Welcome y'all to Pixerize a Scene on Immunoglobulin A, or IgA for short. IgA is one of the most important immunoglobulins, or antibodies, in the human body because it provides immunity at mucosal membranes, specifically in secretions like tears, saliva, and mucus. In this video, I'll give you my visual mnemonic to help you remember everything you need to know about IgA.
Let's start by reviewing what an immunoglobulin even is. Immunoglobulins are Y-shaped antibodies made by B cells. They contain a variable region, also called fragment antigen binding, or FAB, since this area is responsible for recognizing and binding to foreign antigens.
On the other side, antibodies have a constant region, also called fragment crystallizable, or FC, that basically talks to other pieces of the immune system. It's also this constant FC part that determines the class of an antibody. There are five major classes of immunoglobulins that you need to know for test day, namely IgA, IgE, IgD, IgM, and IgG. It can be hard to keep the different classes straight, so let's dive right into this mnemonic to learn all about IgA.
Welcome to the Pixerize farm. Check out how one of our dairy cows here is munching on hay. Notice specifically how the cow is munching right through the middle of this hay bale, making this hay look kind of like the letter Y.
And you know what else looks like the letter Y? That's right, antibodies. Since hay is our recurring symbol for the letter A, this Y-shaped hay, or antibody-shaped hay, is our memory anchor for immunoglobulin A, or IgA.
Now that we've oriented you to IgA, let's learn what makes IgA different than all the other antibodies. Our farmer is milking the cow, and he's come prepared with his buckets. Or rather, he has two buckets, or pails, connected to a stick. You know how farmers balance these milkman's yokes over their shoulders, holding up buckets on each side? It's a real thing, I promise.
By the way, the two buckets connected to each other should help you remember that IGA usually is found as a dimer. The di refers to the number two, and mer just means part. So a dimer just means that two parts of IgA are found together.
Generally, two molecules of IgA are connected via a J-chain, or joining chain, to form a dimer. To note, IgA may be found circulating in the blood in low amounts by itself, or as a monomer. However, the majority of IgA in our bodies is secreted in a dimeric form.
You should really just think of IgA as a dimer, and you'll be set for test day. And what was our farmer up to? Oh, that's right, milking the cow.
Won't we just appreciate the fresh milk getting secreted by the cow here? By the way, this secretion of milk should help you remember that IgA is primarily found in body secretions, like tears, saliva, mucus, and breast milk. Since these secretion sites can be a site of foreign invasion, IgA works to protect us against infection at these sites. A particularly high yield point, also represented by the milk here, is that IgA is found in early breast milk, which is formally called colostrum.
This secreted IgA provided by the mother in this milk ends up coating the baby's intestines, providing the baby protection from infection. The secreted nature of IgA in milk is part of the reason why mothers are recommended to breastfeed their babies for the first six months of life. It gives these babies an extra immunity boost. Alright, let's shift our gaze to the water trough. No farm would be complete without a water trough, right?
And since these water troughs are exposed to the elements, they always have this slimy, mucusy stuff growing in them, like algae. Yep, this green, slimy algae sure reminds me a lot of mucus. Coincidentally, this mucus-like appearance can help you remember that IgA is found in mucus membranes and therefore provides mucosal immunity. This should make sense since we just said that IgA is secreted into body fluids like mucus, saliva, tears, and breast milk.
All of these body fluids come from, you guessed it, mucus membranes. Since bacteria and viruses can attach to these mucosal surfaces to invade our bodies, putting antibodies in mucosal secretions can help protect us from infections at these sites. Secreted IgA binds and neutralizes these foreign bugs.
preventing their attachment. Mucus membranes are found all over our bodies, and I like to think of them as any naturally wet surface, like our mouth, GI tract, or airways. IGA, importantly, can be found at all of these sites, working to protect us from foreign invasion.
Thanks, IGA. You're the best. Alright, now let's pivot to the farmer. See how his clothes have these characteristic patches?
I feel like all farmers wear patches. Anyway, these patches should remind you of Pyre's patches, one of the major sources of IGA. The IGA produced by Pyre's patches lines the epithelium of the GI tracts.
This is important because many foreign bugs can enter our GI tracts through the food we eat. IgA in our GI mucosa serves a critical role in protecting us from these pathogens, especially from parasites like Giardia. In fact, patients born with congenital defects in IgA end up getting recurrent Giardia infections.
But you can check out our dedicated video on selective IgA deficiency to learn more about that. Yippity-doo-dah! It's been a great day on the farm.
Let's recap and get back to the city, yeah? Immunoglobulin A, or IgA, is a major class of antibodies found in secretions like tears, saliva, mucus, and notably, colostrum or breast milk. It is secreted in a dimeric form, that is, as two antibodies connected by a joining chain.
IgA provides immunity at mucosal membranes, like the GI and respiratory tracts. and is importantly made by Peyer's patches in the intestines. That's all we've got for IGA folks, I'll see you at the next harvest.