Properties of IgG subclasses

Subclass	IgG1	IgG2	IgG3	IgG4
% of total IgG	60 to 70	20 to 30	5 to 8	1 to 4
Heavy chain	gamma1	gamma2	gamma3	gamma4
Heavy chain constant components (CH)	CH1, CH2, CH3	CH1, CH2, CH3	CH1, CH2, CH3	CH1, CH2, CH3
MW	150 kD	150 kD	150 kD	150 kD
Half-life (days)	21 to 24	21 to 24	7 to 8	21 to 24
Ability to activate classical complement pathway	++	+	+++	–
Important in antibody response to:
Proteins	++	±	++	++
Polysaccharides	–	+++	±	±
Allergens	–	–	–	++
Fc-gamma-receptor binding	I, II, III	II	I, II, III	I, II
Placental transport	++	+	++	++

IgG: immunoglobulin G; CH: constant heavy chain; MW: molecular weight.

Adapted from:

Schroeder HW Jr, Cavacini L. Structure and function of immunoglobulins. J Allergy Clin Immunol 2010; 125:S41.
Carsetti R, Plebani A, Ugazio AG, et al. B lymphocytes and immunoglobulins. In: Immunology IV: Clinical Application in Health and Disease, Bellanti JA (Ed), Care Press, Bethesda, MD 2012. p.163.
van der Berg M, Weemaes CMR, Cunningham-Rundles C. Isotype defects. In: Immune Deficiencies, Sullivan KE, Stiehm ER (Eds), Academic Press Elsevier, Amsterdam 2014. p.389.

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