Previous studies have shown that eosinophils accumulate within many epithelial tumors. Nonetheless, the basis of this accumulation or the specific localization of eosinophils within these tumors remains obscure.

C57BL/6J mice were injected (s.c.) with B16 melanoma cells and tumors harvested at days 10 and 16 for immunohistochemistry using antibodies to eosinophil major basic protein (MBP). Additional groups of tumor bearing mice were examined, including recipients of adoptively transferred eosinophils, and mice administered mAbs to deplete CD4⁺ T-cells and eosinophils.

Eosinophils accumulate differentially in tumors, occurring in the necrotic and capsule areas and noticeably absent from viable regions. Interestingly, necrotic areas appeared in tumors of mice devoid of eosinophils. This accumulation was an active process as adoptively transferred (i.v.) eosinophils were recruited to necrotic areas within 24 hours of transfer. Transwell chemotaxis assays failed to detect tumor cell-released chemoattractants. Despite an association with Th2 responses, eosinophil accumulation also occurred in mice devoid of CD4⁺ T cells.

Eosinophils are actively recruited to solid tumors and differentially accumulate in the necrotic and capsule areas independent of Th2 responses (i.e., in the absence of CD4⁺ T cells). In the absence of released chemoattractants and a direct link between eosinophils and tumor cell death, the mechanism(s) and consequence(s) of this accumulation is unclear.