Content Reviewers:Rishi Desai, MD, MPH
The immune response is highly specific for each invader, and that’s because the cells of the adaptive immune response have unique receptors that are able to differentiate friendly bacteria from potentially deadly pathogens from their unique parts - called antigens.
The remainder of the heavy chain makes up the constant region or constant fragment region, also called Fc.
The two heavy chains are linked to one another by disulfide bonds and each heavy chain is also linked to a light chain by a disulfide bond.
Each B cell receptor, has two identical heavy and light chains, resulting in two identical antigen binding sites.
However, the heavy chain actually changes as the B cell develops.
These five are encoded by heavy chain genes which are referred to by the greek letters mu, delta, gamma, alpha, and epsilon.
Each of these immunoglobulins has a different function, shape, and consequently valence.
The valence of an antibody is the amount antigen binding or Fab fragments it has.
It makes up approximately 4% of the immunoglobulin found in the serum.
This is because it serves as the the B cell receptor, and like a transformer, it has two completely different conformations.
When it’s serving as the B cell receptor it’s a monomer, and it has a valence of 2 meaning that it has two Fab regions.
Because it’s a pentamer, secreted IgM has a valence of 10.
IgG is the most abundant immunoglobulin, making up 75% of the immunoglobulin found in serum!
The IgG molecule is a monomer made up of two gamma heavy chains and two light chains, so its valence is 2.
Normally, bacteria have an antiphagocytic capsule which makes them slippery and hard to grab.
Opsonization is the process by which pathogens are coated with molecules so that they can be more easily picked up and eaten by phagocytes.
Imagine trying to pick up a slippery meatball with your fingers versus stabbing it with a fork and then just having to pick up the fork. Opsonization also makes it easier to eat meatballs faster too.
IgG is also great at activating the classical complement pathway, which helps destroy extracellular pathogens like bacteria.