McGarry, Michael P.

AbstractThe identification and characterization of mouse basophils have historically been hampered by the extreme rarity of this cell type. Virtually no photomicrographs of hematologically stained (eg, Wright-Giemsa) examples of mouse basophils exist in the literature. However, 4 recent studies in the past 2 years have used flow cytometry and a defined set of cell-surface markers to identify and subsequently isolate mouse “basophils,” including the publication of stained cytospin preparations of these cells. Surprisingly, a reevaluation of the data from all 4 of the studies revealed several issues of concern that suggest that the cells under study are not necessarily basophils. Nonetheless, we propose that these studies do provide the foundation for a reevaluation of the defining characteristics of a basophil and/or provide support for the provocative conclusion that a new previously overlooked leukocyte subtype has been identified. The purpose of this commentary is to revisit these previously published studies, highlight the relevant issues, and provide a different perspective in the hope of developing a consensus within the research community as to the true identity of the “basophils” described in these studies.

Abstract Tumor-associated eosinophilia has been observed in numerous human cancers and several tumor models in animals; however, the details surrounding this eosinophilia remain largely undefined and anecdotal. We used a B16-F10 melanoma cell injection model to demonstrate that eosinophil infiltration of tumors occurred from the earliest palpable stages with significant accumulations only in the necrotic and capsule regions. Furthermore, the presence of diffuse extracellular matrix staining for eosinophil major basic protein was restricted to the necrotic areas of tumors, indicating that eosinophil degranulation was limited to this region. Antibody-mediated depletion of CD4+ T cells and adoptive transfer of eosinophils suggested, respectively, that the accumulation of eosinophils is not associated with T helper cell type 2-dependent immune responses and that recruitment is a dynamic, ongoing process, occurring throughout tumor growth. Ex vivo migration studies have identified what appears to be a novel chemotactic factor(s) released by stressed/dying melanoma cells, suggesting that the accumulation of eosinophils in tumors occurs, in part, through a unique mechanism dependent on a signal(s) released from areas of necrosis. Collectively, these studies demonstrate that the infiltration of tumors by eosinophils is an early and persistent response that is spatial-restricted. It is more important that these data also show that the mechanism(s) that elicit this host response occur, independent of immune surveillance, suggesting that eosinophils are part of an early inflammatory reaction at the site of tumorigenesis.

Eosinophils are often dominant inflammatory cells present in the lungs of asthma patients. Nonetheless, the role of these leukocytes remains poorly understood. We have created a transgenic line of mice (PHIL) that are specifically devoid of eosinophils, but otherwise have a full complement of hematopoietically derived cells. Allergen challenge of PHIL mice demonstrated that eosinophils were required for pulmonary mucus accumulation and the airway hyperresponsiveness associated with asthma. The development of an eosinophil-less mouse now permits an unambiguous assessment of a number of human diseases that have been linked to this granulocyte, including allergic diseases, parasite infections, and tumorigenesis.

AbstractThe ashen (ash) mouse, a model for Hermansky-Pudlak syndrome (HPS) and for a subset of patients with Griscelli syndrome, presents with hypopigmentation, prolonged bleeding times, and platelet storage pool deficiency due to a mutation which abrogates expression of the Rab27a protein. Platelets of mice with the ashen mutation on the C3H/HeSnJ inbred strain background have greatly reduced amounts of dense granule components such as serotonin and adenine nucleotides though near-normal numbers of dense granules as enumerated by the dense granule-specific fluorescent dye mepacrine. Thus, essentially normal numbers of platelet dense granules are produced but the granule interiors are abnormal. Collagen-mediated aggregation of mutant platelets is significantly depressed. No abnormalities in the concentrations or secretory rates of 2 other major platelet granules, lysosomes and alpha granules, were apparent. Similarly, no platelet ultrastructural alterations other than those involving dense granules were detected. Therefore, Rab27a regulates the synthesis and secretion of only one major platelet organelle, the dense granule. There were likewise no mutant effects on levels or secretion of lysosomal enzymes of several other tissues. Together with other recent analyses of the ashen mouse, these results suggest a close relationship between platelet dense granules, melanosomes of melanocytes and secretory lysosomes of cytotoxic T lymphocytes, all mediated by Rab27a. Surprisingly, the effects of the ashen mutation on platelet-dense granule components, platelet aggregation, and bleeding times were highly dependent on genetic background. This suggests that bleeding tendencies may likewise vary among patients with Griscelli syndrome and HPS with Rab27a mutations.

We have generated transgenic mice that constitutively express murine interleukin (IL)-5 in the lung epithelium. Airway expression of this cytokine resulted in a dramatic accumulation of peribronchial eosinophils and striking pathologic changes including the expansion of bronchusassociated lymphoid tissue (BALT), goblet cell hyperplasia, epithelial hypertrophy, and focal collagen deposition. These changes were also accompanied by eosinophil infiltration of the airway lumen. In addition, transgenic animals displayed airway hyperresponsiveness to methacholine in the absence of aerosolized antigen challenge. These findings demonstrate that lung-specific IL-5 expression can induce pathologic changes characteristic of asthma and may provide useful models to evaluate the efficacy of potential respiratory disease therapies or pharmaceuticals.