The function of immunoglobulin A in immunity

Abstract

The vast surfaces of the gastrointestinal, respiratory, and genitourinary tracts represent major sites of potential attack by invading micro-organisms. Immunoglobulin A (IgA), as the principal antibody class in the secretions that bathe these mucosal surfaces, acts as an important first line of defence. IgA, also an important serum immunoglobulin, mediates a variety of protective functions through interaction with specific receptors and immune mediators. The importance of such protection is underlined by the fact that certain pathogens have evolved mechanisms to compromise IgA-mediated defence, providing an opportunity for more effective invasion. IgA function may also be perturbed in certain disease states, some of which are characterized by deposition of IgA in specific tissues. This review details current understanding of the roles played by IgA in both health and disease.

Teleost skin, an ancient mucosal surface that elicits gut-like immune responses

“…In addition, immune responses in the aforementioned mammalian mucosal surfaces present also commonalities with those observed here in the fish skin. Thus, it has also been shown that microbial infections in these mammalian mucosal surfaces generally induce a local mucosal response governed by a mucosal Ig (sIgA) and that, in some cases, the systemic response is dominated by IgG/IgM (31,32). Moreover, similar to the accumulations of IgT + B cells shown here in the skin epidermis of infected fish, significant accumulations of B cells have also been described upon infection in the MALT of nose (33), gut (16,34), lung (35), and uterus (36).…”

Dysfunctions of the Iga system: a common link between intestinal and renal diseases

“…With the exception of the upper domains of the Fc region (the C H 1 domains), the domains are arranged in pairs, stabilized by numerous non-covalent trans interactions. 7 In humans, IgAs are divided into closely related subclasses, IgA1 and IgA2, which differ by the absence of a 13-amino acid sequence in the hinge region of the IgA2 molecule. 1 The lack of this region in IgA2 allows it to be resistant to the action of bacterial proteases (i.e., those from Streptococcus mutants, Neisseria meningitidis and Haemophilus influenzae) that cleave IgA1 in the hinge region and may underlie the predominance of IgA2 in mucosal secretions.…”

“…1 The lack of this region in IgA2 allows it to be resistant to the action of bacterial proteases (i.e., those from Streptococcus mutants, Neisseria meningitidis and Haemophilus influenzae) that cleave IgA1 in the hinge region and may underlie the predominance of IgA2 in mucosal secretions. 7 IgA SYNTHESIS The forms of IgA in serum and mucosal secretions, the two main compartments in which these antibodies are found, differ. In serum, IgA exists mainly in its monomeric form (about 85-90%).…”

“…1 Moreover, in humans intestinal SIgA originates only from the gut-associated lymphoid tissue, but is generated from two sources in mice: B2 lymphocytes in organized germinal centers of mucosal lymphoid tissues such as Peyer's patches (T lymphocyte-dependent IgA production) and B1 lymphocytes developed in the peritoneal cavity and distributed in the intestinal lamina propria (T lymphocyte-independent IgA production). 7 IgA GLYCOSYLATION IgA is the most glycosylated form of Ig. Both subclasses carry a number of N-linked carbohydrates, contributing 6-7% of molecular mass of IgA1 and 8-10% of IgA2.…”

Translocalized IgA mediates neutralization and stimulates innate immunity inside infected cells

“…M ore IgA is produced per day in the human body than all of the other antibody isotypes combined (1). Humans express two IgA isotypes, IgA1 and IgA2, and each isotype is expressed in several oligomeric states including, monomeric (mIgA), dimeric (dIgA), and secretory (S-IgA) (1).…”