiation, full intensity busulfan conditioning (125 mg/kg) prior to transplant with whole bone marrow from CD45.2 donors and were compared against untransplanted controls. Half the mice from each group were orthotopically implanted with syngeneic GL-261 glioblastoma cells. We assessed peripheral blood, bone marrow and spleen chimerism, multi-organ pro-inflammatory cytokine profiles at 12 weeks and brain chimerism and immune cell infiltration by whole brain flow cytometry before and after implantation of glioblastoma at 12 and 14 weeks respectively.

Results

Both non-myeloablative conditioning and head-shielded irradiation achieve equivalent blood and spleen chimerism of approximately 80%, although bone marrow engraftment is higher in the head-shielded irradiation group and highest in the fully conditioned group. Head-shielded irradiation stimulated pro-inflammatory cytokines in the blood and spleen but not in the brain, suggesting a systemic response to irradiation, whilst non-myeloablative conditioning showed no cytokine elevation. Non-myeloablative conditioning achieved higher donor chimerism in the brain after glioblastoma implantation than head-shielded irradiation with an altered immune cell profile.

Conclusion

Our data suggest that non-myeloablative conditioning generates a more homeostatic peripheral inflammatory environment than head-shielded irradiation to allow a more consistent evaluation of immune cells in glioblastoma and can be used to investigate the roles of peripheral immune cells and bone marrow-derived subsets in other neurological diseases.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1410-y) contains supplementary material, which is available to authorized users.

How I investigate monocytosis

Monocytosis is a common finding that is caused by a wide variety of neoplastic and non-neoplastic conditions. The adequate evaluation of monocytosis involves the integration of laboratory data, morphology, clinical findings, and the judicious use of ancillary studies. We review the literature on monocytosis, including the 2017 revised 4th edition of the World Health Organization classification of hematopoietic neoplasms. We present a review of monocytosis with practical guidelines on how to approach both routine and challenging cases.

Radiation sensitivity of human and murine peripheral blood lymphocytes, stem and progenitor cells

Immunodeficiency is a severe side effect of radiation therapy, notably at high radiation doses. It may also impact healthy individuals exposed to environmental ionizing radiation. Although it is believed to result from cytotoxicity of bone marrow cells and of immunocompetent cells in the peripheral blood, the response of distinct bone marrow and blood cell subpopulations following exposure to ionizing radiation is not yet fully explored. In this review, we aim to compile the knowledge on radiation sensitivity of immunocompetent cells and to summarize data from bone marrow and peripheral blood cells derived from mouse and human origin. In addition, we address the radiation response of blood stem and progenitor cells. The data indicate that stem cells, T helper cells, cytotoxic T cells, monocytes, neutrophils and, at a high degree, B cells display a radiation sensitive phenotype while regulatory T cells, macrophages, dendritic cells and natural killer cells appear to be more radioresistant. No conclusive data are available for basophil and eosinophil granulocytes. Erythrocytes and thrombocytes, but not their precursors, seem to be highly radioresistant. Overall, the data indicate considerable differences in radiosensitivity of bone marrow and blood normal and malignant cell populations, which are discussed in the light of differential radiation responses resulting in hematotoxicity and related clinical implications.

Human monocytes and lymphocytes differ in the rate of DNA repair synthesis and viability after exposure to nitrogen mustard

Unscheduled DNA synthesis was studied in human lymphocytes and monocytes after treatment with nitrogen mustard, methyl-methane-sulphonate and ultraviolet irradiation. The unscheduled DNA synthesis was about 4 times higher in monocytes than in lymphocytes after treatment with nitrogen mustard. Treatment with methyl-methane-sulphonate or ultraviolet irradiation confirmed the higher capacity for unscheduled DNA synthesis in the monocytes. When Ficoll-Isopaque-isolated mononuclear cells were exposed to various doses of nitrogen mustard and incubated for different periods, a dose- and time-dependent increase in trypan blue uptake was found. Furthermore, a corresponding dose- and time-dependent decrease was noted in 3H-uridine incorporation. Since trypan blue uptake will not enable differentiation between monocytes and lymphocytes appearing as a mixed cell population, 3H-uridine flash labeling index was studied after exposure to nitrogen mustard. There was a dose- and time-dependent decrease in 3H-uridine labeling index, suggesting a correlation between the absence of 3H-uridine incorporation and increase in trypan blue uptake. When compared to monocytes, the lymphocytes were more affected in this respect after exposure to nitrogen mustard. The possibility that differences in cytotoxic effect may be related to DNA repair mechanisms is discussed.

