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distribution – class Ⅱ molecules are expressed on ? B cells ? Mφ ? Dendritic cells ? Vascular endothelial cells 3. Functions i. Antigen processing and presenting (exogeneous pathway): – both pathogens in cellular vesicles and those e from outside the cell are presented on MHC class Ⅱ molecules of APCs and are transported to the cell surface where they can be recognized by CD4 + T cell ii. Involve in transplant rejection iii. Regulation of immune response iv. T cell development in the thymus C. Nonclassical HLA – (HLAⅠ b) 1. Differentiation or activation states 2. Disease 3. Cytokines IV. Factors influencing the expression of HLA molecules ( 1)內(nèi)源性抗原提呈:抗原 ? 靶細(xì)胞 ? 組成 HLAⅠ 類分子 抗原肽復(fù)合物 ? 表達(dá)于細(xì)胞膜表面 ? CD8+T細(xì)胞識別。 ( 2)外源性抗原提呈: 抗原 ? APC ?HLAⅡ 類分子 抗原肽復(fù)合物 ? 表達(dá)于細(xì)胞膜表面 ? CD4+T細(xì)胞識別 。 HLA與疾病的關(guān)系 (一) (relative risk,相對危險(xiǎn)率 ) 。 (二)舉例 B27 ( IDDM)與 DR DR4 病人( Ag+/Ag) 對照( Ag+/Ag) = VI. Significance of MHC 1. Control of immune response ? MHC restriction: – The ability of T lymphocytes to respond only when they are presen