HLA-DRB1 and rheumatoid arthritis: Furthermore, when stimulated by IFNγ ex vivo, bone marrow-derived macrophages from non-immunized transgenic (Tg) mice that carried the DRB1*03:01 allele presented activation of UPR and proteasomal degradation, reduction of intracellular ATP levels, as well as enhanced TNF-α and nitrite production, as compared to the Tg mice carrying the RA predisposing DRB1*04:01 allele and the RA-protective DRB1*04:02 alleles.