Which immune response is primarily involved in graft-versus-host disease (GVHD)?

• A. CD4 response against the host
• B. CD8 response against the host
• C. Humoral response
• D. Innate immune response

Answer: (B)

Graft-versus-host disease (GVHD) occurs when donor immune cells recognize the recipient's tissues as foreign, leading to an immune attack. The primary immune response involved in this process is the CD8 T cell response against the host tissues. CD8 T cells, also known as cytotoxic T lymphocytes, are responsible for directly killing host cells that express foreign antigens. In the context of GVHD, these donor-derived CD8 T cells recognize and attack the host cells, resulting in tissue damage and the symptoms associated with GVHD.

While CD4 T cells, which help coordinate the immune response, can also be involved in GVHD, it is predominantly the CD8 T cell cytotoxic response that plays a central role in mediating the damage to the host's tissues. The humoral immune response, which involves B cells and antibody production, is not typically the main player in GVHD as the disease primarily results from T cell-mediated mechanisms. Similarly, the innate immune response does not specifically direct the graft-versus-host attack; rather, it is the adaptive immune T cells that are decisive here. This is why the CD8 T cell response is pivotal in the pathogenesis of GVHD.