This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
[{'content': 'HLA associated with rheumatoid ahritis - \nSelect and explain. \nA. DR1, B. DR2, C. DR3, D. DR4', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The human leukocyte antigen (HLA) system or complex is a gene complex encoding the major histocompatibility complex (MHC) proteins in humans. These cell-surface proteins are responsible for the regulation of the immune system in humans. The HLA gene complex resides on a 3 Mbp stretch within chromosome 6p21. HLA genes are highly polymorphic, which means that they have many different alleles, allowing them to fine-tune the adaptive immune system. The proteins encoded by ceain genes are also known as antigens, as a result of their historic discovery as factors in organ transplants. Different classes have different functions:HLA-DR4 (DR4) is an HLA-DR serotype that recognizes the DRB1*04 gene products. The DR4 serogroup is large and has a number of moderate frequency alleles spread over large regions of the world.', 'role': 'assistant'}]