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Background: IL-33, a recently described member of the IL-1-family, is an important player in a variety of inflammatory settings and is thought to be released from damaged or necrotic cells. Little work has so far been published on the cellular expression and regulation of IL-33 in inflammatory lesions. Results: In normal mouse skin IL-33 showed a nuclear expression in non-proliferating keratinocytes (Ki67-) and periglandular myoepithelial cells. After injection with Staphylococcus aureus (6h i.d.) we observed that nuclear IL-33 disappeared from keratinocytes in the center of the lesion and instead appeared in fibroblasts at the periphery. The keratinocyte layer remained intact and expressed nuclear HMGB1, revealing no evidence of overt necrosis at this time point, thus indicating possible secretion. Wound lesions of the ear showed a similar picture at the margins. At later time points IL-33 reappeared in keratinocytes, initially in a hyperproliferative, multilayer structure in which IL33 and Ki-67 remained minimally co-localized. Similarly, in cultured human keratinocytes there was constitutive expression of nuclear IL-33 in non-proliferating cells and in contrast to endothelial cells, expression levels appeared unaffected by cell density or pro-inflammatory activation (TNF-a or IL1b) Conclusion: The regulation of IL-33 in keratinocytes appears to involve molecular signals different from the regulation seen in vascular endothelial cells and deserves further investigation.

Background: MHC class II-restricted CD4+ T cells reactive against the Id peptide of MHC class II-negative MOPC315 murine myeloma cells can protect mice against injected tumors. This protection occurs via indirect recognition of secreted tumor-specific antigen, presented on MHC class II-molecules of tumor-infiltrating CD11b+ cells. Activated Id-specific Th1 cells produce IFNγ that activate macrophages which become cytotoxic to tumor cells. We wanted to assay the ability of such CD4+/M1 macrophage mediated protection to prevent the outgrowth of antigen-loss tumor variants. Methods: Id-specific TCR-transgenic SCID mice were challenged with a mixed population of Id-secreting and non-secreting MOPC315 cells, differentially labeled with fluorescent proteins. Tumor growth was monitored by in vivo imaging. Tumor-infiltrating macrophages were assayed for their ability to inhibit tumor growth. Results: In the presence of a large excess of antigen-secreting tumor cells, outgrowth of antigen loss-variants occurred with no evidence of bystander killing. A predominance of alternatively activated macrophages was seen in areas dominated by antigen loss-variants, whereas classic activation was the dominant phenotype in areas populated by regressing Id-secreting tumor cells. In vitro, growth of antigen loss-variants was completely inhibited by the provision of the tumor-specific antigen. This data suggests strict spatial requirements of antigen for effective macrophage-mediated protection.