A Beginner's Guide to How the Immune System Turns on the Body

If you've spent any time around Prolato's work, you've seen the list: rheumatoid arthritis, lupus, Graves' disease, myasthenia gravis, Sjögren's syndrome, systemic sclerosis, myositis. Different names, different organs affected, wildly different symptoms — but they all share one root cause. They're autoimmune diseases, which means the same basic malfunction is happening under the hood in every single one.

Before we dive into each condition individually this quarter, it's worth stepping back and asking the more fundamental question: what does "autoimmune" actually mean, and why does the body do this to itself?

Your Immune System's Actual Job

Think of your immune system as a security team patrolling your body around the clock. Its job is to tell the difference between "self" (your own cells and tissues) and "non-self" (viruses, bacteria, and other invaders), and to eliminate the non-self threats before they cause harm.

To do this, immune cells rely on markers — a kind of ID badge — present on the surface of cells. Under normal circumstances, the immune system recognizes its own badges, leaves those cells alone, and reserves its attacks for anything that doesn't have the right credentials.

Where It Goes Wrong

In an autoimmune disease, that recognition system breaks down. The immune system starts treating some of the body's own healthy tissue as if it were foreign, and mounts a full attack against it — inflammation, tissue damage, and in some cases, permanent organ damage. As the American College of Rheumatology puts it, in autoimmune disease the immune system essentially recognizes itself as foreign and inappropriately activates, sending immune cells to attack the body's own parts.

Which tissue gets targeted determines which disease develops:

• In rheumatoid arthritis, the attack centers on the joints.
• In lupus, autoimmune antibodies can attach to tissue throughout the body — joints, skin, kidneys, and more.
• In Graves' disease, the target is the thyroid gland, causing it to overproduce hormone.
• In myasthenia gravis, the immune system interferes with communication between nerves and muscles.
• In Sjögren's syndrome, the moisture-producing glands (tear and salivary glands) are the primary target.
• In systemic sclerosis and myositis, connective tissue and muscle bear the brunt of the attack.

Different targets, same underlying mistake.

Why Does This Happen?

This is the question researchers are still working to fully answer, and the honest truth is that no single cause explains every case. What the research does point to is a combination of factors:

Genetics. Certain gene variants — particularly in a group called human leukocyte antigen (HLA) genes — are linked to higher risk for various autoimmune diseases. But genetics alone isn't the whole story: studies of identical twins show that when one twin develops an autoimmune disease, the other doesn't always develop it too, even though they share the same DNA. That gap is where environmental factors come in.

Infections. Sometimes the immune system's response to a real infection seems to spill over onto healthy tissue. Researchers believe this may explain why rheumatoid arthritis develops in some people, and why psoriasis sometimes follows a bout of strep throat — the immune system, already activated to fight the infection, ends up catching healthy cells in the crossfire.

Environmental exposures. Pollution, certain chemicals, diet, and other lifestyle factors have all been studied as potential contributors to autoimmune disease risk, on top of a person's genetic background.

The hygiene hypothesis. One widely discussed theory suggests that reduced exposure to microbes in early life — a byproduct of modern sanitation — may leave the immune system's regulatory circuits under-trained, making it more prone to misfiring against the body's own tissue later on. It's a compelling idea, but researchers are clear that it's one piece of a larger, multi-factorial puzzle, not a complete explanation on its own.

Physical stress or injury. In a smaller number of cases, repeated physical stress on a particular part of the body — like the constant strain on a runner's heel — may expose tissue that isn't normally in contact with immune cells, triggering an inflammatory response in that area.

How Common Is This, Really?

More than 80 to 100 distinct autoimmune diseases have been identified, and together they affect a significant share of the population — some estimates put the global figure at around 10%. In the U.S. alone, more than 24 million people live with one of these conditions. Despite how common autoimmune disease is as a category, individual conditions can still take years to diagnose, partly because symptoms often overlap with other illnesses and partly because there's no single test that screens for "autoimmunity" in general — each disease has to be worked up on its own.

Why This Matters for the Studies We Run

Every condition Prolato studies this quarter — RA, lupus, Graves', MG, Sjögren's, systemic sclerosis, myositis — sits under this same autoimmune umbrella. Understanding the shared mechanism doesn't just make each individual deep-dive easier to follow; it also explains why research across these conditions often cross-pollinates. A treatment approach that helps restore immune tolerance in one autoimmune disease frequently opens doors for researchers studying another.

Over the coming weeks, we'll take this same lens to each condition individually — what makes it unique, what current research is exploring, and what it means for the patients living with it.

Sources

1. Johns Hopkins Medicine — Autoimmune Disease: Why Is My Immune System Attacking Itself?
2. American College of Rheumatology — Autoimmunity and Triggers
3. MedlinePlus (National Library of Medicine) — Autoimmune Diseases
4. Cleveland Clinic — Autoimmune Diseases: Types, Symptoms & Treatments
5. National Institute of Environmental Health Sciences (NIEHS) — Autoimmune Diseases
6. WebMD — Autoimmune Diseases: Causes, Symptoms, and Treatments
7. Bach, J.F. — The hygiene hypothesis in autoimmunity: the role of pathogens and commensals, Nature Reviews Immunology
8. PMC/NCBI — A Potential Link between Environmental Triggers and Autoimmunity
9. PMC/NCBI — Autoimmune Diseases: Molecular Pathogenesis and Therapeutic Targets

Note: statistics and mechanisms above are paraphrased and synthesized from the sources listed. Recommend a quick compliance/IRB pass before publishing, per Prolato's usual review process for condition-related content.