Type III hypersensitivity


00:00 / 00:00



Type III hypersensitivity

Immune system

General infections


Neonatal sepsis


Hypersensitivity reactions

Type I hypersensitivity

Food allergy



Type II hypersensitivity

Immune thrombocytopenic purpura

Autoimmune hemolytic anemia

Hemolytic disease of the newborn

Goodpasture syndrome

Rheumatic heart disease

Myasthenia gravis

Graves disease

Pemphigus vulgaris

Type III hypersensitivity

Serum sickness

Systemic lupus erythematosus

Poststreptococcal glomerulonephritis

Type IV hypersensitivity

Graft-versus-host disease

Contact dermatitis


Transplant rejection

Graft-versus-host disease

Cytomegalovirus infection after transplant (NORD)

Post-transplant lymphoproliferative disorders (NORD)


X-linked agammaglobulinemia

Selective immunoglobulin A deficiency

Common variable immunodeficiency

IgG subclass deficiency

Hyperimmunoglobulin E syndrome

Isolated primary immunoglobulin M deficiency

Thymic aplasia

DiGeorge syndrome

Severe combined immunodeficiency

Adenosine deaminase deficiency


Hyper IgM syndrome

Wiskott-Aldrich syndrome

Leukocyte adhesion deficiency

Chediak-Higashi syndrome

Chronic granulomatous disease

Complement deficiency

Hereditary angioedema


Immune system organ disorders


Ruptured spleen

Immune system pathology review

Blood transfusion reactions and transplant rejection: Pathology review

Immunodeficiencies: T-cell and B-cell disorders: Pathology review

Immunodeficiencies: Combined T-cell and B-cell disorders: Pathology review

Immunodeficiencies: Phagocyte and complement dysfunction: Pathology review


Type III hypersensitivity


0 / 8 complete

USMLE® Step 1 questions

0 / 2 complete

High Yield Notes

2 pages


Type III hypersensitivity

of complete


USMLE® Step 1 style questions USMLE

of complete

A 35-year-old man is evaluated for a 6-hour history of fever, itchy rash, and generalized body aches. Ten days ago, he received a snake bite treatment in the emergency department. Physical examination is significant for fever, an urticarial rash, myalgia, and polyarthritis. Urine dipsticks show 2+ protein. Serum complement levels are reduced. Which is the most likely cause of this patient’s condition?  

Memory Anchors and Partner Content

External References

First Aid








IgG antibodies p. 103

in type III hypersensitivity reactions p. 111

Type III hypersensitivity p. 111

C3 deficiency and p. 105

organ transplants p. 117

External Links


Content Reviewers

Rishi Desai, MD, MPH


Tanner Marshall, MS

Having a hypersensitivity means that someone’s immune system has reacted to something in a way that ends up damaging them, as opposed to protecting them.

There are four different hypersensitivities and the third type or type III hypersensitivity reaction happens when antigen-antibody complexes deposit in blood vessel walls, causing inflammation and tissue damage.

Alright so first off, type III hypersensitivity reactions are mediated by immune complexes. Immune complexes, aka antigen-antibody complexes are made of two parts—the antigen and the antibody.

Antibodies, sometimes called immunoglobulins, are produced by plasma cells, which are basically fully matured and differentiated B cells.

Initially these cells make IgM - which can be secreted or bound to the plasma cell surface where it acts as a B cell receptor.

When a B cell undergoes cross-linking of two surface bound IgMs, it then takes up the antigen and presents a piece of it to T helper cells via t cell receptor to the MHC- class II molecule presenting the piece of antigen, along with costimulatory molecule CD4.

The B cell’s CD40 also binds to the T cell’s CD40 ligand, and then the t cell releases cytokines, which results in b cell activation and class switching, or isotype switching, where it changes the type of antibodies it makes.

In type III hypersensitivity reactions, typically B cells will switch from making IgM to making IgG antibodies.

Now remember that all antibodies are specific, right? Meaning that they recognize specific molecules called antigens, the second part of immune complexes.


Type III hypersensitivity is a type of immune response in which antigen-antibody complexes accumulate in the tissues and cause inflammation and tissue damage. This type of hypersensitivity is also known as immune-complex-mediated hypersensitivity. Examples of Type III hypersensitivity reactions include systemic lupus erythematosus, rheumatoid arthritis, and serum sickness. Symptoms can vary depending on the tissues affected and may include joint pain and swelling, rashes, fever, and kidney damage. Treatment options may include removing the triggers, and medications like antihistamines, nonsteroidal anti-inflammatory drugs, and corticosteroids.


Copyright © 2023 Elsevier, except certain content provided by third parties

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.