0:00 Armando Housurgam biology and medicine videos, please make sure to subscribe, 0:03 join the farming 0:04 group for the latest videos, please visit Facebook, Armando Housurgam, please 0:06 like, and 0:06 here you can also ask questions, answer questions, and post some interesting 0:09 things, including 0:10 Alex, or send them to me. 0:12 And you can also change the quality settings to the highest one for better 0:16 graphics. 0:16 Now in the previous video, we looked at the activation of the naive T cells, 0:20 such as the 0:21 naive CD8 cell becoming a T killer cell and the naive CD4 cell becoming 0:24 different types 0:25 of T helper cells. 0:27 CD helper cells has another important role in that it also activates B cells 0:31 within the 0:32 germanol center, the B cells which have already recognized the antigen. 0:37 So in this video, we're going to concentrate on B cell activation and 0:41 differentiation. 0:42 So in the lymph node, the germanol center, the B cells are mature and prolifer 0:47 ate and 0:48 also differentiate. 0:49 So if we have the B cell here, if it is activated and it's finally 0:54 differentiated, it will become 0:56 either a plasma cell or a memory B cell typically. 0:59 The plasma cells is the secreting antibody cell. 1:03 So going back to this diagram, we have the B cell becoming memory cells and the 1:07 plasma 1:08 cells here. 1:09 Now the T killer and all the other types of T cells, including the T helper and 1:13 also the 1:13 plasma cells will travel out of the lymph node via the efferent lymphatic 1:18 vessel from the 1:19 lymph node. 1:20 Then these T cells and plasma cells will travel through the lymphatic 1:25 circulation and the T 1:27 cells will then migrate to the tissue where the site of infection, infiltration 1:31 , inflammation 1:32 is. 1:33 Plasma cells can also migrate to the tissue where it will begin secreting 1:37 antibodies to 1:38 help enhance or promote the innate immune response. 1:44 However, these plasma cells which move into the tissues are typically the short 1:49 -lived plasma 1:49 cells, right? 1:52 The long-lived plasma cells which we are going to concentrate on will move into 1:57 the bone marrow. 1:58 They will migrate into the bone marrow and there they will secrete the 2:02 antibodies, specific 2:03 antibodies into the bloodstream or the lymphatic circulation. 2:08 These antibodies will then travel around the body and typically enter the site 2:12 of inflammation 2:13 and infection and promote the immune response to destroy the pathogen. 2:20 Hope you understood that. 2:21 That was an overall picture. 2:22 Now let's look at the big immunology map again and look at the B cell 2:25 activation in 2:26 more detail. 2:28 Here is where we last left off in the previous video where the T helper cell 2:31 activates the 2:31 B cell in the general center. 2:33 Let's have a closer look at this process by zooming into the general center 2:38 over here. 2:39 So we zoom in. 2:40 So here we have in orange the general center. 2:43 The terminal center is divided into the dark zone and the light zone. 2:50 The immature B cell which has just taken in a pathogen and then expressed the 2:56 antigen 2:57 of the pathogen on the MHC will be in the dark zone and will wait for the T 3:04 helper cell. 3:05 And the T helper cell came from if you remember a naive T cell which became 3:10 activated itself 3:11 through an antigen presenting cell such as a dendritic cell. 3:14 So this naive T cell became a T helper. 3:17 The T helper will then bind with the B cell and secrete cytokines which will 3:22 then activate 3:23 the B cell itself. 3:25 Let's look at this process in a bit more detail. 3:27 So here we have the T helper cell. 3:29 It has a CD4 co-receptor, a TCR, a T cell receptor and also a CD40 ligand 3:39 receptor. 3:41 And then the B cell has an MHC class 2 which presents the antigen to the T 3:45 helper cell and 3:46 also a CD40 receptor. 3:49 The CD40 ligand of the T helper cell is important because it stimulates the B 3:53 cells proliferation 3:54 and differentiation as well as some cytokines which are created by the T helper 3:59 cell such 4:00 as cytokines interleukin 4, interleukin 6 and interleukin 5 or interleukin 4, 5 4:07 , 6. 4:08 So let's go back to this general center here. 4:10 So when this image of B cell became activated to the T helper cell, the image 4:14 of B cell will 4:15 begin to undergo what's called somatic hyper mutation and also proliferate in 4:21 the process. 4:22 So all these are proliferated B image of B cells are called central blasts in 4:27 the dark 4:28 zone and they all have unique antibodies now because of somatic hyper mutation. 