As I told you before, 
the bone marrow has a stem cell
Those stem cells change to RBCs,  platelets, and WBCs
The WBCs have two types: 
non-granular and granular
The granular WBCs are: 
eosinophils, basophils, neutrophils
As I explained, eosinophils have red granules
basophils have blue granules 
and neutrophils have neutral granules
The non-granular WBCs are two types
first, lymphocytes, which we are going to discuss in details now
secondly monocytes
Monocytes can change into macrophage
We are going to discuss them later
Now, let's discuss lymphocytes
Lymphocytes are like high-school students
Some of them go to school of medicine
Others go to school of pharmacy
What does this mean?
When I enter medical school, I become a doctor
So I take its name accordingly
When I enter pharmacy school, I become a pharmacist
Pharmacy , pharmacist
Both start with the letter P
Let's imagine that school of medicine is a gland
above the thyroid gland
more like a curtain
This is the thymus
Thymus starts with T
so it's called T. Lymphocytes
Then the Bursa gland
found in birds
Bursa of Fabricius
But it's found in the human body in the lymphoid tissues of the intestine
Bursa starts with B 
so it's called B. Lymphocytes
So we have two very important cells in the lymphocytes
T. Lymphocytes which means thymus dependent
and bursa dependent 
or bone marrow dependent
The third cell is the natural killer
it kills the deviated or unwanted cells 
like cancer cells or viral-infected cells
or TB infected cells
The natural killer gets rid of any deviated or unwanted cells
So when I ask what is a natural killer cell
you say that it is a non-T and non-B
When I enter medical school, there are specializations
Same goes for T. Lymphocytes, they have specializations
there is T. lymphocytes helper
and T. lymphocytes suppressor 
its new name is "regulator" to regulate the immune system
The third type is T. lymphocytes cytotoxic
cyto means cell
toxic means it intoxicates the cell
which cell? 
the deviated cell
The bursa cells don't have many specializations
except for the B cell
So Lymphocytes have 3 types 
Thymus dependent T, Bursa dependent B
and non-thymus, non-bursa 
non-T, non-B (natural killer)
T. lymphocytes have 3 types
Helper, suppressor or regulatory 
 and cytotoxic that kills or intoxicates any deviated cell
Once I graduate from school of medicine, 
I can't have my own clinic or practice my job
as I still didn't have a training
I was just studying books now I need to practice
Where do I practice?
In hospitals
The first hospital is the lymphnodes
The second hospital is the spleen
So this is where I practice after graduation 
to have my own clinic or practice my profession
Likewise, the T. lymphocytes or B. lymphocytes pass through the first stage
which is the primary lymphoid organs
So when you are asked about the primary lymphoid organs
you say that they are the thymus or bursa (bone marrow)
The second stage is the secondary lymphoid organ
which are the lymphnodes and the spleen
They get out very active
or as we call it "immunological activation"
now they are able to work with the immune system
but those are independent,
they can't work
only when they get out of the secondary lymphoid organs,
they will start working and become actively immunological
So now we have primary lymphoid organs 
which are the thymus and bursa
they graduated and have to take a training 
so they move to the secondary lymphoid organs
like lymphnodes and spleen
There are many other secondary lymphoid organs
like MALT which is 
mucosa-associated lymphoid tissue
like tonsils
like appendix
All these are considered secondary lymphoid organs
but these two are the most important secondary lymphoid organs
Here is the bone marrow
it produces undifferentiated mesenchymal cells
we call it pluripotent hematopoietic or stem cell
This stem cell produced from the bone marrow 
has three types
WBCs , platelets and RBCs
The origin of the platelets is a cell called megakaryocyte
it's not important now
The important thing is that it produces RBCs, platelets and WBCs
WBCs are two types
Lymphocytes or lymphoyds
and myeloids
which are granular and non-granular
This is another way
Lymphocytes have two types
T cells and B cells
As we said before, T cells will go to the thymus 
B cells will go to the bursa
B cells change into plasma cells
and plasma cells produce anti-bodies
T cells are activated according to their types
T. helper, T. cytotoxic, T. regulator
Myeloids have eosinophils, basophils and neutrophils
Eosinophils have red granules
Basophils have blue granules
Neutrophils have colorless granules
and monocytes where it is non-granular
like lymphocytes
This can become a macrophage
some unknown tissues become mast cells
This is the first cell we are going to discuss 
which is the macrophage
this big red cell in the middle as you can see
These are originally phagocytic cells
but they are also antigen-presenting cells
The next one is neutrophils
it has granules as you can see 
but they are not very clear
but when you see the eosinophils, you will find them red as you can clearly see
basophils have blue granules
The mast cells ..
We are going to discuss them later on
These are the Natural Killer cells
As we said, macrophage are phagocytic cells
they eat
and at the same time are antigen-presenting cells
Neutophils are also phagocytic cells
Eosinophils kill parasites
they are present in cases that have allergy from parasites
Neutrophils are phagocytic cells and unknown and all of that
The Natural Killer can destroy any abnormal or altered cells
The antigen-presenting cells can be  dendritic cells, macrophages and B lymphocytes
as they all have receptors and protein number 7
This is the drawing of the dendritic cells
The second drawing is for macrophage
It also has receptors that make phagocytosis for the antigen and then recognize it
then represent it by the MHC
Then we have the B-lymphocytes
they take the antigen from the receptors called anti-body receptors
This is how they look under the microscope
