What kind of condition is Sweet’s syndrome?

Updated 14/02/17.

What kind of condition is Sweet’s syndrome?

Sweet’s syndrome is a rare autoinflammatory condition and form of neutrophilic dermatosis (Ahmadinejad et al, 2014:236; Ciccarelli et al, 2013; Marzona et al, 2014).

What are neutrophilic dermatoses?

Neutrophilic dermatoses are skin conditions that occur as a result of lots of white blood cells called neutrophils infiltrating the tissues. They can sometimes be a sign of underlying illness. Neutrophilic dermatoses include Sweet’s syndrome, neutrophilic dermatosis of the dorsal hands, Behcet’s syndrome, pyoderma gangrenosum, neutrophilic eccrine hidradenitis, erythema elevatum diutinum, and bowel-associated dermatitis-arthritis syndrome.

What are autoinflammatory conditions?

Autoinflammatory conditions are a fairly new category of rare diseases that cause inflammation, sometimes widespread inflammation in the body, normally for unknown reasons. They develop as a result of errors in the innate immune system, the body’s most primitive, ‘hard-wired’ immune system.

The term ‘autoinflammatory’ first appeared in the scientific ‘Cell’ journal in the spring of 1999 (Ciccarelli et al, 2013). Originally, autoinflammatory conditions only referred to hereditary recurrent fever syndromes, e.g. familiar mediterranean fever (FMF) and TNF receptor-associated periodic syndrome (TRAPS). At a later date, the definition of an autoinflammatory condition was extended to include other diseases.

What causes these errors in the innate immune system?

Most autoinflammatory conditions are genetic, and errors in the innate immune system occur as a result of gene mutation that affects how it works. However, there are some autoinflammatory conditions, including Sweet’s syndrome, where most of the time there is no clear genetic cause.

What causes Sweet’s syndrome if there is no clear genetic cause?

In autoinflammatory conditions where there is no clear genetic cause, people sometimes have certain genes that increase their risk of developing one of these conditions, but something may be needed to trigger it. However, autoinflammatory conditions are still poorly understood, and some people may or may not develop one of these conditions for reasons that we do not yet understand. For example:

  • Will develop an autoinflammatory condition even though certain genes are not present.
  • Will not develop an autoinflammatory condition even if they have a particular gene.
  • Will develop an autoinflammatory condition even if there is no known trigger.

My doctor said that Sweet’s syndrome is an autoimmune condition. Is this true?

No. Sweet’s syndrome is an autoinflammatory and not an autoimmune condition. However, it is often called an autoimmune condition because it seems to ‘behave’ like one, and until fairly recently, researchers and doctors did not know or were not certain what kind of condition Sweet’s syndrome might be. Also, most people, particularly those who are not health professionals, are not familiar with the term ‘autoinflammatory’. Therefore, they have a tendency to assume that it means the same thing as ‘autoimmune’.

Are autoimmune and autoinflammatory conditions similar?

Yes. Autoimmune and autoinflammatory conditions are similar, and both occur as a result of the immune system being overactive (not underactive and needing to be ‘boosted’. This is a common myth), and this then causes inflammation and sometimes tissue damage.

What is the main difference between an autoimmune and autoinflammatory condition?

The main difference between autoimmune and autoinflammatory conditions is that they involve different parts of the immune system. Autoimmune conditions involve the adaptive or acquired immune system, and autoinflammatory conditions involve the innate or non-specific immune system.

How does the adaptive immune system work? How do autoimmune conditions affect the body?

How does the adaptive immune system work?

When the body is attacked by a foreign invader such as a bacteria or virus, your immune system tries to defend it. One of the ways in which it does this, is by producing antibodies in response to antigens – mainly proteins or sugars on the surface of a cell or a non-living substance, that the adaptive immune system produces antibodies in response to. These antibodies, which are antigen or germ-specific, i.e. designed to fight off a specific type of antigen or germ, then target and destroy the foreign invader.

