In today’s blog, we are going to take a look at part 2 of Innate vs. Adaptive immunity. We will talk about Adaptive Immunity. If you happen to miss the first blog, click this link to read more on innate immunity. 

In part one, I introduced two forms of immunity: innate, and adaptive. I explained to you how innate immunity works. In order for the adaptive immune system to kick in, the innate immune system needs to work first.

Today’s blog is all about adaptive immunity, also known as acquired immunity.

What Is Adaptive Immunity?

• Also known as acquired or programmed immunity.
• This immunity is specific because the response that happens is aimed at a particular non-self antigen.

Adaptive immune cells undergo basic training to recognize the difference between self and non-self proteins. 

1. Self-tolerance – the ability of the cells to learn to recognize the self-antigens and avoid attacking them.
2. Autoimmune disease – is caused by a loss of self-tolerance. 

NOTE: The purpose of this basic training is that the cells only recognize the non-self proteins and mount an immune response against those foreign invaders. 

Lymphocytes – B cells and T cells.

Major Histocompatibility Complex (MHC)

• their task is to self-bind and non-self antigens and then to

display those antigens on the cell surface.

Two Types of MHC

1. Class 1 or MHC I

 – they are found on the surface of all body cells except red blood cells because they do not have a nucleus. 

– displays antigen that is internally produced-endogenous antigens. 

 NOTE: In a healthy cell the MHC-1 will have normal body proteins inside of it

2. Class II or MHC II 

• can be only found on immune cells capable of phagocytosis.
  • can display both MHC I and MHC II.
  • When cells are capable of phagocytosis (cell-eating), the proteins they bring in are exogenous (from the outside cell). 
• also known as Antigen Presenting Cells (APC).

Cell-mediated immunity – The communication between the T and B cells is a dynamic one, not a compartmentalized one. Cell mediated immunity works together with humoral immunity to fight different diseases that infects us. It is also responsible for fighting cancerous cells when they are fighting normal skin cells within our body. 

Antibody-mediated immunity – B cells recognize antigens, and it becomes activated into plasma cells and makes antibodies. An antibody mediated immune response is the basis for most vaccination responses. This involves the human body producing antibodies to then fight off potential invaders in the future, from previous infections.

What About MHC II?

• is responsible for activating t helper cells if an antigen-presenting cell displays a pathogen that it has internalized.

• APC with MHC II or antigen complex can activate a T helper cell with the appropriate receptor. 
• Activated T helper cells – memory helper T cells and activated helper T cells.

NOTE: Only APC can display MHC II. 

Now, we are going to distinguish the differences between Innate and Adaptive Immunity. Also, we’ll talk about their similarities as well. Refer to the chart below.

Innate Immunity	Adaptive Immunity	Similarities
Non-specificRapid ResponseMast CellsNeutrophilsMonocytes	SpecificSlow first responseMemory cells B cells and T cellsCytotoxic and helper T cells	Dendritic cellsMacrophagesNK cells

Innate immunity only functions during the intervals between exposure. Our adaptive immunity, on the other hand, is always functional, continuously producing antibodies to help keep us protected from diseases on an ongoing basis. Whereas innate immunity provides the “first line of defense” against roundworms, adaptive immunity builds on this and helps to keep those worms out of our system for good.

It is important to know that what we are calling “adaptive immunity” is a more complicated system than “innate immunity”.

Innate and adaptive immunity are both extremely important to our immune systems. Knowing more about them will help you understand how they work together to protect us from infection.

Below, you will find my video on this topic! Hope this helps you learn more about how the innate and adaptive immune systems are different.