Antigen recognition in the immune system

Published on October 29, 2020   28 min

Other Talks in the Series: The Immune System - Key Concepts and Questions

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My name is Herman Waldmann from the Dunn School of Pathology in Oxford. I'm going to talk to you about antigen recognition in the immune system. If you recall, I gave you in the first lecture a summary of the overall need of the immune system and how it behaves. In this lecture, I want to discuss how it recognizes the foreign antigen to which it's going to respond in each individual.
Antigen recognition is mediated, as you can imagine, by specific receptors that recognize the antigen. It's very important for detection and elimination of organisms that can cause disease that we call pathogens. Recognition of a foreign antigen is critical for the immune system. It is mediated by very specific antigen receptors that have evolved to do the job. These receptors bind to antigen, signal the immune system to make a response, and also can participate in elimination of the antigen and the pathogens from which it was derived. These receptors can be secreted in the case of antibodies, or can be cell associated in the case of B-cells and T-cells when they are appear on the membrane. An antigen is any structure which can elicit an immune response by being recognized through these cell receptors.
So there are two types of receptors for antigen in the immune system. There are signaling receptors that the B-cells and T-cells carry on their surface. These are made up of a limited number of genes that in the case of B-cell, diversify enormously to make many millions of tension receptors through a wide variety of processes called somatic diversification. There is a similar process for T-cell receptors, but not as vast as you'll see later. Each B-cell ends up with a unique receptor on its surface, and each T-cell ends up with a unique receptor for antigen on its surface. In the case of antigen display receptors, they are not receptors that are there to signal the cell that carries them, but they're to display antigen to T-lymphocytes which recognize the antigen which are being displayed to them. These molecules have limited diversity, and all of it is inherited as part of what is called polymorphism in the species. We vary in various of the MHC class 1 and class 2 genes that we carry. As a result, we display different types of antigens to our T-lymphocytes.