O

T-cell receptor

MHC class I molecule presenting endogenous antigen

Effector T-cytotoxic cells do not recognize peptides presented by healthy "self" cell

Healthy "self" cell presents peptides from cytoplasmic proteins in the groove of MHC class I molecules

Effector T-cytotoxic cells do not recognize peptides presented by healthy "self" cell

Virus

Healthy "self" cell presents peptides from cytoplasmic proteins in the groove of MHC class I molecules

Virus

Virally infected "self" cell presents peptides from cytoplasmic proteins in the groove of MHC class I molecules

Effector T-cytotoxic cell recognizes viral peptides presented by infected "self" cell

Virally infected "self" cell presents peptides from cytoplasmic proteins in the groove of MHC class I molecules

Secretion of cytokines

Targeted delivery of cytotoxins that induce apoptosis

Virally infected "self" cell undergoes apoptosis

Secretion of cytokines

Targeted delivery of cytotoxins that induce apoptosis

Virally infected "self" cell undergoes apoptosis

Effector T-cytotoxic cell delivers preformed cytotoxins to the infected "self" cell and produces cytokines that allows neighboring cells to become more vigilant against intracellular pathogens

Figure 16.18 Consequences of Antigen Recognition by Effector T-Cytotoxic Cells of APCs include B cells and macrophages, both of which can gather and process extracellular antigen for presentation.

There appear to be two subsets of effector T-helper cells, Th1 and Th2, and these interact with different antigen-presenting cells. Th1 cells judge antigen presented by macrophages; if a Th1 cell recognizes a peptide displayed by a macrophage, it responds by activating that particular macrophage. In addition, Th1 cells are instrumental in orchestrating many aspects of the adaptive immune response. They release a wide variety of cytokines that induce proliferation of effector T cells, promote certain types of class switching by B cells, stimulate natural killer (NK) cells, increase production of monocytes in the bone marrow, recruit

16.7 T Lymphocytes: Antigen Recognition and Response 409

macrophages to the site, and cause changes in endothelial cells that allow phagocytic cells to adhere to and exit from the blood vessels. Th2 cells judge antigen presented by B cells; if a Th2 cell recognizes a peptide displayed by a B cell, it responds by activating that particular B cell. Th2 cells also support proliferation and most types of class switching by activated B cells.

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