What immunoglobulins are most sensitively detected using complement-mediated cytotoxicity assays?

Complement-mediated cytotoxicity assays are designed to evaluate the effectiveness of antibodies in lysing target cells, typically through a process that activates the complement system. Among the various immunoglobulins, IgG3 and IgM are particularly effective in this context.

IgM is the first antibody produced in response to an infection and has a pentameric structure that allows it to strongly activate the complement system, leading to efficient opsonization and subsequent cell lysis. Its size and structure provide multiple binding sites for complement components, enhancing its ability to initiate the complement cascade.

IgG3 is known to have the highest complement activation potential among the IgG subclasses. Its ability to form strong interactions with complement proteins, particularly C1q, makes it highly effective in promoting complement-mediated cell lysis. The other subclasses of IgG have varying abilities to activate complement, but IgG3 stands out due to its superior activation capacity.

In summary, the combination of IgG3 and IgM in complement-mediated cytotoxicity assays results in the most sensitive detection of immune responses due to their robust complement activation properties, making them the most relevant immunoglobulins in this context.