🎯 Lymphatic System Lesson

IgGAMED: how B cells make antibodies

B cells and the antibodies they produce are the other half of adaptive immunity, working alongside T cells but through a completely different mechanism.

IgG

80%, placenta

IgA

Secretory

IgM

First

IgE

Allergy

IgD

B activ.

📖 Full Breakdown

From B cell to antibody, and the five distinct classes produced

B cells recognize antigens, get activated by Helper T cells, and differentiate into plasma cells that manufacture antibodies.

IgG

The most abundant, 80% of antibodies

The only antibody class that crosses the placenta, providing passive immunity to a newborn. Dominant in the secondary (repeat exposure) immune response.

IgA

The secretory antibody

Found in saliva, tears, breast milk, and mucus — specifically guarding mucosal surfaces where pathogens frequently attempt to enter the body.

IgM

First responder, largest antibody

The first antibody produced during a primary immune response, and the most effective at activating the complement system.

IgE

The allergy and parasite antibody

Binds to mast cells, triggering histamine release — responsible for both allergic reactions and defense against parasitic infections.

IgD

B cell activation

Functions primarily as a B cell surface receptor involved in activation — the least well-understood of the five classes.

🩺 Clinical / Exam Application

A pregnant woman's IgG antibodies cross the placenta, giving her newborn temporary protection against diseases the mother has been exposed to or vaccinated against. Because IgG is specifically the ONLY antibody class capable of crossing the placenta, this passive immunity depends entirely on this one antibody type — IgA, IgM, IgE, and IgD do not provide this same protection, which is why newborns remain vulnerable to certain infections despite having some maternal antibody protection.

⚠️ Exam Alert

A frequently tested clinical fact: IgM is the antibody produced FIRST during a primary immune response, making an elevated IgM level (rather than IgG) a useful indicator of a recent, acute infection rather than a past one.

🚧 Common Trap

Don't assume all five antibody classes serve interchangeable, general-purpose roles. Each has a distinct, specific job — confusing IgE (allergies/parasites) with IgA (mucosal secretions), for example, would lead to completely wrong conclusions about a patient's presentation.

✅ Quick Check

A newborn has some immunity to diseases their mother was vaccinated against, despite having no vaccinations themselves. Which antibody class explains this, and why is it the only one capable of it?

📝 Exam Prep

Common Exam Questions

❓ What are the five antibody (immunoglobulin) classes?

✅ IgG, IgA, IgM, IgE, and IgD. IgG is most abundant and crosses the placenta; IgA is secretory (mucosal surfaces); IgM is produced first in a primary response; IgE is involved in allergies and parasite defense; IgD functions in B cell activation.

❓ Why is IgG significant during pregnancy?

✅ IgG is the only antibody class that crosses the placenta, providing the newborn with passive immunity against diseases the mother has been exposed to or vaccinated against.