Skip to main content
IDF logo
DNA helix illustration.

Bare lymphocyte syndrome type 1 and 2

Bare lymphocyte syndrome type 1 and 2 are forms of combined immune deficiencies (CIDs) characterized by a shortage of major histocompatibility complex (MHC) proteins.


Inheritance pattern: Autosomal recessive

Bare lymphocyte syndrome type 1

Bare lymphocyte syndrome type 1 is also known as MHC or HLA class 1 deficiency.

MHC molecules are important for presenting self and foreign proteins to the cells of the immune system. Individuals with low levels of MHC class 1 proteins are usually healthy during the first year of life. However, by late childhood, they can develop frequent upper and lower respiratory tract bacterial infections leading to lung damage and hearing loss. Granulomatous skin lesions are also a typical feature. A less-well-characterized group of affected individuals has an earlier presentation of symptoms, with recurrent bacterial, fungal, and parasitic infections in the first year of life. 

Most individuals with bare lymphocyte syndrome type 1 have low CD8+ T cells and decreased natural killer (NK) cell killing activity. A definite diagnosis can be made by looking for MHC class 1 proteins on the surface of peripheral blood mononuclear cells. Further genetic testing is then undertaken. 

Treatment is aimed at infection control with prompt antimicrobial therapy. Some individuals can benefit from Ig replacement therapy. Hematopoietic stem cell transplantation (HSCT) is not routinely used for bare lymphocyte syndrome type 1 because MHC class 1 protein expression is not restricted to hematopoietic stem cells, and, therefore, HSCT may not correct all disease manifestations. 

Find bare lymphocyte syndrome clinical trials

See if you qualify to participate in clinical trials evaluating new treatments and/or diagnostics for bare lymphocyte syndrome.

Bare lymphocyte syndrome type 2

Bare lymphocyte syndrome type 2 is also known as MHC or HLA class 2 deficiency.

Bare lymphocyte syndrome type 2 generally results in a clinical picture of CID since MHC class 2 proteins play a pivotal role in the maturation and function of both T and B cells. However, milder cases have been described. Most individuals present with viral, bacterial, fungal, and/or parasitic infections. Common symptoms include pneumonitis, bronchitis, gastroenteritis, and septicemia. Infections usually start in the first year of life and are associated with failure to thrive, diarrhea, and malabsorption. Those with bare lymphocyte syndrome type 2 commonly have the following abnormal laboratory findings: 

  • Low CD4+ T cell count. 
  • Low levels of immunoglobulin, and/or poor specific antibody responses to vaccines. 
  • Decreased T cell response to stimulation in the lab with stimulants like tetanus. 

There is a complete absence of MHC class 2 proteins on B cells and a slight decrease in MHC class 1 proteins. An attempt should be made to identify the exact genetic variant once an absence of MHC class 2 is observed. 

Therapy is supportive and is aimed at reducing infections with the administration of antibiotics and Ig replacement therapy. HSCT can resolve the immune deficiency. The chances for success are higher if the transplant is performed in the first two years of life. Individuals with MHC (HLA) class 2 deficiency generally die before five years of age without HSCT.

Learn more about combined immune deficiencies.

This page contains general medical and/or legal information that cannot be applied safely to any individual case. Medical and/or legal knowledge and practice can change rapidly. Therefore, this page should not be used as a substitute for professional medical and/or legal advice.

Adapted from the IDF Patient & Family Handbook for Primary Immunodeficiency Diseases, Sixth Edition 
Copyright ©2019 by Immune Deficiency Foundation, USA