4:34 Now let's stop there and go to the light zone. 4:36 In the light zone it's important to know that we have special type of T helper 4:40 cells as well 4:41 known as T helper follicular cells. 4:45 And also we have follicular dendritic cells. 4:48 And they are in the light zone because they will essentially proceed with the 4:53 activation 4:53 and maturation of the B cells, the central blasts you can say now. 4:59 Okay, the central blasts are in the dark zone and they all have their unique 5:04 antibodies. 5:05 So they have to move into the light zone. 5:07 They move into the light zone because they also express some proteins such as C 5:13 XCR4 and 5:13 CXCR5, which are attracted to chemical signals coming from the light zone. 5:22 And so they would move from the dark zone into the light zone because of this 5:26 attraction. 5:27 So just recapping the B cells proliferate and undergo affinity mutation through 5:32 somatic 5:32 hyper mutation. 5:34 I wrote here maturation, that's not right, sorry. 5:38 And they also will begin expressing proteins such as CXCR4 and CXCR5, which are 5:45 attracted 5:45 to the chemokime coming from the light zone, in this case CXCL13. 5:52 So the central blasts will move from the dark zone to the light zone. 5:56 And they will become a central site in the light zone. 6:01 central blasts can either have high affinity mutation or low affinity mutation. 6:07 Now if they have low affinity mutation, these now central sites, they cannot 6:14 recognize the 6:15 antigen anymore because they are affinity for these antigens have decreased. 6:21 And so they are not needed by the body and so they die through apoptosis. 6:24 However, if a central blast moving into this light zone has a high affinity 6:30 mutation, it 6:31 means that this central blast now central site has a higher affinity for these 6:36 antigens and 6:37 so it can recognize it. 6:38 And if it recognizes it, the T helper follicular cells within the light zone 6:46 will then bind 6:47 with this central site and send signals to it, send cytokines to it, to cause 6:54 it to undergo 6:55 class switching, differentiation and proliferation. 6:59 So the high affinity B cells proliferate, and then they will class switch. 7:05 The low affinity B cells will die through apoptosis. 7:09 So this high affinity central site can differentiate and class switch to either 7:16 a memory B cells, 7:17 which typically have an immunoglobulin G antibody. 7:21 And the memory B cells, they form memories of that particular antigen. 7:27 Alternatively, this central site can differentiate and class switch to plasma 7:32 cells, which have 7:32 different types of immunoglobulin antibodies. 7:36 And the plasma cells role is to create antibodies. 7:39 So what are antibodies? 7:40 What do they do? 7:41 Well, they do three main things. 7:42 Let's just recap. 7:43 First of all, antibodies can neutralize a pathogen, basically preventing it 7:47 from it, preventing 7:48 it to adhere to other types of cells. 7:51 There's also obstinizes a pathogen, which promotes phagocytosis, basically, 7:57 helps phagocytes 7:59 engulf these pathogens more easily. 8:02 Antibotis also activates the complement proteins, which, if you remember, 8:06 complement proteins 8:07 essentially help destroying and stimulating or promoting phagocytosis of the 8:12 particular 8:13 pathogen. 8:15 It helps destroy the pathogen by forming a, what's called the membrane attack 8:19 complex, 8:20 which causes the pathogen, or bacteria, in this case, to lyse, to burst by 8:24 itself. 8:25 Now, we will not follow the memory B cell, but we will follow the plasma cell. 8:30 This plasma cell is a long-lived plasma cell. 8:33 So let's go back to the big picture here. 8:36 So the image of B cell goes, undergoes maturation into plasma cells, long-lived 8:41 plasma cells. 8:42 And these plasma cells will travel into the lymph vessel. 8:45 So in this diagram here, as you can see, we have the long-lived plasma cells, 8:49 as well 8:49 as these other activated T cells, the T killer and the T helper cells, leaving 8:54 the lymph node 8:55 via the lymph vessel, via the efferent lymph vessel here. 9:00 So traveling out of the lymph node via the efferent lymph vessel, we have 9:04 plasma cells, 9:06 we have T killer cells, and many type of T helper cells. 9:10 So these T helper cells will travel to the site of inflammation, infection, 9:15 infiltration. 9:17 The plasma cells can also travel to the tissues, however, they usually travel 9:21 to the bone marrow. 9:22 And in the bone marrow, that is where they will secrete its antibodies. 9:27 And that's for the next video. 9:29 Thank you.
