The Fernandez reaction is a reaction that occurs to signal a positive result in the

lepromin The lepromin skin test is used to determine what type of leprosy a person is infected with. It involves the injection of a standardized extract of the inactivated "''leprosy bacillus''" (''Mycobacterium leprae'' or "Hansen's bacillus") under the ski ...

skin test for

leprosy Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria ''Mycobacterium leprae'' or ''Mycobacterium lepromatosis''. Infection can lead to damage of the nerves, respiratory tract, skin, and eyes. This nerve damag ...

. The reaction occurs in the skin at the site of injection if the body possesses antibodies to the Dharmendra antigen, one of the

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune respons ...

s found in

Mycobacterium leprae ''Mycobacterium leprae'' (also known as the leprosy bacillus or Hansen's bacillus), is one of the two species of bacteria that cause Hansen’s disease (leprosy), a chronic but curable infectious disease that damages the peripheral nerves an ...

, the bacteria that causes leprosy. The reaction occurs via a delayed-type

hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. They are usually referred to as an over-reaction of the immune ...

mechanism. This reaction occurs within 48 hours of injection of

and is seen in only tuberculoid forms of leprosy. This represents a delayed-type hypersensitivity reaction. In contrast, the Mitsuda reaction (delayed granulomatous lesion) occurs 3–4 weeks after injection of

and is only seen in patients with the tuberculoid form of leprosy (not the lepromatous form, in which the body does not mount a strong response against the bacterium). In terms of mechanism of action and appearance, the reaction is similar to the

tuberculin Tuberculin, also known as purified protein derivative, is a combination of proteins that are used in the diagnosis of tuberculosis. This use is referred to as the tuberculin skin test and is recommended only for those at high risk. Reliable admi ...

reaction of a positive

Mantoux test The Mantoux test or Mendel–Mantoux test (also known as the Mantoux screening test, tuberculin sensitivity test, Pirquet test, or PPD test for purified protein derivative) is a tool for screening for tuberculosis (TB) and for tuberculosis diagn ...

for

tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, i ...

.Thomas J, Joseph M, Ramanujam K, Chacko CJ, Job CK. Histology of the Fernandez reaction. An appraisal. Int J Lepr Other Mycobact Dis. 1981 Mar;49(1):1-8. PMID 7195878.

References

Skin tests Leprosy {{Immunology-stub