Polymorphonuclear neutrophils and granulocytic myeloid-derived suppressor cells inhibit natural killer cell activity toward Aspergillus fumigatus.

Invasive aspergillosis is a devastating infectious disease in immunocompromised patients. Besides neutrophils and macrophages, natural killer (NK) cells have recently emerged as important players in immunity to this infection. It was shown that NK cells comprise an essential role in the clearance of Aspergillus fumigatus (A. fumigatus) in neutropenic but not in nonneutropenic mice. However, the antifungal activity of NK cells and their regulation have not been fully characterized. In this study, we investigated the interplay between polymorphonuclear neutrophils (PMNs) or granulocyte myeloid-derived suppressor cells (Gr-MDSCs) with NK cells. Both cell types exhibited an equal inhibitory effect on NK cell activation through downregulation of NKp30 expression on the cell surface and cytotoxicity towards the cell line K562. Furthermore, we showed that NK cell activation and antifungal cytotoxicity were impaired when NK cells had been cultured in the presence of PMNs or Gr-MDSCs before fungal stimulation. Besides the reduced cytotoxicity a decreased release of interferon gamma (IFNγ), a key player in the clearance of an A. fumigatus infection, was observed. Thus, inhibition of NK cell activity by PMNs or Gr-MDSCs might impair an effective anti-fungal immune response during recovery from conditions such as hematopoietic stem cell transplantation.

Establishment of a mammary carcinoma cell line from Syrian hamsters treated with N-methyl-N-nitrosourea.

Clearly new breast cancer models are necessary in developing novel therapies. To address this challenge, we examined mammary tumor formation in the Syrian hamster using the chemical carcinogen N-methyl-N-nitrosourea (MNU). A single 50mg/kg intraperitoneal dose of MNU resulted in a 60% incidence of premalignant mammary lesions, and a 20% incidence of mammary adenocarcinomas. Two cell lines, HMAM4A and HMAM4B, were derived from one of the primary mammary tumors induced by MNU. The morphology of the primary tumor was similar to a high-grade poorly differentiated adenocarcinoma in human breast cancer. The primary tumor stained positively for both HER-2/neu and pancytokeratin, and negatively for both cytokeratin 5/6 and p63. When the HMAM4B cell line was implanted subcutaneously into syngeneic female hamsters, tumors grew at a take rate of 50%. A tumor derived from HMAM4B cells implanted into a syngeneic hamster was further propagated in vitro as a stable cell line HMAM5. The HMAM5 cells grew in female syngeneic hamsters with a 70% take rate of tumor formation. These cells proliferate in vitro, form colonies in soft agar, and are aneuploid with a modal chromosomal number of 74 (the normal chromosome number for Syrian hamster is 44). To determine responsiveness to the estrogen receptor (ER), a cell proliferation assay was examined using increasing concentrations of tamoxifen. Both HMAM5 and human MCF-7 (ER positive) cells showed a similar decrease at 24h. However, MDA-MB-231 (ER negative) cells were relatively insensitive to any decrease in proliferation from tamoxifen treatment. These results suggest that the HMAM5 cell line was likely derived from a luminal B subtype of mammary tumor. These results also represent characterization of the first mammary tumor cell line available from the Syrian hamster. The HMAM5 cell line is likely to be useful as an immunocompetent model for human breast cancer in developing novel therapies.