H2AB1 encodes an MHC class II β chain protein that functions as a critical component of the major histocompatibility complex class II (MHCII) system for antigen presentation. The protein forms heterodimers with MHC class II α chains to present peptides to CD4+ T cells, playing essential roles in adaptive immune responses 12. H2AB1 expression is upregulated in various pathological conditions including renal fibrosis, where it promotes CD4+ T cell activation and contributes to disease progression 1. In aging kidneys, H2AB1 expression increases as part of a 'tubuloinflammaging' phenotype associated with tubular cell senescence 3. The gene shows enhanced expression in pulmonary arterial hypertension, where it regulates endothelial cell proliferation, migration, and angiogenesis 2. In cancer, H2AB1 expression in tumor cells is crucial for CD4+ T cell-mediated antitumor responses, with loss of expression associated with treatment resistance 4. Cellular zinc availability through the transporter Zip14 is necessary for proper H2AB1 expression, as zinc deficiency leads to chrX remodeling and reduced transcription 5. The protein is also involved in autoimmune conditions like alopecia areata, where increased expression accompanies inflammatory infiltration 6.