Immunogenicity of Tick and Other Arthropod Saliva • iBiology

00:00:14.26 Have you ever been bitten by a mosquito?
00:00:19.01 Well, yes, I have been too.
00:00:21.06 Almost everyone around the world has had this experience
00:00:23.05 at least once in their lives.
00:00:25.08 But tell me, have you ever wondered
00:00:27.00 why it's itchy right afterwards?
00:00:29.11 And the answer might surprise you.
00:00:31.24 It's actually saliva.
00:00:33.22 It turns out that, just like you and me,
00:00:35.19 insects like mosquitoes have saliva
00:00:38.05 that they use when they eat.
00:00:40.11 They inject it into our skin,
00:00:42.11 where it numbs the bite so we don't feel the pain.
00:00:44.26 And it makes the blood flow freely,
00:00:47.09 so they can take the biggest meal that they can
00:00:50.14 before flying away... unless this happens.
00:00:54.05 But the itch that you feel
00:00:56.08 is actually our immune system responding
00:00:58.18 to the different molecules in the saliva.
00:01:00.24 And there are many molecules in the saliva,
00:01:04.00 all of which can be classified as
00:01:06.09 proteins, sugars, lipids,
00:01:08.20 and other types of components.
00:01:10.08 Now, a lot of research until now
00:01:11.27 has focused specifically on the proteins,
00:01:14.00 and not a lot of attention
00:01:16.19 has been paid to the sugars.
00:01:18.17 And that is why I was interested in looking at them.
00:01:23.17 Now, I'm going to look at the sugars in the saliva
00:01:26.13 not only of mosquitoes
00:01:29.04 but of all of these bloodfeeders:
00:01:31.03 tsetse flies, ticks, sandflies, and kissing bugs.
00:01:35.14 But why do we care about saliva?
00:01:38.20 Now, the most important reason
00:01:41.18 is that they can all transmit disease.
00:01:43.19 Diseases that can be well known,
00:01:46.01 like malaria, dengue, or sleeping sickness.
00:01:50.14 Because saliva is such an important part of the biting process,
00:01:53.14 it can influence how our bodies
00:01:55.27 respond to these invaders
00:01:58.07 and can have an effect on the success, or not,
00:02:01.14 of an infection in our bodies.
00:02:06.07 The other reason that we could care about saliva
00:02:09.19 is because of the allergic responses
00:02:11.23 that they can induce in some people.
00:02:14.01 And here, I want to tell you a bit more about ticks.
00:02:18.11 But let me first start with a story and a question.
00:02:22.05 What is your favorite food in the whole wide world?
00:02:27.20 For many people,
00:02:29.18 it could be this juicy, delicious, 100% beef burger.
00:02:35.06 Now, imagine taking a bite of this burger
00:02:37.19 and savoring all those delicious flavors,
00:02:40.22 finishing your meal,
00:02:42.20 and going to bed quite happy.
00:02:45.06 And then waking up in the middle of the night
00:02:47.09 feeling not so good.
00:02:49.02 Your body is full of rashes that really itch.
00:02:52.09 Your throat starts to close and your blood pressure drops.
00:02:55.22 You could be experiencing a red meat allergy.
00:02:59.26 And surprisingly enough,
00:03:02.10 the culprit could actually be a tick.
00:03:05.11 Ticks feed differently to mosquitoes and other bloodfeeders.
00:03:11.15 They attach themselves to your skin,
00:03:14.00 where they remain for several days.
00:03:15.28 And during all of this time,
00:03:17.20 they're constantly injecting you with saliva
00:03:20.01 and other molecules.
00:03:22.10 Now, for many people,
00:03:24.12 the bites go completely unnoticed.
00:03:26.08 But for others, it can have life-changing consequences,
00:03:29.02 like the development of an allergy to red meat.
00:03:34.04 The first cases of red meat allergy
00:03:37.02 were reported in Australia around the 1980s.
00:03:40.02 But even many years after,
00:03:41.26 doctors remain puzzled as to why so many people
00:03:45.05 were developing this severe allergic response
00:03:48.08 to red meat.
00:03:49.20 And after a lot of research,
00:03:51.28 they found that what these patients had in common
00:03:54.04 was that they all remembered being bitten by ticks.
00:03:57.12 When they looked at their blood tests,
00:04:00.10 they showed abnormally high levels
00:04:02.17 of an antibody called IgE,
00:04:04.11 which is involved in allergic responses.
00:04:06.29 And in this case, that IgE
00:04:09.02 was specific for a sugar called alpha-Gal.
00:04:12.03 And this was the first suggestion
00:04:15.10 that there was a link between this alpha-Gal,
00:04:17.20 the tick bites,
00:04:19.10 and the allergy to red meat.
00:04:21.19 But this story of discovery doesn't end there.
00:04:24.13 In the U.S.,
00:04:27.05 some patients were reporting really severe allergic reactions
00:04:30.05 to a cancer drug called cetuximab.
00:04:34.05 When they looked at the blood of these patients,
00:04:37.13 they also saw abnormally high levels
00:04:40.16 of these Ig-E antibodies against the alpha-Gal sugar.
00:04:44.12 Now, humans don't produce the alpha-Gal sugar,
00:04:47.20 and that's why our bodies recognize it as foreign
00:04:49.18 and produce antibodies against it.
00:04:52.12 It turns out that the cetuximab drug
00:04:54.20 is produced in a mouse cell line.
00:04:57.10 And because mice do produce the alpha-Gal sugar,
00:05:00.03 the drug ended up being decorated
00:05:02.11 with all of these molecules.
00:05:04.20 And when it was given to some patients,
00:05:06.09 they developed a severe reaction against it.
00:05:09.20 But why only some patients?
00:05:12.16 Well, a bit more digging found out that
00:05:15.18 the patients that developed this severe reaction
00:05:19.14 lived in rural areas of the Southeast U.S.,
00:05:23.01 rural areas where they could be more exposed to the bites of ticks.
00:05:27.14 And so all of this evidence started coming together
00:05:30.25 to suggest and reinforce this strong link
00:05:33.25 between tick bites and the development of red meat allergy.
00:05:40.03 As the condition became more well known,
00:05:42.04 this alpha-Gal syndrome,
00:05:44.01 doctors started to register it
00:05:46.26 in different parts of the world.
00:05:48.08 And in each region,
00:05:50.11 it could be associated with a different species of tick.
00:05:53.14 Now we know that thousands
00:05:56.04 or perhaps more around the world
00:05:58.06 have developed this alpha-Gal syndrome
00:06:00.16 and cannot eat meat anymore.
00:06:02.07 But it's not only beef.
00:06:04.00 They can be allergic to pork, to milk,
00:06:06.01 to the gelatin capsules that surround some medications,
