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HLA Class II (DRB1, DQA1, DQB1) genotyping assesses inherited variants linked to susceptibility for immune‑mediated disease. The assay, also known as HLA class II typing or MHC class II genotyping, helps estimate genetic risk for conditions such as autoimmune thyroiditis, type 1 diabetes, systemic lupus erythematosus, autoimmune hepatitis, primary biliary cirrhosis, celiac disease, and chronic idiopathic urticaria. In reproductive immunology, results may inform evaluation of infertility and the risk of recurrent pregnancy loss. Results indicate predisposition rather than diagnosis. Interpretation is performed in clinical context and, when appropriate, in consultation with a genetics professional or relevant subspecialist.

The assay uses allele‑specific primers and real‑time PCR detection to identify polymorphisms in HLA class II genes, including DRB1, DQA1, and DQB1. HLA class II loci reside on the short arm of chromosome 6 within clusters such as DRA, DRB, DQA, DQB, DPA, and DPB and exhibit marked polymorphism (approximately 124 alleles described for DPB and over 440 for DRB). Each individual carries two alleles per locus, encoding alpha chains (from A‑designated genes) and beta chains (from B‑designated genes) that assemble into the class II HLA molecule on the cell surface. These molecules are primarily expressed on professional antigen‑presenting cells—macrophages, dendritic cells, and B lymphocytes—and participate in the genetic regulation of immune responses. HLA class II variants correlate with differential disease risk rather than deterministic outcomes. Illustrative associations include enhanced hepatitis B virus clearance in carriers of HLA‑DRB1*1302; increased type 1 diabetes risk with DQ8 and DQ2 (with greater risk when both are present); elevated rheumatoid arthritis risk with DR4; and a protective effect of DR2 among patients with rheumatoid arthritis. In reproductive medicine, HLA class II typing has been used to investigate infertility and recurrent pregnancy loss; in some couples, fewer shared HLA class II variants between partners has been associated with a higher likelihood of conception. However, current evidence does not support routine assessment of HLA genotype matching in the standard evaluation of recurrent pregnancy loss due to conflicting data and limited impact on management. Any therapeutic decisions are made by an immunologist or reproductive specialist after a comprehensive evaluation, and results are best interpreted with input from a clinical geneticist. Additional contexts include donor searches for hematopoietic stem cell transplantation and selection of blood components for highly immunized patients; such testing is typically performed in specialized centers. For this genetic analysis there is no concept of “normal” or “abnormal” result, as the assay characterizes gene polymorphism rather than measuring an analyte.