Abstract
We recently reported a mouse model called ACE 10/10 in which macrophages overexpress the carboxypeptidase angiotensin-converting enzyme (ACE). These mice have an enhanced inflammatory response to tumors that markedly inhibits tumor growth. Here, we show that ACE modifies the C termini of peptides for presentation by major histocompatibility complex (MHC) class I molecules. The peptide-processing activity of ACE applies to antigens from either the extracellular environment (cross-presentation) or antigens produced endogenously. Consistent with its role in MHC class I antigen processing, ACE localizes to the endoplasmic reticulum. ACE overexpression does not appear to change the overall supply of peptides available to MHC class I molecules. The immunization of wild type mice previously given ACE 10/10 macrophages enhances the efficiency of antigen-specific CD8+ T cell priming. These data reveal that ACE is a dynamic participant in fashioning the peptide repertoire for MHC class I molecules by modifying the C termini of peptide precursors. Manipulation of peptidase expression by antigen-presenting cells may ultimately prove a useful strategy to enhance the immune response.
Highlights
Activity with substance P and LH-RH (2)
angiotensin-converting enzyme (ACE) 10/10 mice show several differences from wild type (WT) mice, a central hypothesis for their increased immune response is that the increased production of the peptidase ACE by MØ may enhance the presentation of major histocompatibility complex (MHC) class I-associated peptides to T cells
The studies presented here were undertaken after observing that ACE 10/10 mice respond to the intradermal implantation of melanoma with an enhanced inflammatory response, resulting in a marked reduction of tumor growth
Summary
Mice—ACE 10 mice have been described (10). Briefly, by gene targeting, the promoter region of the somatic ACE gene was substituted with the c-fms promoter, resulting in ACE overexpression in macrophage lineage cells. Cells and Cell Lines—Thioglycollate-elicited peritoneal exudate cells were collected via peritoneal lavage 4 days after a 2-ml injection of 3% thioglycollate broth intraperitoneally and were cultured in tissue culture-treated plates (1 ϫ 106/ml) at 37 °C and 5% CO2 in 10% fetal calf serum RPMI 1640, 50 M 2-ME, 0.5 mM sodium pyruvate, 10 mM HEPES buffer, 50 units/ml penicillin, 50 g/ml streptomycin, and 2 mM L-glutamine. Antigen-presenting Assay—In some experiments, antigenpulsed MØ or transfected L.Kb cells were stained with 25-D1.16 antibody. For the in vivo experiment presented, two groups of C57BL/6J recipients were transplanted intraperitoneally with 1.8 ϫ 107 thioglycollate-elicited peritoneal Mл from either ACE 10/10 mice or WT littermates. Cells were blocked with 1% bovine serum albumin and treated with rabbit anti-ACE serum. A secondary Alexa 546-labeled goat anti-rabbit antibody (Invitrogen) was used to stain ACE
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