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CIITA gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

CIITA gene

The CIITA gene acts as a master regulator for immune system genes, ensuring the body can effectively recognize and fight off foreign invaders like bacteria and viruses.

Normal Function

The CIITA gene provides instructions for making a protein that controls the activity (transcription) of major histocompatibility complex (MHC) class II genes. This protein is critical for the production of MHC class II proteins.

MHC class II proteins are found on the surface of immune cells, such as lymphocytes. They function by binding to protein fragments (peptides) from foreign invaders like bacteria, viruses, and fungi. By presenting these fragments to other immune cells, they trigger an immune response to eliminate the threat.

The CIITA protein also plays a secondary role in enhancing the transcription of MHC class I genes, which help the body identify and attack infected cells.

Health Conditions Related to Genetic Changes

Bare lymphocyte syndrome type II

More than a dozen mutations in the CIITA gene cause bare lymphocyte syndrome type II (BLS II), a form of combined immunodeficiency (CID).

  • Mechanism: Mutations result in a lack of functioning CIITA protein, which prevents the production of MHC class II proteins.
  • Impact: Without these proteins on the surface of immune cells, the body cannot effectively recognize or clear foreign invaders.
  • Symptoms: Affected individuals have virtually no immune protection, leading to persistent and life-threatening respiratory, gastrointestinal, and urinary tract infections.

Autoimmune Addison disease

The CIITA gene has also been associated with Autoimmune Addison disease.

Other Names for This Gene

  • C2TA
  • CIITAIV
  • MHC class II transactivator
  • MHC2TA
  • NLR family, acid domain containing
  • NLRA
  • nucleotide-binding oligomerization domain, leucine rich repeat and acid domain containing

Frequently Asked Questions

Management focuses on preventing infections and supporting immune function. Prophylactic antibiotics, antifungal agents, and immunoglobulin replacement therapy (IVIG) are commonly used. Hematopoietic stem cell transplantation (HSCT) can provide a curative option for selected patients, especially those with severe combined immunodeficiency phenotypes. Ongoing monitoring for autoimmune complications, such as Addison disease, is also recommended.
Most heterozygous carriers are asymptomatic because one functional copy of CIITA usually provides sufficient MHC II expression. However, rare reports suggest that carriers might have a modestly increased risk for autoimmune conditions, such as autoimmune Addison disease, though the absolute risk remains low. Genetic counseling is advised for families planning future pregnancies.
Yes. Because CIITA deficiency impairs MHC II‑mediated antigen presentation, patients often have poor antibody responses to protein‑based vaccines (e.g., tetanus, pneumococcal). Live attenuated vaccines are generally avoided due to infection risk. Immunization schedules should be individualized, and serologic testing after vaccination can help assess protective immunity.
Diagnosis usually begins with a clinical history of severe, recurrent infections and laboratory findings of absent or markedly reduced HLA‑DR (MHC II) expression on peripheral blood lymphocytes. Confirmatory testing includes flow cytometry for MHC II proteins, functional assays of antigen presentation, and molecular genetic sequencing of the CIITA gene to identify pathogenic variants.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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