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Mechanism of Immunity and the Working of Immune Cells / Let's take a look at how the immune system works to protect the body from infections.

Innate Immunity and
Acquired Immunity

Why is it that we don't catch colds every day, and why are we less susceptible to illnesses that we've had before?
That's thanks to the immune system.
There are two major phases of the immune system.
"Innate immunity" is the first to fight pathogens that enter the body, and any of the pathogens that pass through the
innate-immunity defenses are then fought by "acquired immunity".

Innate immunity - Attacks enemies from the outside as soon as they are found / Acquired immunity - Remembers enemies that have entered before, and attacks them effectively from the second time onward
  • macrophagesWhen enemies (foreign matter such as bacteria or viruses) enter the body, macrophages swallow them whole. Their name, which means "big eater", comes from this behavior. They also serve to convey information about enemies to other immune cells.
  • white blood cellsWhite blood cells mainly swallow and dispose of bacteria. After killing the bacteria, the white blood cells themselves die and become pus.
  • NK cellsWhen NK cells find cancer cells or virus-infected cells, they attack them on their own.
  • helper T cellsWhen they receive notification from dendritic cells, macrophages, etc. that there is an enemy invasion, they convey the notification to Killer T cells and B cells.
  • Killer T cellsThey receive commands from dendritic cells, helper T cells, etc. to kill cells that have been invaded by enemies from the outside.
  • B cellsThey receive commands from dendritic cells, helper T cells, etc. to produce antibodies to fight off bacteria and viruses.
    Some B cells can memorize the characteristics of antigens.
  • Dendritic cells"Dendritic cells" which belong to innate immunity convey information about antigens ("enemies") to other immune cells, and serve as a bridge between innate immunity and acquired immunity.

What are pDCs?

Dendritic cells are divided into two major groups,
and the ones that are especially active when a virus invades are pDCs (plasmacytoid dendritic cells).
pDCs are normally dormant cells, but they are activated when they encounter antigens ("enemies").
Activated pDCs act as "leaders" that give instructions to various immune cells in both the "innate immunity" and "acquired immunity" phases, thereby regulating immune functions.

Role of pDCs as "leaders" of the immune system

pDCs play an important role in defense from viral infection.

1.Virus decomposition / 2.Killing of infected cells by NK cells*3 / 3.Killing of infected cells by Killer T cells*2 / 4.Promotion of antibody production by B cells*3 / 5.Production of natural antibodies by B cells

Reference: modified from "Chemistry and Biology" 53(9): 626-632, 2015.

*1 J. Exp. Med. 147: 1314-1333, 1978
*2 Immunity 35, 958-971, 2011
*3 J. Exp. Med. 205, 1621-1634, 2008 Immunity 34, 247-257, 2011

Lactic acid bacteria that activate pDCs, the 'leaders' of the immune system! Learn about L. lactis Plasma!
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