It may be related to the conversion of ALA into heme, as suggested by a previous study that exogenous ALA processing promotes heme efflux from intact developing cucumber chloroplasts and translates it into hemoglobin (Thoms and Weinstein 1990).
For instance, the CD8+ DEC205+ subset of murine splenic DC is more biased for cross-presentation on MHC class I molecules, whereas the CD8− DCIR2+ DC subset is specialized for MHC class II antigen presentation and displays increased expression of proteins involved in the exogenous antigen processing pathway, including cathepsins C, H, Z, and AEP.
Additionally, APCs are capable of internalising and processing exogenous antigens from neighbouring apoptotic cells that have been transfected.
Thus, we pose that an exogenous pathway for processing bacterial-derived antigens to prime CD8 T cell responses would indeed be required; however, this has not been directly addressed.
Thus, the pH of DC Listeria-containing phagosomes may influence the timing of bacterial escape and also contribute to the exogenous route of processing following direct infection with Listeria.
Highly ordered fibril-forming collagens produce second-harmonic generation (SHG) signals without the need for any exogenous label or processing, which correlate with the density and organization of the collagen matrix (Palero et al., 2007; Abraham et al., 2010).
Although in some studies murine pDCs fail to induce functional CD8+ T cells [ 18, 32], human pDCs appear to be competent in processing exogenous antigens to be presented in MHC class I molecules [ 33– 35] (Fig. 1).
Harding, C. V. & Song, R. Phagocytic processing of exogenous particulate antigens by macrophages for presentation by class I MHC molecules.
In fact, such similarity between human and non-human species may reveal a common basis of low level processing of exogenous rhythmic sequences.
