 This one here is a very bad bacteria. This bacteria there to enter my body. But my body is gifted with a very strong immune system. We humans are gifted with a very, very strong immune system. And what our immune system does? The first thing our immune system does is that it recognizes. Recognize the foreign invader in this case a bacteria and then produces weapons specific for that foreign invader. So it will produce you can say customized special weapon against this bacteria which we call antibodies. So this antibodies are made specially for this bacteria. So now this antibodies will go and bind to this bacteria and then call more immune cells and finally kill this bacteria. So this bacteria will be eventually killed. But that is not the end of the story. Our immune system future proves us from this bacteria. It prepares another special type of cell called the memory cell. This is very, very important. This memory cell now will stay in our body and will fight this bacteria if it dares to enter our body again. We will talk about this memory cell in a minute. But before that, let me tell you that our immune system initially had no idea what this bacteria was. But once this bacteria got inside our body, our immune system tried to recognize or understand parts of this bacteria and it produced antibodies against it. So we are not born or our immune system are not born with the knowledge of this foreign invader, this bacteria. But during our lifetime as our immune system comes in contact with the new, new foreign invaders like bacteria, viruses, it adapts itself to produce immunity towards those foreign invaders and therefore this type of immunity is called adaptive immunity. Now I want you to imagine a situation in which your friend Ram as he was going back to home from school was bitten by a snake and now you just saw that. What will you do? You will probably rush him to the hospital where the doctor will give him some anti-venom shots. Now my question is just like the bacteria, this venom of the snake, let me write it again, the snake venom is also a foreign substance for the body and just like our immune system worked against the bacteria, our immune system should also work against the snake venom, right? So why do people panic during a snake bite and why do we rush to hospital and we are given anti-venom shots? Well the answer to this lies in the time that our immune system requires to function. So here is a graph. The x-axis gives the time and the y-axis gives the antibody amount in your body at any point in time. Now as you can see, this is the first exposure. Let's talk about bacteria. So this bacteria backed, entered the body and this is the first day of exposure and as you can see our immune system took some time to react to this foreign particle. So it took around 4 to 7 days just for our immune system to recognize this foreign particles and produce antibodies against this foreign particle. But if we wait that long in case of a snake bite, a person will die and the reason is snake venom are very potent, it works very fast. Unlike bacteria, they also need some time to create havoc inside our body and that time is utilized by our immune system to create weapon against the bacteria. But in this case, the snake venom is very potent. It won't give our immune system any time to prepare any weapon against them and therefore we need to take anti-venom shots. Now do you know what these anti-venom shots contain? These anti-venom shots are nothing but antibodies against that snake venom. Now where do doctors get these antibodies against snake venom? Because we saw our immune system produces specific antibodies against a specific foreign invader, right? So where did the doctor get specific antibody against snake venom? They get it by injecting the snake venom into horse or some other mammal. Generally, horses are used because it is seen that horses could quite resist the effect of snake bite. So once the snake bites a horse, the immune system in the horse body produces antibody. Those antibodies are extracted and stored as anti-venom shots. Interesting, right? Now in case of the snake bite as we just saw, we got the antibodies from outside. So the kind of immunity that we received by the introduction of antibodies from another person or animal is called passive immunity. Because here we didn't produce our own antibodies. So you can already guess what this kind of immunity is called. The immunity in which our body produces our own antibody and memory cells. I'm sure you have probably guessed it by now. This is called active immunity. So let me write down active immunity. Now apart from the difference of producing our own antibody in case of active immunity and introducing external antibody in case of passive immunity, what other differences can you spot between these two types of adaptive immunity? Just pause the video for a second and think about it. Alright, so the first difference that I can spot is this memory cell. In active immunity, we get memory cells. Our body produces memory cells. But there is no question of memory cells in case of passive immunity. Because here we have introduced antibodies from outside. So there is no question of memory cells. So let me write down that in case of active immunity, memory cells are produced. But in case of passive immunity, no memory cells are produced. Okay, now these memory cells are important because if that foreign invader gets inside the body again, our body has a weapon to fight against it. But in case of passive immunity, let's say your friend Ram was attacked by a snake again. He will have to take the anti-venom shots again, right? So in case of passive immunity, there is no memory. So there is no weapon left that could recognize the foreign invader that have attacked the body previously. So this is the very first difference, having memory cells and not having memory cells. And the next difference lies in the time