What is Primary Immunodeficiency?

April was Primary Immunodeficiency Awareness Month, but I was so overwhelmed with crazy end-of-semester stuff and crazy body stuff that I totally goofed—I didn’t write a single PI awareness post on my blog about PIBut better late than never right? So let’s talk about it. What is a primary immunodeficiency and what is it not?

What PI is:

  • A hereditary/genetic defect in the immune system.
  • A defect occurring in one or more components of the immune system.
  • A blanket term to describe more than 350 rare, chronic disorders in which part of the immune system is missing or functioning improperly.
  • Lifelong.
  • Treatable, but not curable.


Basically a primary immunodeficiency is a problem with your immune system that you’re born with (although they can develop later in life and often aren’t diagnosed for many years either way).


What PI is not:

  • Contagious.
  • An autoimmune disorder.
  • Just a “bad” immune system.
  • Visible.
  • A defect in the immune system caused by something else—like AIDS or chemotherapy (it’s not “acquired”).

So when someone tells you they have PI don’t get all weird about it. They’re not contagious. Most likely, they’re not dying. Just be cool.


What having PI means:

  • Increased susceptibility to contagious illnesses.
  • Increased susceptibility to infection.
  • Infections that are recurring, chronic, difficult to clear up, severe, or caused by unusual organisms.
  • You don’t build immunity from a previous infection (whether viral or bacterial).
  • You’re a medical zebra—PI is rare, so it’s a “zebra” condition instead of a more common “horse” condition.

Let me explain—no there’s too much. Let me sum up. Having a primary immunodeficiency means you get sick a lot, because your immune system doesn’t work like it should. Since it’s a genetic/hereditary disorder, having PI usually means it either runs in your family, or you’re really lucky and your genes mutated…

To better understand PI it’s important to understand how the immune system is supposed to work

How it Works – The Immune System

There’s two basic parts to the immune system: the innate immune system and the adaptive immune system.


The Innate immune system starts, like all of the cells that make up the immune system, in the bone marrow with a stem cell.  The several types of cells that make up the innate immune response (neutrophils, monocytes, natural killer (NK) cells, complement proteins) are ready to go straight to work once formed. They require no additional training to do their jobs.

In most cases of PI the innate immune response is a-okay. The problem occurs in the adaptive immune response.


The Adaptive immune system also starts in the bone marrow. There they become either  B-cells or T-cells, the two major parts of the adaptive immune sytem. Then they are split up. T-cells go to the Thymus to finish developing and get trained for their jobs as Killer T-cells, Helper T-cells, or Regulatory T-cells—which all basically deal with the body’s adaptive response to foreign substances (ie viruses) and make sure they don’t attack the body’s own tissues (as in autoimmune conditions).

B-cells stay behind and get edumacated in the bone marrow. They mature into Plasma cells, which in turn can mature further into Memory B-cells. Plasma cells are responsible for producing antibodies, which are highly specialized proteins that fit “invaders” like a key in a lock. Memory B-cells remember the invaders that you’ve encountered before so a rapid response can be mounted if you encounter it again.

In a lot of primary immunodeficiencies the main problem is with the B-cells. They don’t mature like they’re supposed to. They don’t pay attention in bone marrow class or just skip it all together. So they don’t make antibodies like they should and they definitely don’t remember past infections. It’s like your adaptive immune army is made up of a bunch of cats—they just do whatever the heck they want, which is usually nothing. So bacteria and viruses waltz in again and again, and even if they’ve gotten in before your cells are perpetually unprepared.

Basically your B-cells look like this:



So you can see why they might not be super effective…




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