ABSTRACTS: Oral Presentation Abstracts
Introduction: MHC class II positive late endosomes are suggested to be involved in antigen presentation by enterocytes to CD4+ T cells. Enterocytes of BALB/c but not of SCID mice facilitate ovalbumin trafficking into late endosomes. In this study the influence of IFN-gamma, known to induce antigen targeting to late endosomes in macrophages, as well as MHC class II proteins on the processes of antigen transport within enterocytes was analyzed in-vivo.
Methods: Subcellular targeting of ovalbumin was examined in enterocytes of SCID, IFN-gamma treated SCID, BALB/c and C57BL/6 class II knock out mice. Ovalbumin, lysosome-associated membrane protein-1 and MHC class II antigens were localized in jejunal specimens taken 0, 5, 10, 20 and 60 minutes after a single feed with ovalbumin by fluorescence and electron microscopy.
Results: Sorting of ovalbumin into late endosomes was found in enterocytes from BALB/c, C57BL/6 knock out and IFN-gamma stimulated SCID mice, but not from untreated SCID mice. MHC class II protein expression was restricted to enterocytes of IFN-gamma treated SCID and BALB/c mice, present at basolateral membranes and within endosomal compartments. Enterocytes of these mice further revealed colocalisations of class II antigens and ovalbumin in large endosomes. Delivery of ovalbumin into class II positive late endosomes of enterocytes occurred within 10 minutes after feeding.
Conclusion: Our data provide evidence of two transport mechanisms into late endosomes of which one is mediated by IFN-gamma possibly in conjugation with MHC class II proteins and another sorting process which occurs in the absence of MHC class II proteins.