Type I interferon-stimulated gene (ISG) that plays a critical role in antiviral and antibacterial activity. During bacterial infection, promotes macrophage differentiation and facilitates inflammatory cytokine secretion (By similarity). Plays a role in the control of respiratory syncycial virus/RSV infection, reducing the ability of the virus to replicate (PubMed:32611756). Acts as a feedback regulator of IFN responses by negatively regulating IKBKB kinase activity through interaction with FKBP5 (By similarity). Precursor of the histocompatibility antigen HA-28 in BALB.B mice. More generally, minor histocompatibility antigens refer to immunogenic peptide which, when complexed with MHC, can generate an immune response after recognition by specific T-cells. The peptides are derived from polymorphic intracellular proteins, which are cleaved by normal pathways of antigen processing. The binding of these peptides to MHC molecules and its expression on the cell surface can stimulate T-cell responses and thereby trigger graft rejection or graft-versus-host disease (GVHD). More specifically, HA-28 minor antigen is transcribed in the BALB.B donor but not in host C57BL/6 cells. HA-28 is presented to the donor BALB.B cell surface by Kb MHC. This complex HA-28/Kb MHC elicits cytotoxic T-cell response in C57BL/6 mice immunized with BALB.B spleen cells. It induces C57BL/6 mice cells recognition and lysis by CD8 T-cell from BALB.B mice. HA-28 antigen forms a complex with Kb MHC in BALB.B donor cells. Interacts with FKBP5; this interaction modulates IKBKB and IKBKE kinase activities (By similarity). Expressed on cells of the hematopoietic lineage. Detected in transformed cell lines of the macrophage and B-cell lineage. Expressed in spleen and bone marrow. By respiratory syncytial virus/RSV (PubMed:32611756). HA-28 antigen is expressed after induction by inflammatory cytokines. Deletion mutants result in elevated respiratory syncycial virus/RSV infection in vitro. Belongs to the IFI44 family.