so in the previous video we focused on what active immunity was which is the ability to fight off the infection uh or resist the infection but the thing is your body has to do the work so let's look at passive immunity for a bit you see in passive immunity what happens here is the pathogen enters the body but immediately after the pathogen enters the body I just want you to see that the B lymphocyte is sleeping I mean it's not actually sleeping but you know it's inactive so what I'm trying to represent here is the B lymphocytes have not met the pathogen so has immune response happened no it has not but the weird thing is inside our body the antibodies are already present so how's that even possible and the pathogen's quite surprised because wait the B lymphocytes have not responded because when the B lymphocytes respond they're supposed to undergo clonal selection and clonal expansion to produce the plasma cells and memory cells and once the plasma cells are produced that's when the antibodies will be released but in this case there were no plasma cells inside the body however antibodies were already present so that is kind of weird so the question is where did the antibodies come from right so because it could not have come from the B lymoc side because as I've told you the bhoite is inactive it did not respond to the pathogen therefore there was there were no immune response and it's also not due to memory cells inside the body because if it were due to memory cells the memory cells would have had to attach to their antigens through clonal selection so this is quite weird because your body did not have to do anything yet antibodies were already there once the antibodies bind to the antigens um the the fyes are can ingest it and when the fyes ingest it the pathogen is immediately eradicated so did the person fall sick in this case no the person did not fall sick our body was able to respond immediately to the pathogen but again comes the question where did the antibodies actually come from because that's quite a big mystery right as we can see here the B lymphocyst might be like oh this immunity is really amazing because why is this immunity amazing the antibodies are immediately eradicating the pathogen but there are some limitations but let's look at it anyway so from passive immunity the first type of passive immunity we are looking at is natural passive immunity so what exactly is natural passive immunity anyway so let's start with a baby for example like a newborn the baby is just born and in their body they do have B lymphocytes I'm going to use the word B cell uh because you know I don't have enough space to write bosy over there but when I say the word B cell what I just mean is bosy all right and the B cells are inactive they are they are not exposed to any antigens at all so but here's the thing I told you before that in in passive immunity the person's the baby's body does not have to do the work right the immunity happens automatically but how exactly does it happen automatically is the mother the mother breastfeeds the baby and in the mother's breast milk the mother will actually provide antibodies to the baby's body so so you see did the baby actually produce the antibodies no the baby did not produce the antibodies but the antibodies are already present inside the baby that's why it's called passive because I told you in passive the your body did not have to do the work so if you were breastfed what will actually happen is your body will now have antibodies but did you produce them no it was produced by your mother and passed to you and your B cells are still sleeping they're just like yeah I don't know what is going on here the B cells are just inactive in this situation so if a pathogen entered the baby's body and the pathogen wanted to cause an infection the pathogen will not have a chance to do so because the antibodies from the mother will immediately bind to the antigens and it will immediately eradicate the pathogen this is called immediate protection so did the baby fall sick in this case chances are the baby will not fall sick all right so you might be thinking oh wow this type of immunity is amazing because the protection is immediate I don't have to do anything about it you know someone else provides the antibodies to me you know if you're are a lazy if you're a lazy person you're like oh this passive immunity passive immunity sounds good however there is an important condition to passive immunity the important condition here is as follows imagine now the baby grows up and the the the child we don't call it a baby anymore the toddler is now 2 years old and let's say the mother has stopped breastfeeding the child all right here's the weird thing there won't be any more antibodies inside the body because the mother's antibodies will only last for a short period of time so the moment the mother stops breastfeeding the baby or the child the antibodies are no longer that so while there was an infection that happened the first time as I'm circling here in red there were no memory cells produced why were there no memory cells produced because the baby's own B cells did not respond to the pathogen a very important thing I like to remind you is when the mother breastfeeds the child it is only antibodies that are provided to the child the mother's memory be lymphocytes will not enter the child at all that's an important condition to follow so if the toddler who is now 2 years old gets infected by the same type of pathogen 2 years later will they fall sick yes they will fall sick okay because remember it takes some time for the B cells to respond to the pathogen and due to the absence of memory cells the child will fall sick okay and it takes a few days days for active immunity to then kick in so natural passive immunity is just acquiring antibodies from the mother through breastfeeding or the placenta the placenta is just a structure that when the mother is pregnant okay uh the fetus will have this particular structure the fetus is the uh Offspring growing inside the mother's womb and the placenta attaches to the mother and through the mother's uh blood it will will share some of the substances to the fetus and we we when we were developing in our mother's womb uh we would also receive antibodies through the placenta so for the exam you must know that natural passive immunity is acquired through two processes uh one through breastfeeding okay or number two through the placenta that's all we have to know but were you the one who was producing the antibodies no the