In the last video, we
talked a little bit about the immune system. In that video, we focused on the
nonspecific or the innate immune system. So let me write that. And even in the nonspecific
immune system, we subdivided that into kind of the
first line barriers. And those were things like the
skin, or the stomach acid, or the acidity of the oils on
the outside of your skin. These are just natural barriers
to not allowing things inside of your body, but
then once they get in-- so you can almost imagine
these were the first line of defense. And then you had your second
line of defense, but these are still nonspecific-- and when we
say nonspecific, it means that they don't necessarily know
what type of virus, what type of protein, what
type of bacteria. They just know that this
thing looks shady. Let me eat it up. Let me kill it. Let me have an inflammatory
response. So in there, we said, well,
there's an inflammatory response, which I'm actually
going to talk about after we do videos on the specific
immune system. You have your inflammatory
response, which really just gets things to where the action
is at and then you also have your phagocytes, which
are these cells that are engulfing things. And just so you know, all the
phagocytes that we talked about in the last video, these
are all instances of white blood cells or leukocytes. These phagocytes right here,
these are all-- I talk about dendritic cells and macrophages
and neutrophils. These were all white
blood cells. These weren't all the kinds
of white blood cells. We're about to talk about more--
and the other word for white blood cell is
also leukocyte. So that is nonspecific. Well, one, it just doesn't let
you in, but then when you're in, it says, hey, you're
just shady. I'm going to eat you up. I have receptors. You have some double stranded
DNA floating around. Only viruses have double
strand DNA. I'm going to eat you up. I don't know what type
of virus you are. I don't know if I've seen
you before or not. That's why it's nonspecific. Now the really interesting
thing about our immune system-- and this nonspecific,
this exists across many, many, many species and types of
organisms. But the specific is kind of a-- it's thought to
be a newer adaptation. What I'm going to talk about is
the specific immune system that's particular to humans. That's our other
classification. Let me do it like that. So then you have your specific--
or you can imagine it's an adaptive
immune system. You've probably heard
of things like that. I have resistance to that
bacteria or that virus. So this is adaptive. And it's really all based on
having exposure to things. And within the specific immune
system, we talked a little-- when we talked about the antigen
presenting molecules that phagocytes do-- that
plays a role in this. We're going to go into more
detail, but I don't want to confuse you. But the main actors here are
called lymphocytes, not to be confused with leukocytes--
because they still are leukocytes. So let me write this down. These are specific. Phagocytes, for the most part,
are nonspecific, but both of these are white blood cells. Lymphocytes are another
type of white blood cell or leukocyte. Don't want to confuse you with
this convoluted diagram, but I just want to make the
terminology clear. When someone talks about a
white blood cell, they're really just talking about a set
of cells that when people first tried to separate the
components of blood-- you'd have your red blood cells that
would kind of settle in the bottom, then you'd have this
layer of white frothy stuff in the middle that was really made
of white blood cells, and then on the top, you had the
fluid, the plasma from your blood, kind of the
watery part. So that's where the name came
from, but they have different roles, but they interact
with each other. Now lymphocytes can be divided
into B lymphocytes, usually referred to as B cells--
and T lymphocytes. And the B and T just come from
where they're developed. B lymphocytes were first
recognized in the bursa of Fabricius. That's why it's called B. That's actually a part of birds
that participate in the immune system. And so the B came from bursa,
but B also applies to the human immune system because it's
produced in bone marrow. So that might be an easier
way to remember. It's produced in bone marrow. It's developed in bone marrow,
but historically, the B came from the bursa of Fabricius,
just in case you want to know. But it's easy to remember. The B could also stand for bone
marrow because that's where it's produced. T lymphocytes actually do start
off in the bone marrow, but they mature and become what
they are in the thymus. So that's where the
T comes from. Now in this video, I'm going
to focus just on the B lymphocytes-- because frankly,
if I focused on everything, it would be an hour-long video. But the B lymphocytes frankly on
some level-- well, I don't want to pick and choose
favorites, but something in my brain-- I just really like
the B lymphocytes. So the B lymphocytes participate
in what's called the humoral response. And I'll tell you what humoral
means in a second. You'll see that T lymphocytes
participate in what's called the cell mediated response and
we're going to do that in a future video. They actually do certain classes
of T lymphocytes. We'll see that there are helper
T cells and there are cytotoxic T cells. I know it's all very confusing
the first time you see it, but that's why I just want
to focus on just this part right here. We're going to see in the future
that the helper T cells play a role in amplifying
and really activating this humoral response. But a simple way to think about
the difference between the humoral response and the
cell mediated response is, when I get infected--
let's say I get infected by a virus, right? At first, when a virus comes
into my system, it's just floating around in the
fluids in my system. The fluids of our system--
that's really what humoral responds to, into the humoral
fluids of your body. So you have your viruses. These are little viruses
floating around. So while they're floating around
and they're not sitting inside of cells, that's where
the humoral response can come into play. Same thing if we have little
bacteria floating around and they haven't infiltrated
cells yet. They're just floating around in
the fluid, then the humoral response can be useful
for that. Now if all of a sudden, these
guys have infiltrated cells-- so if the cells are now infected
with the virus and they're producing the viruses
using the mechanisms of the cell to produce more, then all
of a sudden we have to be a little bit more sophisticated
in how we deal with these cells and how we deal with the
viruses because they're not just going to be floating
around anymore. We probably want to just kill
this cell even though it was one of our own, but now it's
helping to make viruses. Or maybe it's been colonized
by bacteria. So in either case, you
want to kill this. And we'll talk more about that
in the cell mediating.