Immunoglobulin (Ig) therapy is a medical treatment that delivers concentrated antibodies from donated human plasma into your body. These antibodies, primarily a type called IgG, are pooled from anywhere between 1,000 and 100,000 healthy blood plasma donors per batch. The treatment either replaces antibodies your body can’t make on its own or, at higher doses, calms an overactive immune system that’s attacking your own tissues.
What Immunoglobulin Therapy Is Made Of
IgG makes up more than 90% of the proteins in an Ig therapy preparation, and it’s the component responsible for the treatment’s effects. IgG is the most abundant antibody in your bloodstream. It recognizes and helps neutralize bacteria, viruses, and other threats. The remaining portion contains small amounts of other antibody types, signaling molecules, and proteins that mirror what’s naturally found in healthy blood plasma.
Manufacturing the product starts with a process developed in the 1940s called cold ethanol fractionation. Plasma is cooled and mixed with increasing concentrations of alcohol, which causes different proteins to separate out in stages. The fraction rich in IgG is then further purified using techniques like ion-exchange chromatography, which filters out contaminants, unwanted enzymes, and protein clumps. The end result is a highly concentrated, purified antibody solution ready for infusion.
How It Works in the Body
Ig therapy serves two fundamentally different purposes depending on the condition being treated, and the dose reflects that difference.
For people with immune deficiencies, the therapy acts as straightforward replacement. If your body produces too few antibodies to fight infections, regular Ig infusions supply what’s missing. This keeps your antibody levels high enough to prevent recurring bacterial and viral infections. The doses used for replacement are lower, typically given on a recurring schedule to maintain steady protection.
For autoimmune and inflammatory conditions, the therapy works differently. At much higher doses, the concentrated antibodies interact with your immune system in ways that dial down harmful inflammation. The pooled antibodies can block the receptors that immune cells use to attack your own tissues, neutralize inflammatory signals, and interfere with the process that targets healthy cells for destruction. In this role, Ig therapy is acting as an immune system regulator rather than a simple supplement.
Conditions Treated With Ig Therapy
The most established use is in primary immunodeficiency diseases, a group of inherited conditions where the body fails to produce adequate antibodies. Without treatment, people with these conditions face constant, sometimes life-threatening infections. Regular Ig therapy dramatically reduces that infection burden.
On the autoimmune side, one of the best-studied applications is chronic inflammatory demyelinating polyneuropathy (CIDP), a condition where the immune system damages the protective coating around peripheral nerves. In a major clinical trial of 117 patients, 54% improved with Ig therapy compared to just 21% on placebo. A Japanese study found an even higher response rate of 78% at 28 weeks of ongoing treatment, with only about 10% of responders relapsing over the following year. Patients typically see improvements in disability scores, grip strength, and overall muscle function.
Ig therapy is also used for Guillain-Barré syndrome (a rapid-onset nerve condition), certain blood disorders where the immune system destroys platelets, and Kawasaki disease in children. It has a growing list of off-label uses in other autoimmune and inflammatory conditions as well.
Intravenous vs. Subcutaneous Infusion
There are two ways to receive Ig therapy, and the choice affects your schedule, how you feel during treatment, and where you get it done.
Intravenous immunoglobulin (IVIG) is infused directly into a vein, typically every three to four weeks in a clinical setting. Each session can take several hours. Because a large dose enters the bloodstream at once, antibody levels spike right after infusion and then gradually decline until the next session. That swing between peak and trough can be significant, roughly a 900 mg/dL difference between the highest and lowest points.
Subcutaneous immunoglobulin (SCIG) is injected under the skin, usually weekly, and many patients learn to do it at home. Because the dose is smaller and more frequent, antibody levels stay much more stable, with only about a 100 mg/dL difference between peaks and troughs. SCIG also tends to cause fewer body-wide side effects like headaches and fatigue, though it’s more likely to cause temporary redness or swelling at the injection site. The two methods are considered therapeutically equivalent for primary immunodeficiency, so the choice often comes down to lifestyle preference and how well you tolerate each approach.
Common Side Effects
Most side effects are mild and temporary. The most frequent reactions feel like a mild flu: flushing, headache, nausea, fatigue, fever, chills, and general achiness. These typically resolve on their own within hours of the infusion ending, and they’re more common with intravenous delivery than subcutaneous.
Serious reactions are uncommon but worth knowing about. Blood clots occur in an estimated 1% to 17% of patients, a wide range that depends on individual risk factors like age, immobility, and pre-existing cardiovascular conditions. Kidney problems are rare but can be dangerous, particularly with certain formulations. Aseptic meningitis (a temporary inflammation of the membranes surrounding the brain) and hemolytic anemia (where the infused antibodies trigger breakdown of red blood cells) are other uncommon complications. Transfusion-related acute lung injury is the most dangerous reaction, causing sudden respiratory distress within six hours, but it’s extremely rare. Overall, fewer than 1% of patients experience delayed serious adverse effects.
IgA Deficiency and Anaphylaxis Risk
One specific safety concern involves people who have very low levels of a different antibody type called IgA. About 25% to 30% of people with IgA deficiency develop antibodies against IgA itself. When these individuals receive Ig therapy that contains even trace amounts of IgA, their immune system can react against it, sometimes severely. Up to 40% of people with selective IgA deficiency may carry these anti-IgA antibodies.
For these patients, subcutaneous delivery appears to be a safer alternative. In documented cases, patients who experienced full anaphylaxis during intravenous infusions were later able to tolerate subcutaneous Ig therapy without adverse effects for years. If you know you have IgA deficiency, this is something your treatment team will screen for and plan around before starting therapy.
What to Expect as a Patient
If you’re starting Ig therapy for an immune deficiency, expect it to be a long-term commitment. Your body doesn’t store the infused antibodies permanently, so regular infusions are needed to maintain protective levels. For autoimmune conditions, some people receive a course of treatment and then reassess, while others need ongoing maintenance.
The first infusion is typically given slowly to watch for reactions, with the rate gradually increased over subsequent sessions if everything goes well. Staying well-hydrated before and after infusions can reduce the likelihood of headaches and other side effects. Many patients on IVIG eventually develop a routine that allows them to work or read during their sessions, and those on SCIG often integrate home infusions into their weekly schedule with minimal disruption.