00:06:09.00 and even in some unfortunate cases
00:06:11.28 to life-saving drugs like cetuximab.
00:06:15.20 Now, there's... there continues to be a lot of debate
00:06:20.17 about the source of this alpha-Gal,
00:06:22.14 but some researchers believe that it is found
00:06:25.25 in the saliva of the tick.
00:06:27.17 And this is why these researchers, in Brazil,
00:06:29.24 have decided to explore this connection
00:06:32.04 between the tick bite and the red meat allergy,
00:06:34.14 for the Brazilian tick, Amblyomma sculptum in particular,
00:06:38.23 which is the most commonly distributed in Brazil.
00:06:41.21 So, in order to do this in the lab,
00:06:44.10 they needed to create a model
00:06:46.16 to be able to study the effects of the tick saliva.
00:06:50.26 Because humans don't produce alpha-Gal,
00:06:53.06 they created a mouse model
00:06:55.27 that also doesn't produce the alpha-Gal sugar.
00:06:58.17 They then exposed these mice to tick bites,
00:07:01.05 or to the saliva obtained from these ticks.
00:07:05.22 And when they looked at the blood of the mice,
00:07:07.29 they saw that they produced
00:07:11.00 antibodies against the alpha-Gal sugar.
00:07:13.06 And this was very nice evidence
00:07:15.13 that the origin of the sugar was actually the saliva of the ticks.
00:07:19.13 And at this point, we started a collaboration,
00:07:22.06 where my job was to find the sugars
00:07:25.06 in the saliva of the ticks
00:07:27.24 and confirm that the alpha-Gal was actually there.
00:07:32.09 And first, I want to tell you a little bit about the sugars here.
00:07:36.12 Now, sugars can be also known as glycans,
00:07:39.04 and they are found in all living systems,
00:07:41.21 inside and outside the cells.
00:07:43.29 They can have roles in aspects like metabolism,
00:07:48.12 structure, or cell-cell interactions.
00:07:51.01 And here we see a classic image
00:07:55.00 of the surface of a red blood cell,
00:07:57.19 where all of this fuzz on the surface
00:08:00.01 is actually glycans that are attached to lipids or proteins.
00:08:03.05 And these glycans are the ones
00:08:05.14 that determine your blood group,
00:08:07.03 so they are actually very well known.
00:08:11.02 When sugars are attached to proteins, they form glycoproteins
00:08:14.20 And these are just some types of the structures
00:08:18.18 that you can find attached to proteins.
00:08:20.17 And this attachment can actually
00:08:23.03 influence the protein's folding, interaction,
00:08:25.26 and immunogenicity.
00:08:27.16 And by immunogenicity,
00:08:29.19 I mean the type of strong or weak immune responses
00:08:32.22 that this combination can generate in our bodies.
00:08:37.17 And so, the way that I go about
00:08:40.03 studying the sugars in the saliva of the bloodfeeders
00:08:42.22 is first by extracting their saliva.
00:08:45.24 And so, I can...
00:08:48.06 I have to dissect hundreds of these insects at a time.
00:08:50.23 As you can see here,
00:08:52.16 the salivary glands have been extracted from each of them.
00:08:55.21 I take that saliva into the lab to process,
00:08:59.07 where I treat it with an enzyme
00:09:03.27 that allows me to separate the sugar from the protein,
00:09:06.19 to study each one individually.
00:09:09.05 Now, for purposes of this talk,
00:09:11.04 I'm going to focus on the sugars,
00:09:13.00 because that's what we're interested in right now.
00:09:16.17 I label the sugars with a fluorescent marker
00:09:19.18 that allows me to detect them more easily
00:09:22.09 by liquid chromatography and mass spectrometry.
00:09:28.04 Now, this is the type of result that I would get after that analysis,
00:09:32.18 using ticks as an example.
00:09:35.16 And in this chromatogram,
00:09:37.28 you can see the profile of salivary sugars,
00:09:40.03 where each of the peaks corresponds
00:09:42.22 to a different structure that we now know.
00:09:45.19 But this gives me a very general idea.
00:09:48.26 And after further analysis and treatment,
00:09:51.17 for example with specific enzymes,
00:09:53.19 I can rebuild each of these structures.
00:09:56.17 And here, I am showing you
00:09:59.28 that we found the sugar structure
00:10:02.27 that contains this alpha-Gal,
00:10:04.27 which is this portion that we find here.
00:10:07.17 And so, it's a confirmation that the alpha-Gal sugar
00:10:10.10 is actually present in the saliva of ticks.
00:10:14.18 But now that we know that the sugar structure is there,
00:10:18.17 what is the protein that this alpha-Gal is actually attached to?
00:10:22.23 So, here I turn to the proteins in the saliva.
00:10:26.15 And for example,
00:10:29.16 each of these bands
00:10:32.10 is representing a different protein in the saliva of ticks,
00:10:34.20 and I then purify one of these proteins
00:10:38.05 that has the alpha-Gal,
00:10:40.15 using a marker that is specific for this sugar,
00:10:43.01 as you can see here, that is labeled with the asterisk.
00:10:46.28 I then take this protein
00:10:49.20 and identify it by mass spectrometry,
00:10:51.16 and get a list of candidates.
00:10:55.14 These results, together,
00:10:57.15 help me to confirm that the alpha-Gal
00:11:00.28 is actually present in the saliva of ticks,
00:11:03.15 that it forms part of a glycoprotein,
00:11:06.15 and that knowing the...
00:11:08.17 and knowing this structure can actually
00:11:11.25 help me use these molecules
00:11:14.00 as tools to improve diagnosis
00:11:16.03 or even, perhaps, to create better treatments
00:11:18.17 for the people that are affected by this condition,
00:11:20.22 the alpha-Gal syndrome.
00:11:24.19 But the tick story is only a part of a much larger project,
00:11:28.13 where I'm characterizing the salivary sugars
00:11:31.07 of all of these bloodfeeders.
00:11:33.12 And because we know how important sugars
00:11:36.18 can be to the type of immune responses
00:11:38.26 that saliva can trigger in our bodies,
00:11:43.04 this information will allow me
00:11:46.00 to potentially use each of these structures as a tool
00:11:50.15 to diagnose, monitor, or better treat diseases in different ways.
00:11:55.28 And so, the next time you're bitten by a mosquito,
00:11:58.23 you and I will know what's going on there,
00:12:02.04 in that little bit of skin,
00:12:04.08 all the complex reactions that are being started.
00:12:07.03 You now know that saliva has proteins and sugars.
00:12:11.05 And you know that somewhere around the world,
00:12:13.20 there is one scientist looking at how all of this happens.

