Expression Of K～b-EGFP In RAW246.7 And The Function Of The Recombinant K～b During Cross-presentation

T lymphocytes recognize antigenic peptide fragments presented by major histocompatibility complex(MHC) class I or class II molecules. For MHC class I, classical antigen presentation studies suggest that proteins synthesized within cytosol are processed into peptides by means of a multicatalytic protease know as the proteasome. The antigenic peptides enter the lumen of the endoplasmic reticulum(ER) aided by the TAP proteins, after which they bind nascent MHC class I. The assembled class I-peptide complexes are subsequently transpoted from ER to the Golgi complex and the plasma membrane for interaction with CD8+T cells. In contrast, MHC class II molecules present antigens captured from the environment. The exogenous proteins are internalized by phagocytosis or macropinocytosis into the endocytic system, where they are degraded by acid-optimal proteases and presented to CD4+T cells by MHC class II molecules that accumulate in the late endosomal and lysosomal compartments.An exception to this rule was noted 26 years ago, and it was suggested initially that host antigen-presenting cells(APCs) prime CD8+T cell responses against minor histocompatibility antigens of foreign donor cells. Now this process is called cross- presentation. Increasing evidence suggests that this presentation pathway is involved in a wide vatiety of CD8+T cell responses to different exogenous antigens. The capacity of professional APC to present exogenous antigens in the MHC class I pathway may be an obligatory mechanism in eliminating virus that can't infect APCs and some tumors. Therefore, it is important to elucidate the cellular and molecular mechanisms underlying the cross-presentation pathway.Two fundamentally distinct routes have been described as contributing to exogenous antigen presentation by MHC class I molecules. One is involved in the access of exogenous antigen to the cytosol by a possible membrane rupture of the endosome or by a selective transport mechanism. In this route, antigen was processed and presented via the classical...