Introduction

In fact, there are some parts omitted in Allergy Encyclopedia. In Allergy Encyclopedia, we introduced that macrophages and dendritic cells present antigen to Th1 when pathogens and the like invade, and present antigen to Th2 when allergens and the like invade.

Naive T cell

To be precise, the cell where they present the antigen is a cell like “pupa” common to Th1 and Th2 even if the invasion is pathogens or allergens. This “pupa” cell is called “Naive T cell”.

Differentiation

Then, after presenting antigen, macrophages and dendritic cells make Naive T cells Th1 or Th2. Th1 and Th2 are relations like close relatives. In this way, specialization of cell function is called “differentiation”.

The differentiation process in detail

Let’s look at the differentiation process more particularly.
Macrophages and dendritic cells tell Naive T cells which to differentiate by sending fixed substances.
When Naive T cells are required to differentiate into Th1 due to invasion by pathogens and the like, macrophages and dendritic cells send substances such as “IL12”* and “IFN-γ”. Then proteins such as “STAT1” and “STAT4” inside Naive T cells react to them, and turn ON the switch named “T-bet”. T-bet transform Naive T cells into Th1.
On the other hand, when Naive T cells are required to differentiate into Th2 due to invasion by allergens and the like, macrophages and dendritic cells send substances called “IL4”*. Then proteins called “STAT6” inside Naive T cells react to them, and turn ON the switch named “GATA3”. GATA3 transform Naive T cells into Th2.
Depending on the type of substance sent, the switch that turn ON changes, and then differentiation is done.
* IL means interleukin.