This Talk

Speaker: Karina Mondragon-Shem

Audience:

General Public
Educators of H. School / Intro Undergrad
Student
Educators of Adv. Undergrad / Grad
Researcher
Educators

Recorded: June 2019

Talk Overview

Almost every person in the world has been bitten by a blood feeding insect or arthropod, such as a mosquito or tick. Yet, most of us haven’t thought much about arthropod saliva. The molecules found in the saliva of blood feeders play a role in disease transmission and immune recognition. Therefore, it is important to better understand what makes up arthropod saliva. Dr. Mondragon-Shem begins her seminar by describing the phenomenon of red meat allergy, and how it was historically linked to tick bites. She then shares her research findings that confirm the presence of alpha-Gal sugar, the immunogenic molecule that leads to red meat allergy, in tick saliva. Her studies also identified protein candidates that are likely linked to alpha-Gal in tick saliva. Dr. Mondragon-Shem finishes her talk by describing how she has characterized the sugar molecules in the saliva of six species of blood feeding arthropods. This work has implications for better understanding disease transmission and immune recognition.

Speaker Bio

Karina Mondragon-Shem

Karina MondragonShem

Karina Mondragon-Shem completed her Ph.D. at the Liverpool School of Tropical Medicine in the United Kingdom, where she studied the saliva of different blood-feeding arthropods that transmit diseases. Continue Reading

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