Which cells are primarily involved in an acute graft-versus-host reaction?

In an acute graft-versus-host reaction (GVHR), the primary cells involved are CD4+ T cells and CD8+ T cells from the transplanted graft. These T cell populations recognize the recipient's tissues as foreign and mount an immune response against them.

The correct option highlights the involvement of specifically activated T lymphocytes, particularly those expressing CD45RO, which are memory T cells that play a crucial role in the acute phase of GVHR. These T cells, upon recognition of the major histocompatibility complex (MHC) molecules on the host tissues, proliferate and exert cytotoxic effects.

Neutrophils, while important in the inflammatory response, are not the main drivers of the acute GVHR. Instead, they are often recruited later in response to tissue damage and inflammation caused by T cell activity. The primary mediators of the graft-versus-host reaction remain the T lymphocytes.

Understanding the roles of these immune cells provides insight into the mechanisms underlying graft rejection and tolerance, both of which are critical considerations in transplantation medicine.