alloréactives

Alloreactives is a term used to describe immune responses or immune cells that react against alloantigens—antigens derived from a genetically different individual of the same species. In transplantation biology, alloreactivity is a central factor determining whether a graft is accepted or rejected. The primary targets are often human leukocyte antigen (HLA) molecules.

Alloreactive T cells can recognize donor MHC in two main pathways. Direct allorecognition occurs when recipient T cells bind intact donor MHC molecules on donor antigen-presenting cells. Indirect allorecognition happens when donor-derived peptides are processed and presented by recipient APCs in the context of self MHC. A less common pathway, semi-direct recognition, involves transfer of intact donor MHC molecules to recipient APCs. Alloreactive B cells may produce alloantibodies against donor HLAs, contributing to antibody-mediated rejection.

Clinical relevance is highest in organ and hematopoietic stem cell transplantation. In solid organ transplantation, preformed or newly formed alloantibodies and T cell responses can lead to graft rejection. Crossmatching and panel reactive antibody testing are used to assess risk before transplantation. In hematopoietic stem cell transplantation, alloreactive T cells are implicated in graft-versus-host disease, though alloreactivity can also mediate beneficial graft-versus-leukemia effects.

Measurement of alloreactivity has included mixed lymphocyte reactions, cytotoxicity assays, and various antibody-based tests. Therapeutic strategies to modulate alloreactivity include HLA matching, immunosuppressive regimens, T cell depletion, and approaches aimed at inducing tolerance or blocking costimulation. See also alloantigen, allograft, and transplantation immunology.