B and T Lymphocytes Utilize Similar Mechanisms To Generate Diversity in Antigen Receptors

The antigenic specificity of each B cell is determined by the membrane-bound antigen-binding receptor (i.e., antibody) expressed by the cell. As a B cell matures in the bone marrow, its specificity is created by random rearrangements of a series

VISUALIZING CONCEPTS

And Lymphocyte Antigen Receptors

FIGURE 1-7

VISUALIZING CONCEPTS

FIGURE 1-7

Overview of the humoral and cell-mediated branches of the immune system. In the humoral response, B cells interact with antigen and then differentiate into antibody-secreting plasma cells. The secreted antibody binds to the antigen and facilitates its clearance from the body. In the cell-mediated re sponse, various subpopulations of T cells recognize antigen presented on self-cells. TH cells respond to antigen by producing cytokines. TC cells respond to antigen by developing into cytotoxic T lymphocytes (CTLs), which mediate killing of altered self-cells (e.g., virus-infected cells).

of gene segments that encode the antibody molecule (see Chapter 5). As a result of this process, each mature B cell possesses a single functional gene encoding the antibody heavy chain and a single functional gene encoding the antibody light chain; the cell therefore synthesizes and displays antibody with one specificity on its membrane. All antibody molecules on a given B lymphocyte have identical specificity, giving each B lymphocyte, and the clone of daughter cells to which it gives rise, a distinct specificity for a single epitope on an antigen. The mature B lymphocyte is therefore said to be antigenically committed.

The random gene rearrangements during B-cell maturation in the bone marrow generate an enormous number of different antigenic specificities. The resulting B-cell population, which consists of individual B cells each expressing a unique antibody, is estimated to exhibit collectively more than 1010 different antigenic specificities. The enormous diversity in the mature B-cell population is later reduced by a selection process in the bone marrow that eliminates any B cells with membrane-bound antibody that recognizes self-components. The selection process helps to ensure that self-reactive antibodies (auto-antibodies) are not produced.

The attributes of specificity and diversity also characterize the antigen-binding T-cell receptor (TCR) on T cells. As in B-cell maturation, the process of T-cell maturation includes random rearrangements of a series of gene segments that encode the cell's antigen-binding receptor (see Chapter 9). Each T lymphocyte cell expresses about 105 receptors, and all of the receptors on the cell and its clonal progeny have identical specificity for antigen. The random rearrangement of the

TCR genes is capable of generating on the order of 109 unique antigenic specificities. This enormous potential diversity is later diminished through a selection process in the thymus that eliminates any T cell with self-reactive receptors and ensures that only T cells with receptors capable of recognizing antigen associated with MHC molecules will be able to mature (see Chapter 10).

How To Bolster Your Immune System

How To Bolster Your Immune System

All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.

Get My Free Audio Book


Responses

  • paolo
    How is the enormously diverse number of b and t cell antigen receptors generated?
    7 years ago
  • Angela
    How are B and T lymphocytes alike?
    7 years ago
  • Demi
    Is the lymphocyte antigen receptor specificity a random process?
    6 years ago
  • david
    What is the similarity & difference between B cell & T cell receptor diversity?
    1 year ago

Post a comment