Main content
Health and medicine
Course: Health and medicine > Unit 13
Lesson 7: HIV and AIDS- What is HIV/AIDS?
- What is HIV and AIDS?
- Transmission of HIV
- How HIV infects us: Mucous membranes, dendritic cells, and lymph nodes
- How HIV infects us: CD4 (T-helper) lymphocyte infection
- How HIV kills so many CD4 T cells
- Diagnosing HIV - Concepts and tests
- Treating HIV: Antiretroviral drugs
- HAART treatment for HIV - Who, what, why, when, and how
- Defining AIDS and AIDS defining illnesses
- Immune reconstitution inflammatory syndrome (IRIS) in AIDS
- Preventing an HIV infection
© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice
How HIV infects us: Mucous membranes, dendritic cells, and lymph nodes
Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content.
These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Vishal Punwani.
Want to join the conversation?
- Are dendritic cells only located in mucous membrane?(3 votes)
- Dendritic cells are all over the place! They act as the sentinels that alert the immune system to a potential intruder. Imagine the dendritic cells to be in highest concentration wherever our bodies come in contact with the outside world. In the layers of our skin, mucus membranes, and along the entire lining of our gastrointestinal tract (from mouth to bottom). They also live in our lymph nodes and spleen, and look for intruding pathogens in our blood.(7 votes)
- Do all HIV sufferers have eczema? What symptoms does AIDS have?(3 votes)
- the symptoms are getting sick a lot easier, coughing, up blood if the aids gets really bad. i AM NOT AN EXPERT. just to let you know hope you you liked my commit.(1 vote)
- Are there blood vessels in the mucous membranes?(2 votes)
- Yes and they are generally capillaries (the smallest blood vessel). Blood flow is important for delivery of cells and nutrients to the mucosal site. Cells arrive via blood vessels, however they leave via lymphatic capillaries which drain into the lymphatic system, which is related to but separate from the circulatory system.(2 votes)
- But what about Natural Killer Cells? Shouldn't they be able to deal with the infected?(1 vote)
- Macrophages, B cells and dendritic cells, present foreign antigens to helper T cells. Cytotoxic and Helper are responsible for telling the immune system what to do when Antigen Presenting Cells present on the major histocompatibility complex-because it's the CD4 that's become infected, HIV is evading the immune system and depends upon apoptosis of the CD4 alone, I believe.(1 vote)
Video transcript
- [Voiceover] How does HIV
actually infect our cells? What exactly happens when
you get an HIV infection? Well, to find out, let's
follow a little HIV particle, an actual virus, through what it does and where it goes in
order to infect a human. So let's start by drawing some skin here. Actually, let's say
this is mucus membrane. So the soft, most areas
not quite protected like everywhere else on your body that's covered by normal skin. So you'd find these mucus membranes inside your mouth or in your throat or your noes our inside the vagina or at the tip of the
penis or in the rectum, or anywhere in your
digestive tract, really, any and all of these are mucus membranes and remember, this is relevant, because the most common
way HIV is spread is by sexual contact, which is when these areas
or some of these areas are likely to come into contact with infected sexual
fluids from each other. And, just to jog your memory, remember the second most common way HIV is spread is when it's directly put into your blood from an unsafe needle or from blood to blood contact with
an HIV infected person. And, you know, we can
sort of intuitively see how HIV can attack our white blood cells like our CD4 T helper
cells or our macrophages when it's directly put
in the blood stream. That bit's a little obvious. But what's less obvious is how HIV gets into our bodies across our
mucous membranes, right? I mean, they look like barriers to me. Well, it turns out that we have these really interesting
little immune system cells imbedded within and throughout our mucous membranes. And these are called our dendritic cells. And these cells are really quite key in HIV infection. What they do is they
protrude their little limbs, essentially up to the surface
of our mucus membranes because their job is to sort
of sample the environment to look for bacteria or
viruses or any other threats to our health. And practically speaking, what they do is they sort of continually
grab on to particles that they find sitting on
top of our membranes here and they pull them in across the membrane to check them out to
see whether they found a good reason to activate our
immune system or not, alright? They actually have the ability to kick off a pretty big immune reaction depending on what kind of particle they've found. So what they do in a normal scenario is that if they find something
they're worried about, maybe a virus or a bacteria
or something like that, they internalize it and
then they kind of cut it up into a few pieces and then they display little pieces of it which, at this point, are called antigens on their surface, because essentially they wanna get other immune cells attention. They're essentially saying,
"Hey, guys, look what I found! "Let's make some immune cells
that our targeted to these "little pieces here, let's
wipe this thing out." And really, really, really importantly, while they're doing all of
this, all of this break down and displaying of
foreign invader antigens, they're also on the move. They've sort of picked up shop and they're already on their way through the blood stream, or
through the lymphatic system on their way to one of
our many lymph nodes. They usually go to the closest one. Lymph nodes, by the way,
are a really important part of our immune system where
a lot of our immune cells, particularly our lymphocytes, hang out and sort of filter through our body fluid for any pathogens that they might need to become sensitized to and respond to. You can think of these lymph nodes as police stations where a lot of our cops hang out waiting to be briefed on their next task, to
be shown wanted posters, so to speak. This is standard practice
for our dendritic cells, by the way. The normal sort of every day life for these guys goes something like they hang out in the mucousal surface, they find pathogens, they carry them to the lymph nodes to
alert the lymphocytes. This is just a normal day
for them at this point. The problem with HIV though is that it's not quite like
the other pathogens, either bacteria or viruses. I mean, some of it gets degraded, right? Chopped up and displayed
to the lymphocytes and the lymph nodes here, sure. But some of the HIV
actually gets transmitted to the lymph node in tact which is no good. And I'll tell you how that happens. There's three sort of main ways that our dendritic cells
sort of misguidedly bring intact HIV to our lymph nodes. One way is by what's called
an infectious synapse where there dendritic
cell essentially grabs on to HIV particles
using its plasma membrane and then a protein on its plasma membrane and it essentially carries
it, just like this, to the lymph node and then it sort of hands it off, hands off
the little HIV particle to a T-cell to deal with, which usually results in that
T-cell becoming infected. Another way is where the
dendritic cell endocytosis a group of HIV particles, bring that endocytosed
group to the lymph node and then exocytoses them
right inside the lymph node where all you other immune
cells get exposed to them and can thus get infected as well, right? Not very thoughtful of the dendritic cell to do that. And the third way is that
HIV will directly infect our dendritic cell at some point during initial contact
either at the mucus membrane or during the period of
time when the dendritic cell is traveling to the lymph node. And throwing an infected dendritic cell into a lymph node is
generally a terrible idea, probably the worst idea
anyone could ever have, because after becoming infected, the dendritic cell will start pumping out copy after copy after
copy of HIV particles that are just as infectious
as the first one. But, you might be wondering, well, how does infection of
an immune cell by HIV result in more copies of HIV being made? And that's a great question and that's actually the standard way that viruses work. They sort of highjack
our cellular machinery and they use it to create lots and lots of copies of themselves that can then sort of leave the infected cell and go on to infect more of our other cells to sort of repeat the whole process. HIV though, it sets itself apart from almost every other
virus because the way it does this highjacking is a
little more different and a lot more sneaky than other viruses. And I'll cover how it
highjacks when we look at how HIV particles infect
their preferred targets, our T-helper cells.