Final answer:
Yes, an IgG typically has a higher affinity than the original IgM due to the process of affinity maturation that takes place after repeated exposure to an antigen. IgM has its strength in its avidity due to multiple binding sites, which compensates for its lower affinity per site. IgG is particularly important for late primary responses and secondary immune responses, providing robust and sustained protection.
Step-by-step explanation:
When considering whether an IgG has a higher affinity than the original IgM that gave rise to it, the answer is typically yes. Affinity refers to the strength of a single antibody-antigen interaction, and IgG antigen binding sites generally have a higher affinity for their target. This is largely due to a process known as affinity maturation, which occurs during the primary immune response where B cells undergo somatic hypermutation resulting in variations in the antigen-binding sites of antibodies. Those B cells that produce antibodies with a better fit for the antigen proliferate, leading to the selection of B cells producing IgG with higher affinities.
Conversely, IgM, which is usually the first antibody class to be produced in response to an antigen, typically has lower affinity antigen-binding sites. However, because IgM is secreted as a pentamer, it has ten antigen-binding sites, leading to high avidity which compensates for the lower affinity. This enables IgM to be very effective in binding a wide array of pathogens initially.
The role of IgG becomes more prominent in late primary responses and is the main antibody in secondary responses. This antibody class not only clears pathogens from the blood, but also has the ability to activate complement proteins. Importantly, IgG can cross the placenta, providing protection to the developing fetus. After repeated exposures to an antigen, the immune system's memory cells are activated and produce IgG antibodies with increased affinity for the antigen, providing a stronger and more sustainable immune response.