Table 1.

Biological characteristics of human IgG subclasses.

	IgG1	IgG2	IgG3	IgG4
Natural abundance (%)a	60–70	14–20	4–8	2–6
Half-life (days)a	21–23	20–23	7–8	21–23
Immune Responsea	Induced by protein antigens and membrane proteins	Directed toward polysaccharide antigens	Predominates at the early stage of the viral infection	Dominant response following repeated or long-term exposure to antigen
In vivo Characteristicsb	Stable	Covalent dimers	Prone to protease digestion	Fab arm exchange
Effector functionsc
FcγRI	+++	−	++++	++
FcγRIIA/B,C	+++/+	++/−	++++/++	++/+
FcγRIIIA/B	+++/+++	+/−	++++/++++	++/−
C1q binding	++	+	+++	−

^aAdapted from Ref.¹⁹

^bAdapted from Ref.²⁰

^cAdapted from Ref.²¹