Direct and indirect alloantigen recognition are two mechanisms by which T cells may recognize alloantigens and lead to transplant rejection after an organ transplant.
Contents
Direct alloantigen recognition
Donor tissue dendritic cells migrate to lymph nodes, stimulating a measurable percentage of recipient T cells. The host T cells in the lymph node recognize either the allograft HLA or an associated bound peptide.
In this case, alloreactive T cells are stimulated by donor APCs which express both the allogeneic MHC and costimulatory activity.
Indirect alloantigen recognition
Host (organ-recipient) dendritic cells process proteins from the transplanted graft, and trigger a T cell response. Presentation may occur via MHC class I or MHC class II, although class II is usually involved.
The main difference between indirect and direct alloantigen recognition stems from the origin of the macrophages (type of APC). In direct alloantigen recognition, the involved dendritic cells are donor derived. In indirect alloantigen recognition, the dendritic cells (APCs) involved are recipient APCs.