Allergic Diseases

Archive for May, 2008

Question: What two signals are required to activate naive T cells?

Sunday, May 18th, 2008

Answer: The first signal is provided by antigenic peptides displayed in MHC molecules. The second is provided by one or more costimulatory molecule produced by the antigen-presenting cell, in response to molecules displayed by pathogens. If these costimulatory signaling molecules are not present, the T cell-MHC interaction may alternatively cause the T cell to undergo […]

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Question: How does cell-mediated immunity work?

Saturday, May 17th, 2008

Answer: Cell-mediated immunity involves the action of T cells. CD8+ cytolytic T cells can kill target cells directly. CD4+ helper cells can activate macrophages to become more effective at killing the organisms they ingest. This process is also considered to be cell-mediated immunity, although, again, a cell of the innate system carries out the ultimate […]

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Question: How does humoral immunity work?

Friday, May 16th, 2008

Answer: Humoral immunity involves antibodies, produced by B cells. Terminally differentiated B cells, called plasma cells, produce most of the antibodies. Humoral immune responses defend the host against extracellular bacteria and toxins. Blocking antibodies can prevent the adherence of bacteria, viruses, or toxins to host cells. Antibodies can activate complement through the classical pathway and […]

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