of action. So let me bring in the graph again. So let's first discuss about active immunity. This is the first day when the foreign invader entered the body. And this is the number of days our immune system took to act against that foreign invader. So it took around four to seven days. But in case of passive immunity, the day the venom entered, the same day the anti-venom shots were given that had antibody readily made that can go and bind to anti-venom and destroy those anti-venoms, right? So which of the two is faster? Passive immunity, right? Because as soon as the anti-venom shots are given, it will go and destroy the snake venom. But in case of active immunity, our immune cell took quite some time to act against the foreign invader. So active immunity is comparatively a slow process. Whereas passive immunity is comparatively a fast process. Now I like to remember active immunity as home cooked food and passive immunity as ordering food from outside. So you must be thinking why is she making this weird comparison? This is just a trick to remember, okay? So passive immunity means ordering food from outside. So how do I relate? When you order food, you get the order really very fast. But if you cook food at home, you have to give a lot of time to cooking, right? So when you cook food, it is slow. It takes a lot of time to cook food. But if you order food, it's very fast. The delivery happens within minutes. And again, if you order food, you will not know how that food is cooked. So the next time you want to have the same food, you will have no option but to order again. So there is no memory of how that food is cooked. Because there is no question of memory here, right? Because the food is not cooked by you. But in case of active immunity, as you have cooked your own food, you will know how that food is cooked. So the next time you want to have the same food, you can cook it yourself. Okay. So active immunity, we will compare it to home cooked food. And passive immunity is ordering food from outside. All right. I'll give you an example of adaptive immunity. And how about you guess whether it is an active adaptive immunity or passive adaptive immunity? All right. So the example is of vaccination. What do you think vaccination is? Because vaccination provides immunity, right? So what do you think? Is it an active immunity or passive immunity? Let's find out. So in order to find out, we need to know what we inject actually in case of vaccination. So in a vaccine, we actually have non-infectious part of a harmful pathogen. So if this vaccine is against a virus X, then this vaccine will contain either parts of this virus X or this virus is dead and the entire dead virus is used in it. Or this virus is somehow made non-viral length. That means made non-infectious. And those viruses which are non-harmful are administered into the human body. Now, why do we do that? We do that to introduce our immune cells to those foreign harmful particles. Now, once our immune cell comes in contact with the virus X, whether parts of the virus X or whether dead virus X or whether non-infectious virus X, our immune cell will immediately recognize it to be something foreign and produce antibodies and memory cells against it. So this memory cell is very important. And this is the reason why vaccines are administered into human body. So that later, when the actual pathogen, when the harmful life pathogen, live virus gets inside the body, there will be memory cells already sitting there in our body that will immediately recognize and fight that pathogen. Now, what do you think? Is vaccination an active or a passive adaptive immunity? Well, since vaccination made our body produce its own antibody and own memory cell, therefore it is an active adaptive immunity. Now, even though these two are the examples of active immunity, there is a slight difference in both the examples. In the first one, the bacteria enter the body all by itself. It happened naturally. So this type of active adaptive immunity is called natural. So this is natural. But here, in case of vaccination, we had to administer it ourselves, right? There was human intervention. So this one is called artificial. So active immunity can be of two types, natural. This type of immunity takes place in every person and we do not need to do anything about it. It happens naturally and it is true for all living organisms or human beings. An artificial active immunity is something in which human intervention is required. But since both these immunities are active immunities, we produce antibodies and memory cells. So even in natural and artificial, if we see, both antibodies and memory cells are produced. Now, just like active immunity, passive immunity also has natural and artificial immunity. So what do you think this is? The anti-venom shot? What do you think it is? Is it an natural or artificial passive immunity? What do you think it is? Well, this is an artificial passive immunity because here human intervention is required and people don't get a natural lead is not true for everyone. So this is artificial passive immunity. Now, how about you think of a natural passive immunity? The definition of natural would be that it is true for every human being. A person do not need to put extra effort in order to get that kind of immunity. So think of an example of natural passive immunity. Now this natural passive immunity is the one that you, me and every one of us have got as a newborn child. We get IgA, which is Immunoglobulin A or we can call it an antibody from our mother through the breast milk. And that provides immunity to the newborn child. So this type of immunity is passed on from a mother to a child. We do not have to put in extra effort in order to get this immunity. So this was all about adaptive immunity. Now you can try and find out more examples and check whether it comes under natural or artificial active and passive immunity.