Long-term effects on the immune system following local radiation therapy for breast cancer. 4. Proliferative responses and induction of suppressor activity of the blood lymphocyte population

The long-term effect of local irradiation for breast cancer on the blood lymphocyte population was examined in 149 women who had been disease-free for 5-6 and 10-11 years. The patients were included in a clinical trial aiming at determining the value of pre- and post-operative irradiation (45 Gy) compared to surgery only. It was observed that the relative mitogen responses of lymphocytes to phytohaemagglutinin (PHA) and Concanavalin (Con A) and in a mixed lymphocyte culture (MLC) were significantly lower in irradiated compared to unirradiated patients at least a decade after treatment. The prolonged reductions of mitogen responses after irradiation could partly be due to an increased proportion of lymphocytes which may express suppressor function since the Con A-inducible suppressor activity of lymphocytes was significantly higher in irradiated compared to unirradiated patients.

Impaired B lymphocyte reactivity in patients after radiotherapy

The effect of therapeutic irradiation upon B lymphocyte function was investigated in patients with various malignancies. The test system used was a reverse hemolytic plaque assay, which made it possible to study the activation and differentiation of B lymphocytes into immunoglobulin-secreting cells (ISC). Peripheral blood lymphocytes from normal individuals and patients before and after radiotherapy were stimulated in vitro with the polyclonal B cell activator pokeweed mitogen, and the number of ISC was estimated. B cell reactivity was markedly reduced in those patients who had received irradiation within the last six months. In patients in whom radiotherapy had been terminated more than 12 months before the lymphocytes were tested, B cell reactivity was comparable to that of patients prior to radiotherapy. By means of marker analyses, there was a reduction of B lymphocytes and T lymphocytes in the peripheral blood with a preponderance of T helper cells. Several mechanisms--e.g., reduced or defective B cell differentiation, altered regulatory T-helper or suppressor cell function or activation of suppressive monocytes--could be responsible for impaired B cell reactivity after radiotherapy.

The effects of conventionally fractionated, extended portal radiotherapy on the human peripheral blood count

Conventionally fractionated, extended portal radiotherapy (CFEPRT) has been used to treat two diseases in which there was no marrow infiltration (viz. Hodgkin's disease and medulloblastoma). Blood count indices have been monitored during therapy and in the recovery phase. The lymphocytes were the most sensitive and the monocytes the most refractory leucocytes to change; the monocyte count tended to recover during CFEPRT. The platelet count fell gradually and soon after the neutrophil count. The nadir counts for white cells and platelets occurred early or toward the middle of CFEPRT, after which levels were maintained. The hemoglobin slightly and progressively declined. The patterns of change were similar for the two portals analyzed. Absolute eosinophilia occurred in 9 of the 53 CFEPRT patients, often in the recovery period. All patients who maintained their early nadir levels throughout the rest of the CFEPRT demonstrated fast recovery of all indices following completion of radiotherapy; the lymphocyte count recovered fastest. Recent prior CFEPRT or standard MVPP (nitrogen mustard, vinblastine, procarbazine, prednisolone) chemotherapy rendered the blood count more liable to radiation induced cytopenia. A lapse of more than 3 months between MVPP and CFEPRT allowed greater tolerance to the radiotherapy. Recent MVPP may be less myelosuppressive than recent mantle radiotherapy with respect to subsequent tolerance to CFEPRT.