0:00 Now, let's talk about IgA antibodies. 0:08 IgA antibodies are important in the mucosal system. 0:12 Here again, we have the mucosal surfaces, epithelial cells, and here of the 0:16 blood vessel 0:16 underneath it. 0:17 Now, this is the laminopropia of any mucosal system. 0:23 It can be in the nasal, the gut, or the bronchus, for example. 0:28 I mentioned before that the plasma cells become activated once they leave the 0:33 blood vessel 0:34 into the tissue and with the help of T helper cells. 0:37 So here we have an IgA B lymphoblast, leaving the blood vessel and becomes the 0:42 IgA producing 0:44 plasma cell. 0:46 When the plasma cell produces IgA, it produces it in a dimeric form within the 0:52 mucosal system. 0:54 The dimeric form is when the two IgA monomers are connected to each other by a 0:59 J chain. 1:00 However, if the IgA is secreted in the bloodstream, the IgA is usually monomer 1:05 ic, just one of 1:06 them secreted, like so. 1:11 Another important thing is that plasma cells are not usually found in inductive 1:15 sites, 1:15 such as in the gut, the inductive site being the payer's patches. 1:19 So plasma cells are not really found in payer's patches. 1:22 Those plasma cells are effector cells, so they are usually found in the laminop 1:26 ropia, 1:27 where they can secrete antibodies to protect against infection. 1:33 Now that the plasma cell has secreted antibodies, these IgA antibodies, what 1:38 happens next? 1:39 Well, the IgA, the dimeric IgA antibody, can move from the laminopropia into 1:44 the lumen, 1:45 where it can help prevent antigens from entering our body, entering the mucosal 1:52 surface, for 1:53 example. 1:54 There are special receptors on the basal aspect of these epithelial cells, 1:59 called PIGR, which 2:01 actually has affinity for the dimeric IgA antibodies. 2:07 And once the IgA antibody binds to the PIGR, it gets endostatized within the 2:13 cell and 2:13 then expelled out into the lumen. 2:17 And now, as it does this, the dimeric IgA antibody, the J chain, takes part of 2:22 the PIGR 2:24 receptor, and forms the IgA plus the secretory component. 2:31 So now we have many IgA antibodies within the lumen. 2:34 So what do they do now? 2:36 How do they prevent antibodies from invading or causing an infection within the 2:42 mucosal 2:42 cells? 2:43 Well, for example, it can do three things. 2:48 If we have antigen pathogens within the lumen, the secreted IgA form can bind 2:55 on these pathogens 2:56 and antigens and neutralize them, so prevent them from invading or infiltrating 3:03 a cell. 3:04 Another thing antibodies can do, if the dimeric antibodies, if it's secreted 3:08 within the laminopropia, 3:09 and antigens are present already in the laminopropia. 3:13 The dimeric IgA antibody can bind to these antigens present here, and then 3:19 following 3:20 this, bind on the PIGR receptor on the basal aspect of the cell, and then with 3:26 the antigen 3:27 be transported out into the lumen, taking up part of the PIGR receptor. 3:35 So now we have the IgA plus the antigen and the secretory component. 3:41 So what happened here? 3:42 So IgA can export pathogens and antigens out of the laminopropia into the lumen 3:48 . 3:48 And the final thing, or one of the other main things IgA antibodies can do, is 3:56 that if an 3:57 antigen has infiltrated a cell, the IgA antibody can bind to the PIGR receptor 4:04 of the cell 4:05 that has been infiltrated, and essentially bind with the antigen within the 4:10 cell and 4:10 then transport it out. 4:13 So number three, the IgA can bind and neutralize an antigen within the cell. 4:22 So that concludes these videos on the mucosal immune system. 4:26 The mucosal immune system once again is very important in preventing pathogens 4:33 from invading 4:34 our body and from preventing infections. 4:36 Another important thing is that if an immune response is generated within one 4:40 area of the 4:41 mucosal system, it can generate the immune response in other areas, such as if 4:47 an immune 4:48 response is generated within the nasal cavity, the nasal mucosal tract, it can 4:53 generate the 4:53 same immune response in the vaginal tract or the gut. 4:56 So therefore, it can create both a mucosal immune response and also a systemic 5:01 immune 5:01 which is very important, for example, in the development of vaccines.
