recap

41.5 recap

The cellular immune response acts against virus-infected or mutated body cells. Specific receptors on T cells bind to antigen–MHC complexes displayed on cell surfaces. During development, T cells are selected that recognize MHC proteins. T-helper cells bind antigens on MHC II proteins and contribute to the humoral immune response. Cytotoxic T cells bind antigens on MHC I proteins and contribute to the cellular immune response. Tregs suppress immune responses to self antigens.

learning outcomes

You should be able to:

  • Summarize the role of MHC proteins in the humoral immune response.

  • Provide reasonable speculation regarding how drugs could generate immunosupression by targeting T-helper cells, and predict the side effects of these drugs.

  • Describe how Tregs suppress the cellular and humoral immune systems.

  • Predict consequences of inappropriate levels of activity of Tregs.

Question 1

MHC proteins almost always differ among unrelated people, so organ transplants usually provoke a cellular immune response by the host, causing rejection. People receiving transplants are given a drug called cyclosporine which inhibits T cell development. How do you think cyclosporine works?

By inhibiting T cell development, cyclosporine blocks TH cell binding to transplanted cells. This stops cellular immunity from occurring, because TH cell binding releases cytokines to attract TC cells that would kill the transplanted cells.

Question 2

When a virus infects a cell, the immune system mounts an adaptive response to this infection. What are the roles of the T cell receptor and MHC protein in this response?

Inside the infected cell, the virus is broken down into fragments, and some peptide fragments are displayed on the cell surface along with MHC protein (class I). A cytotoxic T cell displaying a T cell receptor that is specific for the peptide on the target cell binds to the target cell and initiates the cellular immune response.

Question 3

Cancer cells often express proteins that the body has never seen, so they are targeted by the cellular adaptive immune system. In some cancers, however, Tregs are increased in numbers and activity. Why would this indicate a poor prognosis?

Increased Treg activity would inhibit the cellular immune response, so the tumor would evade the adaptive immune system.

Given the numerous and complex cellular interactions that activate the immune system and generate antibody diversity, you may have perceived many points at which the immune system could fail. We will now turn to several situations in which one or more components of this complex system malfunction.