antibodies were produced by the mother and it was passed to the child so you did not have the child did not have to do any work in this case hence why it's called passive and because the mother is breastfeeding or it happens through the placenta um this is referred to as natural passive immunity that's it but the problem with natural passive immunity is the protection is immediate that is good but the problem is it is shortlived so it only protects the person as long as the antibodies are constantly provided but the moment the antibodies stop being provided there will be no memory cells at all right so the person will actually fall sick in the future so this is called a shortterm or shortlived protection now another type of passive immunity is known as artificial passive immunity so let's just give a situation over here let's call this person person L and person L was infected by pathogens person L can be an adult or a child doesn't matter in this case so when they were infected by the pathogen the pathogen grows inside the body remember if the if the pathogen is infecting your body for the first time usually uh the the the immune response towards the pathogen is quite slow right because you do not have that many B cells we talked about this in the previous video um so usually what happens in between between the immune response time you fall sick it does happen and you develop symptoms now under normal circumstances the B lymphocytes will eventually respond to the pathogen we know this but in some cases it's not always perfect maybe person L is extremely sick maybe they did not have enough nutrients there can be many reasons why these things happen but the immune system is not responding well they're malnourished age factors the immune system is weakened perhaps due to imuno compromise like due to conditions such as AIDS or sometimes even leukemia by the way so their immune system their B lymphocytes were supposed to respond after a few days but the B lymphocytes are not responding towards the pathogens so in this case over here um if it's not responding um if we were to give it a few few more days the person might die okay because the pathogens might spread throughout the body and just cause so much damage in the organs that the person may not be able to recover and they might die from this infection waiting for the immune system to respond is not a good idea in this case under normal circumstances if the person was generally fine we could wait for the immune system to kick in and respond to the pathogen uh like for example in active immunity but in this case we waiting for the active immunity to kick in might be deadly for person l so in this case what we have to do is we have to provide person L with antibodies then you might be thinking where do we get the antibodies from without going into the detail of this let's look at person M person m is a uh is a particular uh individual who has immunity against the pathogen and because they have immunity against the pathogen they can produce antibodies so which means to say if the pathogen were to infect person M they will not fall sick because they can immediately release antibodies and eradicate the pathogen what we can do is we can actually take antibodies from person M and those antibodies are then injected into person l so this is like for example like blood transfusion when you can donate blood you can also donate antibodies from one person to another it's called Uh imunoglobulin therapy but you don't need to memorize that so here's the thing so person L receives antibodies he did person L produce their own antibodies no the antibodies were given to them through someone else okay the antibodies from someone else were provided to them and when those antibodies which were obtained from someone else were given what was actually happen is these antibodies will immediately bind to the pathogen and it will get eradicated but look at person else immune cells the B cells did they respond to the pathogen no they are still sleeping or inactive so even though the infection happened there were no memory cells produced because the person's own B cells did not respond I use the word the baby's own B cells over there but just put it as the person's own B cells did not respond in that case so in this situation over here artificial active immunity is acquiring antibodies from another person and let's say 2 months later person L uh gets infected by the pathogens again will person L fall sick yes they will fall sick because they do not have memory cells uh because their own immune cells did not respond to the pathogen so they might fall sick in the future so the protection is shortlived or shortterm because it only protected the person at that point of time it does not protect the person in the future so passive immunity is pretty fantastic because the protection is immediate the antibodies are like given um almost instantaneously but the only issue here is there were no memory cells that were produced at the end of it so because you did not not produce memory cells if the same type of pathogen infects you in the future you will fall sick again that is the problem with passive immunity so coming back to Natural passive immunity the mother provides antibodies to the child through the breast milk or placenta and the baby for example the newborn baby or the toddler will have antibodies in their body look at the antibodies it's already present as I've highlighted over there so if the pathogen th to enter the body the pathogens are immediately eradicated because those antibodies can bind to the antigens and you know that basically happens but let's say one year later if that child is infected look at one year later the child was no longer breastfed so will they have antibodies in their body no they will not have any more antibodies are they protected against the same type of pathogen no they are not technically so if the pathogen enters the body in the future they will fall sick they will have to fall sick their own B cells will have to respond undergo clonal selection clonal expansion you know produce the plasma cells that's going to take time basically and in artificial passive immunity let's say the person falls sick due to the pathogen uh they go to the hospital and antibodies are infused or injected into their body so the antibodies are provided immediately the antibodies will immediately bind to the anen and eradicate the pathogens so the point here is as I've highlighted in pink mother provides antibodies and and antibodies are infused so the