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Immune System for AP Biology (page 3)

By — McGraw-Hill Professional
Updated on Oct 24, 2011

Well, this is too good to be true … we just got word that this body was just recently infected by a virus. This will allow us to look at the other side of the immune response: cell-mediated immunity. This type of immunity involves direct cellular response to invasion as opposed to antibody-based defense. The virus that infected this poor sap made it past the humoral immunity system because it entered into the host's cells. This brings the cytotoxic T cells into play. The cells infected by the virus are forced to produce viral antigens, some of which show up on the surface of the cell. The cytotoxic T cells recognize these cells and wipe them out.

You might wonder how these T cells avoid killing all cells. All the cells of the body, except for red blood cells, have on their surface antigens called class I histocompatability antigens (major histocompatibility complex [MHC]). The MHC I antigens for each person are slightly different, and the immune system accepts as friendly any cell that has the identical match for this antigen. Anything with a different MHC is foreign. This is the reason that organ donation often fails—the donor and the recipient have incompatible MHCs. There are also class II histocompatibility antigens, which are found on the surface of the immune cells of the body. These antigens play a role in the interaction between the cells of the immune system.

Well, I'd like to thank you for joining us on our tour of the body. We've seen a lot of things today and—whoa! We've been hit by something—and hit hard! Oh, dear…. Folks, I don't want you to be alarmed, but it appears that our rival tour company has played a bit of a practical joke on us. Apparently as we were observing the B cell's interaction with the vaccine, they attached a series of antigens and complement proteins to the surface of our bus. That loud noise you just heard was the sound of a macrophage taking us in … oh, dear, this is bad. Oh, no … folks, brace yourselves! The macrophage is about to ———(transmission ended).

Practice problems for these concepts can be found at: Human Physiology Review Questions for AP Biology

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