Question

A. Describe how T cell receptors differ from immunoglobulins. Include information on their generation, structure, and function.

B. Explain the primary difference in how B cells recognize antigens verses T cells

C. Explain the effect of immunoglobulins not being able to undergo isotype switching.

D. Explain the effect if cells lost their MHC II molecules.

Answer 1

A] T-cell receptors [TCR] are molecules found on the surface of T-cells or T-lymphocytes. It is responsible for recognising fragments of antigens bound to MHC molecules [ major histocompatibility complex]. They cannot bind to an antigen without this complex formation.

TCRs are known to be clone specific, heterodimeric polypeptide chains. In humans, most T-cells express a TCR composed of alpha and beta cells and a few T-cells express TCRs with gamma and delta chains.

The TCR through its CDRs enables the T-cells to recognize and respond to foreign or 'non-self' materials. APCs

or Antigen presenting cells digest pathogens and the fragments are displayed on the major histocompatibility complex molecules. This MHC-antigen complex binds to the TCR while other co-stimulatory molecules are activated leading to the activation, proliferation, differentiation, apoptosis or cytokine release.

Immunoglobulins or antibodies are produced by the white blood cells in response to an antigen. They are glycoprotein molecules and act as a critical part of the immune response by binding to a specific antigen such as a bacteria or virus and then destroying it. There are 5 types of immunoglobulins -- IgA, IgD, IgE, IgG and IgM.

Immunoglobulins are made up of two heavy chains and two light chains and have a Y shaped structure. Functionally, they can be separated into a variable [V] domain that binds to the antigen and a constant [C] domain that specifies effector functions such as activation of compliment or binding to Fc receptors.

B] The primary difference between the action of T-cells and B-cells is that B-cells can bind to soluble antigens. B-cells produce antibodies upon activation that can destroy invading bacteria, viruses and toxins. Thus their function is in the humoral response to antigens.

In short, we can say that while B-cells can directly connect to antigens on the surface of the invading bacteria or virus, the T-cells can only connect to parts of virus antigens on the outside of infected cells.

T-cells destroy the body's own cell if it has been taken over by viruses or has become cancerous.