Table 1.

Structural, biological, and functional properties of IgG subclasses

Characteristics	IgG1	IgG2	IgG3	IgG4
Structural
Molecular weight (kDa)	150	150	155–165	150
Disulfide bond between heavy chains	2	4	11	2
H chain type	γ1	γ2	γ3	γ4
Ig H constant gene	IGHG1	IGHG2	IGHG3	IGHG4
Glycosylation site	297	297	297	297
N-linked glycans per H chain	1	1	2 *	1
O-linked glycans per H chain	0	0	3	0
Biological
Biological half-life (days)	21–24	21–24	7–8	21–24
Mean adult serum level (g/L)	6.98	3.8	0.51	0.56
Placental transfer	+++	++	++/+++*	++
Functional (binding—activation)
C1q- CDC	++	+	+++	–
FcγRI (CD64) on monocytes—ADCP	+++	–	+++	++
FcγRIIa (CD32a)-H131 on monocytes and neutrophils—ADCP (ADCT⇞)¨	++	++	++	+
FcγRIIa (CD32a)-R131 on monocytes and neutrophils—ADCP (ADCT⇞)¨	++	–	++	+
FcγRIIb (CD32b) on monocytes and neutrophils—ADCP	+	–	++	+
FcγRIIIa (CD16a)-F158 on NK cells—ADCC	++	–	+++	–
FcγRIIIa (CD16a)-V158 on NK cells—ADCC	+++	+	+++	+
FcγRIIIb (CD16b)NA1 on neutrophils and monocytes—ADCP (ADCT⇞)¨	+++	–	+++	–
FcγRIIIb (CD16b)NA2 on neutrophils and monocytes—ADCP (ADCT⇞)¨	+++	–	+++	–
FcRn on epithelial, endothelial, macrophages/monocytes and dendritic cells—homeostasis—pH 7,4 / < 6,5	+/+++	+/+++	+/+++	+/+++

Number of ( +) symbols indicates the affinity/interaction magnitude of each one of the immunoglobulin subclasses. *IgG allotype-specific. ⇞Mechanism demonstrated for IgG1-TmAb. CDC: Complement-dependent cytotoxicity. ADCP: Antibody-dependent cellular phagocytosis. ADCC: Antibody-dependent cellular cytotoxicity. ADCT: Antibody-dependent cellular trogocytosis. FcRn: Neonatal Fc receptor. N-linked glycans connect the sugar to an asparagine residue in the glycosylation process, whereas O-linked glycans connect a serine or threonine residue