Type I Hypersensitivity: Manifestations

00:00 So what are the manifestations of IgE antibody mediated disease? Well, it can be everything from things that are merely annoying.

00:08 Such as seasonal rhinitis, to things that are much more serious, such as food allergies.

00:15 Responses such as urticaria or Hives.

00:18 Kind of very scratchy, irritating, mast cell degranulation within the skin.

00:26 Asthma with bronchoconstriction and even anaphylaxis.

00:30 So those are all manifestations and it can be from merely annoying all the way to fail, in terms of how many mast cells are being activated at once.

00:40 And for things like food allergies and anaphylaxis, we have systemic mast cell activation.

00:46 For seasonal rhinitis, it's only in your nasal passages.

00:51 So you can see that these can cause a significant amount of disease and pathology.

00:56 So let's look at just how this might play out at a histologic level.

01:01 On the left hand side is normal lung.

01:04 The brighter pink rim things are going to be the normal bronchioles.

01:09 And there isn't any inflammation, there's no increased mucus production, the airways themselves are open.

01:16 And that's the way it should be.

01:19 On the other hand with asthma.

01:21 Now, because of mast cell degranulation causing bronchoconstriction, because of the cytokines causing now the production of increased mucus, we are getting tight little airway surrounded by lots of inflammatory cells.

01:35 And we have increased mucus production.

01:37 And this poor patient can't breathe.

01:40 They're trying to suck air on little tiny straws that are filled up with mucus because of the action of the mast cells.

01:52 So that was all IgE type 1 hypersensitivity.

01:57 Immediate type hypersensitivity.

02:00 Now let's talk about non IgE antibody mediated diseases.

02:03 And this is going to be kind of as a ramp up for the next little talk that we're going to have together.

02:09 Again, once we understand the toolkit of how the immune system works, and how the mediators are elaborated, all this just falls out as predictable.

02:19 So if we have antibody that binds to a particular tissue, then we'll get complement activation, and we'll get cell lisis of whatever that antibody is bound to via the membrane attack complex generation.

02:33 Okay.

02:35 We will also have the formation of C3b, and antibodies that are bound with rearrangement of their Fc component that will allow opsonization.

02:47 Basically, whatever the antibody or complement is bound to is now tasty.

02:51 It's opsonized.

02:52 And phagocytes, who have the appropriate receptors will come up and try to eat it.

02:57 Now, they may be able to eat individual cells.

03:00 Well, talk about diseases such as autoimmune hemolytic anaemia, where the macrophages can actually eat an entire red cell.

03:07 However, macrophages that are trying to eat an entire basement membrane will actually not be able to do so because they can't get their pseudo pods around it.

03:18 And then we'll have frustrated phagocytosis.

03:21 Meaning the macrophage is trying to eat and it's trying to bring in lysosomes to digest whatever it's eaten and now it's going to dump that lysosomal content onto the surface of whatever big thing it's trying to eat, such as a basement membrane.

03:38 Other antibody mediated diseases includes immune complex deposition with complement and phagocyte activation.

03:46 And immune complexes, again, are a type 3 hypersensitivity response.

03:52 And sometimes antibodies can block or stimulate receptors in a variety of tissues.

03:59 And so we'll talk about those in the coming lecture next.