antibodies are obtained from an external Source natural being your mom artificial being the donor or a person who donates the antibodies to you the important thing to understand here is through passive immunity the protection is immediate but the your only own body undergo the immune response no as I've highlighted your B cells there your B cells are still sleeping they did not know what the hell was going on at all so because your B cells did not undergo the immune response you did not produce memory cells so this protection that happened earlier was shortterm and it only happens as long as you're given antibodies but in the future if you no longer have antibodies that are provided to you you will fall sick if you get infected by the same type of pathogen so some students are still going to be like uh I still don't kind of understand this okay let's look at another situation now the situation over here don't need to memorize the situation by the way but this person is very sick due to an infection so in their body there are too much pathogens causing harm now if you are the doctor in that situation you have two choices for the patient Choice number one you wait for their own lymphocytes to respond Pro clonal selection or Choice number two you inject the person with anti bodies right so but Choice number one has its own problems the problem is if you're going to wait for the person's immune system or the lymphocytes to respond it will take a few days and in that time the person might die so it really depends on the um condition of the person if the person is extremely sick and organs are starting to fail uh Choice number one may not be a good choice but the advantage of choice number one is if the body does undergo the immune response clonal selection will be succeeded by clonal expansion and it will produce plasma cells and memory cells and because of uh plasma cells the person will release their own antibodies and because of memory cells it will provide long-term term protection so the memory cells produced to provide long-term protection in the future and choice number one is referred to as something called natural active immunity but let's say the doctor decides not to wait and let's say the doctor decides to inject the person with antibodies instead because maybe the person had one foot in the grave already the doctor was thinking hm if we waited if we follow Choice number one the person might not actually recover the person might actually die so by switching to Choice number two the doctor decided to inject the person with antibodies and the antibodies will immediately bind to the antigens of the pathogen and the fyes will ingest it we talked about this in the previous videos so the advantage here is the protection is immediate so the patient recovers from the infection and it quickly destroys the pathogen the disadvantage is the person's own immune cells did not undergo the immune response so were memory cells produced no so they can get reinfected in the future for Choice number one the advantage is if the person gets reinfected in the future they they will not fall sick but for the choice number two they might fall sick in the future again and this type of immunity is referred to as artificial passive immunity passive because the antibodies are given to the person artificial because it was injected not from the mother to the child now another very important thing I would like to remind students is that some students when I ask the question I show you the situation again this person is very sick due to an infection right they already have pathogens in their body the pathogens are causing harm some students will immediately say why can't I give vaccines to this person you do not give vaccines to a sick person oh my God please do not do that that is the equivalent of a person coming to the clinic or the hospital and they are already bleeding like you know they're bleeding due to an injury and the doctor pokes them even more or just basically stabs them and makes them bleed even more they're like oh you're bleeding a little bit look let me make you bleed a little bit more no you don't do things like that you do not give vaccines to sick people okay that's making it worse because what are vaccines vaccines contain dead p pathogens and antigens only so if you vaccinate the person who is already sick you are adding more foreign substances into the person's body and you might actually just kill the person okay in that case you do not give vaccines to sick people please please please please please remember that okay it's it's quite a common mistakes that students make by the way so do not do that at all so in a healthy person for example okay uh let's say this person is healthy but there's a pandemic going on okay um they want to be protected from the pathogen so as you can see the pathogen over there it's infecting many people and those people are running away from the pathogen so this person over here is healthy they have not gotten sick yet but they want to be protected from that particular pathogen in that case what you can do is you can inject the person with vaccines so the vaccine which contains the dead pathogen or the antigens uh will bind um it will enter the person's body but will it cause the infection will it make the person sick no it won't because the vaccines are just dead pathogens or antigens unable to cause the infection so those antigens will then eventually meet up with these specific B lymphocytes okay and as you can see that clonal selection is taking place clonal selection will uh then be followed by clonal expansion the person produces plasma cells and memory cells and because of memory cells the person will now have long-term protection so that same person let's say they're walking around in public and the pathogen tries to infect them will it cause them to fall sick no because the vaccines have now protected them and because of the memory B cells they can respond immediately to the pathogen and they will not fall sick this is an example of artificial activ immunity immunity active immunity because you yourself produce the memory cells and the antibodies artificial because we deliberately put the antigens and the pathogens into your body we wanted the pathogens and antigens to go into your body so that it tells your immune cells to produce the necessary memory B lympocytes so these are the differences between active and passive immunity that you must know active immunity has its own advantages passive immunity has its own advantages it depends on the situation