Human Physiology - Innate Immune System

>>Dr. Ketchum: So we are going to go ahead and continue our discussion of the immune

system, and we’ll be discussing innate immunity. Now before we discuss innate immunity, you

need to understand that there’s actually two different types of immunity—one of those

being innate immunity, which is also called nonspecific immunity, and the other is called

acquired or adaptive immunity, which is also known as specific immunity. But just to give

you a quick overview of both of these, when you first think about the nonspecific or the

innate immunity, it’s a very rapid response. This is your first line of defense. And what

this does is it gives your body time for the specific immunity to kick in. So innate immunity

is always there. It’s present; it’s going to happen as soon as your body is invaded

by a foreign object, and then the specific immunity will take over after that. It’s

rapid, and it’s also not selective. So it’s not targeting specific species of invaders,

for example. It’s not specific. It just wants to kill foreign invaders, and that’s

the end of it. The innate immunity involves physical and chemical barriers, and it also

includes cellular defenses. Now once the innate immunity has occurred, then the next type

of immunity that will occur or kick in is the acquired immunity. It’s a slow response.

And so because it’s a slow response, it’s very selective in what it’s killing. It

may kill a specific bacterial cell or a specific virus, and specific immunity includes two

different types of responses—humoral responses, which are also called antibody-mediated responses,

and cell-mediated responses, which are also called cytotoxic lymphocytes. Here’s our

analogy. When you think about an innate response, the castle is the body. And the first thing

that this innate response wants to do is it wants to prevent that invader from entering

the body. And once that invader invades the body, then the innate response will have some

other methods for killing the invaders as well. These things are all taking place as

the acquired response is just getting started—but remember it’s slow, so it takes a while

to get the acquired response going.

So neutrophils, the eosinophils, basophils and monocytes are all cells that are important

in an innate response. The lymphocytes, on the other hand, are the type of white blood

cell that are important in the acquired response. You don’t have to memorize the amount of

each of these cells in a microliter or their diameters or any of that. You need to understand

their anatomical features and their functions. So these are important columns here, but you

do also have to know their abundance—their relative abundance. So again, if you remember

“Never Let Monkeys Eat Bananas,” that tells you the most abundant leukocyte all

the way to the least abundant leukocyte, which are your “bananas” or your basophils,

so that way you don’t have to memorize the amount per microliter. The reason this is

important is because if you’re looking at a slide—let’s say you take a blood smear

on a microscope slide—and, and this is a healthy person, and you’re going through

and you’re identifying all the various white blood cells. Well if you’re finding more

basophils than you are neutrophils, then you’re probably not correctly identifying those cells.

Okay, so here’s a flow chart that I put together to help organize the innate versus