Interactive animations: the molecular interactions between antigen and antibody, and a virtual laboratory of India-ink injections and dissections to study the lymphoid organs of the mouse.
“We live in a potentially hostile world filled with a bewildering array of infectious agents of diverse shape, size, composition and subversive character which would very happily use us as rich sanctuaries for propagating their ‘selfish genes’ had we not also developed a series of defense mechanisms at least their equal in effectiveness and ingenuity. It is these defense mechanisms which can establish a state of immunity against infection (Latin immunitas, freedom from) and whose operation provides the basis for the delightful subject called ‘immunology’.” Ivan M. Roitt, 2013. Essential Immunology.
Explore the hydrogen, hydrophobic, electrostatic and van der Waals bonds that hold antigen and antibody together.
Antigen is any substance able to bind specifically to an antibody or T-cell receptor. However, not every antigen is able to stimulate an immune response. When it does, we call it an immunogen.
Immunogen is a molecule capable of inducing a specific immune response. Therefore, every immunogen is an antigen, but not every antigen is an immunogen — as is the case with haptens, small molecules that become immunogenic when conjugated to a specific carrier.
Epitope is a small part of the antigen's molecular structure that is recognised by an antibody.
Antibodies are glycoprotein molecules produced by plasma cells in response to an immunogen. They bind specifically to a part of the antigen known as the antigenic determinant or epitope.
All immunoglobulins have a four-chain structure as their basic unit: two identical light chains (around 23 kDa) and two identical heavy chains (50–70 kDa) held together by disulfide bonds. Three-dimensional images show that the molecule is not straight as represented in the animation: the hinge region is its flexibility site. It also presents an invariant fragment (Fc) and Fab fragments, which contain the antigen-binding site.
Based on differences in the amino-acid sequences of the heavy-chain constant region, immunoglobulins are divided into five classes:
“Antigen–antibody interactions” by Luiz Anastácio Alves, Thais Faggioni, Filipe Faria Berçot and Rodrigo Bisaggio is licensed under Creative Commons BY-NC-SA 4.0.
Drag-and-drop simulations of India-ink injections and dissections in the mouse.
Everything in a single player, without switching tabs: choose the route and follow the virtual practice and the dissection — intradermal (footpad injection → popliteal lymph node) or intravenous (tail-vein injection → lymphoid organs).