How can IgA survive ??

[Jemmy]

someone asked me this question & I need an explanation ,,,,
when baby acquire a passive immunity (IgA) from his mother in milk by breast feeding , why IgA in milk doesn't undergo degradation & destruction in the stomach of the baby .
so if anyone knows any explanation please, post it .
thanks

[lilybucket]

If I remember rightly, it has a dimer which secretes a substance which protects against gastric juices

[zhangyuzhi]

someone asked me this question & I need an explanation ,,,,
when baby acquire a passive immunity (IgA) from his mother in milk by breast feeding , why IgA in milk doesn't undergo degradation & destruction in the stomach of the baby .
so if anyone knows any explanation please, post it .
thanks

hi there. I am not a medic but a biochemist. I will try to explain this way:

1. Secretory IgA (sIgA) is indeed degraded but rather slowly. It has a half-life of several days.

2. The molecule resists proteolysis by the fact that the hinge region of the monomers as well as the J-chain (joining the monomers) are heavily glycosylated. This creates a steric barrier for proteases and proteinases to act upon the molecule, which essentially leads to cleavage.

In particular, glycosylation at hinge region is typically O-linked, which means the glycan structures are relatively simpler and smaller. This also confers flexibility to the antibody (you know, orientation w.r.t the antigen blah blah).

hope this helps.

[zhangyuzhi]

If I remember rightly, it has a dimer which secretes a substance which protects against gastric juices

I don't think sIgA dimer can secrete anything by itself, but rather it is the product of mucosal secretion. Do you actually mean the secretory component? It's indeed implicated in immunity though...but it is still a part of polymeric IgA receptor prior to cleavage.

[Jemmy]

hi there. I am not a medic but a biochemist. I will try to explain this way:

1. Secretory IgA (sIgA) is indeed degraded but rather slowly. It has a half-life of several days.

2. The molecule resists proteolysis by the fact that the hinge region of the monomers as well as the J-chain (joining the monomers) are heavily glycosylated. This creates a steric barrier for proteases and proteinases to act upon the molecule, which essentially leads to cleavage.

In particular, glycosylation at hinge region is typically O-linked, which means the glycan structures are relatively simpler and smaller. This also confers flexibility to the antibody (you know, orientation w.r.t the antigen blah blah).

hope this helps.

Thanks a lot,
this is really helpful ,,, so the trick is in the hing region & the J chain !!
I got it ....thank u