Question

1. Identify the antigen receptor molecules and component proteins for B and T cells 2. Identify the function of an antigen receptor. 3. Describe the interaction between receptor and antigen.

Answer 1

Step 1

Antigen is a foreign particle which induces an immune response in the body by the production of antibodies.

Receptor is a protein molecule present on the cell surface which receives chemical signal from outside the cell and causes a cellular response.

Step 2

Antigen receptors on B cells called B-cell receptor or BCR and T cells called T-cell receptor or TCR are protein complexes made up of variable antigen-binding chains, the heavy and light immunoglobulin chains in the B-cell receptor and the TCRα and TCRβ chains in the T-cell receptor that are associated with invariant accessory proteins. The invariant chains are required both for transport of the receptors to the cell surface and, most importantly, for initiating signaling when the receptors bind to an extracellular ligand. Antigen binding to the receptor generates signals that lead ultimately to the activation of nuclear transcription factors that turn on new gene expression and turn off genes typically expressed only in resting cells. In this part of the chapter we also see how clustering of the antigen receptors with co-receptors helps to generate these signals.

2. B cells and T cells have surface receptors for antigen. Each cell has thousands of receptors of a single specificity, that is with a binding site for a particular epitope.

T-cell receptors (TCRs) enable the cell to bind to and, if additional signals are present, to be activated by and respond to an epitope presented by another cell called the antigen-presenting cell.

B-cell receptors (BCRs) enable the cell to bind to and, if additional signals are present, to be activated by and respond to an epitope on molecules of a soluble antigen. The response ends with descendants of the B cell secreting vast numbers of a soluble form of its receptors. These are antibodies, which are glycoproteins.