In graft-versus-host disease, which cells are typically responsible for attacking host tissues after bone marrow transplant?

• A. Recipient B cells
• B. Donor T lymphocytes (CD4+ and CD8+)
• C. Donor B cells
• D. Recipient dendritic cells

Answer: (B)

Donor T lymphocytes are the main culprits in graft-versus-host disease after allogeneic bone marrow transplant. These mature donor T cells recognize host tissues as foreign because of differences in HLA antigens, become activated (with help from host antigen-presenting cells), and then attack the host’s cells. Both CD4+ helper and CD8+ cytotoxic T cells participate—CD4+ cells orchestrate the response and sustain inflammation, while CD8+ cells mediate direct killing of host cells. This T cell–driven attack explains the classic acute GVHD targets (skin, liver, and gut). While donor-derived T cells are the primary effectors, host antigen-presenting cells initiate the activation by presenting host alloantigens. B cells and recipient dendritic cells are not the principal drivers of acute GVHD.