Skip to main content

Session 4: Immune defences against infectious diseases

Completion requirements
View all sections of the document

This is a schematic diagram showing part of a leukocyte cell membrane with a receptor molecule in its surface. A small region of the outward-facing part of the receptor is identified as the binding site. Close to the leukocyte cell membrane is a pathogen surface in which there is an antigen molecule. A small part of the antigen, the active site, has a shape that fits into the binding site of the receptor. Part (b) shows the receptor bound to the antigen, and this binding initiates a chain reaction that alters the leukocyte’s activity.