THE EFFICIENCY OF ANTIGEN DELIVERY FROM MACROPHAGE PHAGOSOMES INTO CYTOPLASM FOR MHC CLASS I-RESTRICTED ANTIGEN PRESENTATION

Macrophages can present exogenous antigen in association with MHC clas s I molecules. Indirect evidence indicates that antigens internalized by phagocytosis can enter cytoplasm before following the conventional MHC class I presentation pathway. However, little is known about how c ommon such entry is, or to what extent it depends or? the h-ind of par ticle ingested. This study reports quantitative and morphological char acterization of antigen delivery from phagosomes into cytoplasm for MH C class I-restricted antigen presentation. Ovalbumin (OVA) was associa ted with polystyrene particles (PS), biodegradable poly-e-caprolactone particles (PCL), and sheep red blood cells (SRBC), and its delivery i nto macrophage cytoplasm via phagocytosis was assessed with a T hybrid oma assay for MHC class I-restricted presentation of OVA-derived pepti des. Although direct introduction of antigen into cytoplasm by scrape- lending produced the most efficient presentation, comparable signals c ould be obtained after phagocytosis of PCL or PS. Phagocytosis of OVA- loaded SRBC, and OVA internalized by pinocytosis, did not deliver effi ciently. MHC class I-restricted presentation of phagosome-derived OVA required cytoplasmic processing, as it was inhibited by proteasome inh ibitors and brefeldin A. Morphological studies showed that biotinylate d OVA originating in PCL phagosomes could be delivered into the cytopl asm of 90% of the macrophages, These results indicate that phagocytosi s per se is not sufficient to deliver antigen into cytoplasm, but that phagocytosis of solid, synthetic polymeric particles delivers antigen efficiently into cytoplasm for MHC class I processing. (C) 1997 Publi shed by Elsevier Science.