Cellular localization of interleukin-5 expression in rectal carcinoma with eosinophilia

Eosinophilia often occurs in malignant diseases. This report concerns a female patient aged 76 years, diagnosed with rectal carcinoma with eosinophilia. Sera were obtained at two different periods (at diagnosis and after the operation) for the evaluation of levels of interleukin-5 (IL-5). The serum IL-5 level increased to 264 pg/mL, and returned to an undetectable level after the operation. The serum at diagnosis enhanced the viability of normal eosinophils in vitro, and this activity was inhibited by antihuman IL-5 polyclonal antibody. Immunohistochemistry and in situ hybridization revealed that stromal eosinophils contained IL-5 protein and messenger RNA (mRNA), but no IL-5 transcripts were detected in eosinophils attached to carcinoma cells. In situ detection of apoptosis showed that several eosinophils attached to tumor cells underwent apoptosis and lost their eosinophil secreted cationic protein (ECP) and major basic protein (MBP). These results may suggest that activated eosinophils by IL-5 play an important role in host defense mechanisms, releasing their toxic granule proteins on adjoining tumor cells.