Immune System Cell Types: Core Functions & White Blood Cells Guide

If we are going to learn about the immune system,  the best way to start is by introducing the major   cell types that make up the immune system and  their basic functions. Each of these types will   be examined in more depth in their own separate  tutorials later in the series, but it’s a good  

idea to do a quick survey up top, so that we can  get a sense of all the components, and then expand   on each one later. Now, unlike other systems in  your body, such as the digestive system or the   circulatory system, which are made up of distinct  organs that are fixed in place, the immune system  

is made up of billions of individual white blood  cells that are mobile throughout your body.   These circulate through your bloodstream  and move around in your tissues, patrolling   for signs of infection or tissue damage. When  they do detect a threat, they communicate with  

other immune cells so as to quickly mobilize a  counterattack. As much as we may be tempted to   bestow these cells with sentience, as though  they are literal bodyguards, in actuality they   are simply responding to specific chemical  stimuli. But we are talking about a dynamic,  

complex system, involving billions of different  cells constantly moving and interacting with   one another, so let’s first boil down the  roles of immune cells to four main functions.  Function one, recognize. An immune cell needs  to be able to recognize when there is a threat.  

This involves being able to distinguish  between self and non-self, meaning that   it must differentiate between a cell of the  human body and an infectious bacterium or virus.   It also needs to recognize when self cells  become cancerous and need to be destroyed,  

or when there has been damage to self tissue that  needs to be healed, such as when you get a cut.   An immune cell can also receive chemical  messages from other cells that can influence   its activity. These messages are often in  the form of proteins that are secreted,  

such as cytokines, which influence how an  immune cell responds to a particular threat,   or chemokines, which help guide immune  cells to the site of damage or infection.  Funcion two, react. Once they recognize a  problem, immune cells react by deploying  

effector functions, which are specific  to the type of threat at hand. These   effector functions can include mechanisms  which kill pathogens or infected cells,   stimulation of wound healing,  clearance of cellular debris,  

and coordination of the immune response  through cytokine and chemokine signals.  Function three, regulate. Although immune cells  are very good at killing infectious organisms,   they can also cause damage to self tissue,  so immune cells need to be able to regulate  

themselves and each other to prevent an  immune reaction from getting out of control.   Before they are able to carry out their effector  functions, immune cells need to be “activated.”   Immune cell activation can happen by receiving  multiple signals indicating the presence of  

a pathogen, or by receiving a specific set  of signals called “co-stimulatory signals”   from other immune cells. The requirement for  activation and co-stimulation works like a   system of checks and balances, ensuring that  immune cells don’t accidentally become activated  

and cause unnecessary damage to host tissue.  We’ll talk about this process in considerable   depth later in the series. Additionally, many  types of immune cells send cytokine signals   to tell other cells to ramp down the immune  response and begin repairing damaged tissue. 

And finally, function four, remember.  Immune cells called T and B lymphocytes   have the ability to remember specific threats.  Emerging research suggests that other immune cells   may also be able to remember previous  infections. This concept of immune memory  

is the basis behind vaccinations, and it will  be discussed extensively later in the series.  Now, the manner in which immune cells carry out  these four functions of recognizing, reacting,   regulating and remembering is largely dependent  on where in the body the cells are located,  

and later we will learn about precisely  how immune cells are spatially distributed   throughout lymphoid tissue, as well as  the ways in which the lymphatic system   helps control these properties. However, there  are also lots of unique cell types with distinct  

identities and effector functions  that help determine what a cell does   during an immune response, so let’s  move forward and talk about these next.