Unlike the innate immune system (see ‘How does the innate immune system work?’), the adaptive immune system develops as a person grows, so not only does it produce antibodies, but also ‘remembers’ foreign antigens. This means that it will recognize these antigens if they come back, and rapidly produce the right kind of antibodies, i.e. antigen or germ-specific antibodies, in response to them, often killing off an infection so quickly that it doesn’t have time to take hold.

How do autoimmune conditions affect the body?

In autoimmune conditions, the adaptive immune system doesn’t work properly, and immune cells mistake your body’s own natural proteins for foreign invaders and start to attack them. This process is known as autoimmunity, i.e. your immune system attacks your own body or ‘the self’ (‘auto-‘ meaning ‘self’). Antibodies known as autoantibodies are produced in response to the body’s own proteins, lock-on to the proteins to try and block and destroy them, and this causes inflammation and potential tissue damage.

How does the innate immune system work? How do autoinflammatory conditions affect the body?

How does the innate immune system work?

As well as an adaptive immune system, the body has a more primitive, inborn immune system called the innate immune system. It uses white blood cells or inflammatory cells called granulocytes and monocytes to defend the body and destroy harmful substances, but it does not ‘remember’ foreign invaders or antigens, and does not produce antibodies in response to them.

How do autoinflammatory conditions affect the body?

Unlike autoimmune conditions, in autoinflammatory conditions there is no production of autoantibodies in response to naturally occurring proteins in the body. In Sweet’s syndrome, cytokines can sometimes be produced in response to the presence of antigens, which eventually leads to the activation of neutrophils (a type of granulocyte), and this is known as hypersensitivity reaction. However, most of the time, these cells are produced and activated for no known reason at all. This then causes inflammation and potential tissue damage.

Key points.

  • Autoinflammatory conditions involve the innate immune system.

  • Autoimmune conditions involve the adaptive immune system.

  • In both conditions, the immune system is overactive and causes inflammation, but this happens for different reasons.

  • In autoimmune conditions, autoantibodies are produced in response to naturally occurring proteins in the body. This causes inflammation and potential tissue damage.

  • In autoinflammatory conditions, antibodies are not produced. Inflammatory cells are simply activated, often for no known reason. This causes inflammation and potential tissue damage.

References.

Ahmadinejad, Z., Mansouri, S., Ziaee, V., Aghighi, Y., Moradinejad, M. and Fereshteh-Mehregan, F. (2014) Periodic Fever: A Review on Clinical, Management and Guideline for Iranian Patients – Part II. Iranian Journal of Pediatrics, Jun;24(3):229-40 (online).

Ciccarelli, F., De Martinis, M. and Ginaldi (2013) An update on autoinflammatory diseases. Current Medicinal Chemistry,  Jan; 21(3): 261–269 (online).

Marzano, A., Fanoni, D., Antiga, E., Quaglino, P., Caproni, M., Crosti, C., Meroni, P. and Cugno, M. (2014) Expression of cytokines, chemokines and other effector molecules in two prototypic autoinflammatory skin diseases, pyoderma gangrenosum and sweet’s syndrome. Clinical and Experimental Immunology, Jun 5 (online).

Further information.

Autoinflammatory Alliance (2015) Autoinflammatory Disease Comparison Chart (online). Accessed 14/02/17. Includes information on Sweet’s syndrome.

Autoinflammatory Alliance (2016) Learn – Autoinflammatory Syndromes (online). Accessed 14/02/17. Provides general information.

National Institute of Arthritis and Musculoskeletal and Skin Diseases (2016) Understanding Autoinflammatory Diseases – The Immune System, NIH (online). Accessed 14/02/17.

Ngan, V. (2002) Behcet Disease. DermNet NZ (online). Accessed 14/02/17.

Oakley, A. (2015) Acute Febrile Neutrophilic Dermatosis. DermNet NZ (online). Accessed 14/02/17. Originally published 1998, and updated Sept 2015.

Oakley, A. (2015) Pyoderma Gangrenosum (online). Accessed 14/02/17. Originally published 1998, and updated Sept 2015.

© 2012-2017 Sweet’s Syndrome UK

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