Bare lymphocyte syndrome type 1 and 2

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.