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Unformatted text preview: Messenger RNA (mRNA) Primary RNA transcript Rearranged DNA DJ rearrangement occurs first- Random process V- DJ rearrangement occurs next- Random process **B cells always make the heavy chain first Error in Pre-T cell Checkpoint- CD3 not expressed- Cell dies Mutation of RAG genes cause impaired rearrangement infected cell in the phagosome on MHC Class II and can activate T helper cells because it has a costimulatory signal hat escape the phagosome and go into the cytosol of the dendritic cell are expressed on MHC Class I and recognized by CTLs This cell does not have a costimulatory signal, thus it cannot activate CTLs 3d interaction with CR2 provides second signal for B cell activation 1 Immunology Test II Study Guide How Do Peptide Antigens Become Generated By APCs- Class II MHC molecules are recognized by T helper cells (CD4)- Class I MHC molecules are recognized by CTLs (CD8) Class I associated peptides are presented by nearly every nucleated cell in the body Class II associated peptides are presented by dendritic cells, B cells, macrophages- CTLs respond to antigen on Class I MHC by killing the presenting cell- T helper cells respond to antigen on Class II MHC by telling the APC how to eliminate the antigen- Class I-associated peptides are produced in the cytoplasm of an infected cell cytosolic peptides- Class II-associated peptides are derived from extracellular proteins in the blood, lymph, interstitial fluid that are brought into the APC by endocytosis. The peptide is then attached to class II MHCs in a vesicle and the MHC-peptide complex is placed on the cell surface of the APC Remember- Lets say Nave Guy who becomes infected bacteria have taken up residence in his arm and they are extracellular o Macrophages in the area have Toll-like receptors (TLRs) that recognize microbial products (PAMPS) , these receptors are non antigen-specific and the macrophage will endocytose the microbe o Dendritic cells in the area will also phagocytose the bacteria and migrate to the lymph nodes- In the lymph node, resides mature, nave B and T cells that are antigen-specific o Dendritic cells present peptide antigens to the nave T lymphocytes on an MHC Class II moleculeand multiple different peptide antigens are being presented simultaneously by that single dendritic cell o Therefore, because nave T cells only recognize one type of peptide antigen bound to an MHC, dendritic cells can present antigens to multiple T cells at the same time o Nave T helper cells 1) Recognizes peptide-MHC complex ( Recognition ) 2) Becomes an effector T helper cell ( Activation ) 3) Leaves lymph node and travels to site of infection o At the site of the infection, the macrophage presents the antigen to the effector T cell a second time, and Effector T helper cell sends signals to the macrophage to help it kill the pathogen it has engulfed o Also at the site of infection, there is some intact bacterial antigen that floats around and is...
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- Spring '10