Table 1.

Differences in the IgA form and subclass distribution in the serum and secretions in healthy human.

	SERUM IgA	MUCOSAL IgA
Production location	Plasmablast and plasma cells in the bone marrow, spleen, lymph nodes, tonsils [12]	Plasmablast and plasma cells located in the lamina propria of mucosal system (MALT, PP, ILF etc.) [20]
Production	≈ 1.2 g per day (adult human)	≈ 3.2 g per day
Form	75–90% monomeric, [12] 10–15% in polymeric form, [12] 1% bound in circulating immune complexes	Mucosa: 95% SIgA [12] lamina propria: predominantly pIgA, scarce mIgA
Subclass	85% IgA1, 12% IgA2 [12] 101 ± 26 (IgA1) and 14 ± 4 (IgA2) mg/kg body weight	% of IgA1 and IgA2 varies and depends on the mucosal area, i.e., tears, saliva, respiratory mucosa, vaginal, genital intestine (see Figure 1)
Function	Anti-inflammatory effects: binding of mIgA to FcαRI induce inhibitory effects and downregulates IgG-mediated phagocytosis, chemotaxis, bactericidal activity, oxidative burst activity, and cytokine release [21].	Bacteriostatic activity Barrier for microbiota (pathogens, and commensal bacteria), toxins from crossing the epithelial layer; neutralization of intracellular pathogens [13,18]
Clearance	Catabolized in liver, kidney, skin; a half-life ~5 days. Phagocytosis of IgA-Ag complex [22]	Secreted into lumen (excreted) Phagocytosis of IgA-Ag complex when in lamina propria or intraepithelial

Legend: MALT: mucosa associated lymphoid tissue; PP: payers patches; ILF: isolated lymphoid follicles. In the literature, differences in the amounts and percentages of mIgA/pIgA can be found, however, the amounts and percentages are stated mostly to get brief insight into the field.