Immune Response

00:01 We can divide immune responses into innate responses and adaptive responses.

00:06 and these have particular characteristics.

00:08 So, you may be wondering what the difference is between the innate and the adaptive response? Well, I'm going to tell you.

00:16 Innate immune responses have a very broad specificity for what we call pathogen- associated molecular patterns.

00:26 deviated to PAMPs, P-A-M-P.

00:29 Pathogen-associated molecular patterns.

00:32 This is in contrast to the adaptive immune response, which has a very high degree of specificity for what we refer to as antigen.

00:41 Antigen is essentially anything that can be recognized by the adaptive immune response.

00:47 The innate response lacks a type of immunological memory seen in the adaptive response and often exhibits a similar intensity upon re-encounter with the same pathogen.

01:00 However, in some cases, it may mount an enhanced response when meeting the pathogen again.

01:07 A phenomenon known as trained innate immunity.

01:12 We talk about the primary and secondary immune response.

01:16 This is due to something referred to as immunological memory.

01:21 And we will learn a lot more about immunological memory later on in these lecture series.

01:29 And then, finally, the innate immune response is a rapid response.

01:35 It occurs within minutes or hours.

01:37 It's very quick.

01:38 The cells already present in the body tissues, or are recruited directly and very quickly from the blood circulation.

01:47 So, you can happen very, very soon.

01:49 In contrast, the adaptive immune response is initially rather slow to get going.

01:55 It takes a few days before it really gets off the ground and is fully effective.

02:01 And this is because the cells need to proliferate.

02:04 They need to expand up in number in the secondary lymphoid tissues.

02:10 So, on the left hand side here, you can see that the innate immune response cells alive are already in the tissues at the bottom there on the left, you can see a tissue macrophage.

02:25 Already sitting in the tissues lying in wait, in case an infection comes along.

02:30 And above that, you can see the multi-lobed neutrophil cell that is leaving a blood vessel and entering to go to the place where the infection is present in the tissues.

02:45 In contrast, for the adaptive immune response, you need cell proliferation to occur in the secondary lymphoid tissues.

02:54 As we've already heard, this can take several days to curve fully.

02:59 And then those cells, once they have proliferated and become activated, can leave the secondary lymphoid tissues, and then themselves go to the location where the infection is present.

03:13 So one thing that should already be coming quite clear to you actually is that the immune system needs to detect that there is a threat.

03:22 It needs to recognize the enemy.

03:25 The immune system is there to attack harmful pathogens.

03:30 A pathogen, something that generates pathology, something that is going to cause disease.

03:36 So the immune system needs to be able to detect these harmful pathogens.

03:43 But there are many things that the immune system should not respond to that we don't want it to respond to.

03:50 It does not attack our own healthy body components.

03:54 What? Immunologists refer to as self.

03:59 Also, we've already mentioned the beneficial commensal microorganisms, or microbiota, as they're often called.

04:07 These also should not be attacked.

04:11 Also, food antigens.

04:13 You probably had something to eat already today.

04:16 You don't want to attack the antigens that are present in the food and so forth.

04:20 So there are many things that the immune system should not attack.

04:24 But there are other things that are harmful, that the immune system does need to mount a response against and eliminate from the body.

04:33 So how does the immune system actually detect that there's a threat? Well, it has a number of different molecules that we refer to as receptors.

04:46 And one important group of receptors are the pattern recognition receptors.

04:52 These are sometimes also referred to as pathogen recognition receptors.

04:56 I'm afraid as you'll see, there are many alternatives terms that are used in immunology for the same thing.

05:03 Pattern recognition receptors, pathogen recognition receptors.

05:07 They both have BVA to PRR.

05:09 And they both recognize what are referred to as Pathogen-associated molecular patterns or PAMPs.

05:18 That are molecules that are present either on the surface of pathogens or sometimes inside pathogens.

05:24 So, pattern recognition receptors recognize pathogen associated molecular patterns in order to determine that there is a threat that needs to be responded to.

05:38 And the pattern recognition receptor will bind to the pathogen associated molecular pattern.

05:45 And this will result in a signal being sent into the cell of the immune system, and it will become activated and begin to mount an immune response.

05:56 As well as recognizing pathogen associated molecular patterns or PAMPs.

06:01 Pattern recognition receptors can also recognize damage associated molecular patterns.

06:07 So, maybe you're wondering what's the difference between a DAMP and a PAMP? Well, a DAMP is something that is produced by our own body.

06:16 These Damage-associated molecular patterns are produced by our own cells, when they become damaged.

06:23 Whereas, Pathogen-associated molecular patterns as the name indicates, are present either on the surface or within pathogens.

06:34 And just like the pattern recognition receptors bind to pathogen associated molecular patterns, so, they can bind to the damage-associated molecular patterns.

06:48 In contrast, the cells of the adaptive immune response have antigen-specific receptors.

06:55 So, in general, cells the innate response have these pattern recognition receptors.

07:01 Whereas, the cells of the adaptive immune response have antigen specific receptors.

07:05 In actual fact, is a little bit more complex than that, because we now know that cells of the adaptive response also have pattern recognition receptors as well as the cells of innate response.

07:16 That the major way in which cells of the adaptive-response recognize engine is using antigen specific receptors.

07:26 And they will bind to the pathogen using these receptors, as you can see here.