Natural killer (NK) cells

A. Regulatory T cells:Regulatory T cells suppress immune responses and promote tolerance to self and foreign antigens. They help prevent excessive immune reactions, including tissue rejection, making them least likely to cause rejection after an organ transplant.

B. Natural killer cells:NK cells can recognize and destroy cells lacking normal MHC expression, including transplanted tissue. They contribute to early immune responses that may lead to graft rejection.

C. B cells:B cells produce antibodies against foreign antigens on transplanted tissue, leading to humoral-mediated rejection. Their activity can directly damage the graft and trigger complement-mediated injury.

D. Cytotoxic T cells:Cytotoxic T cells recognize foreign MHC molecules on transplanted tissue and destroy those cells. They play a central role in cellular-mediated graft rejection and are a major contributor to transplant failure.

E. Macrophages:Macrophages are recruited to the graft site, where they participate in inflammation, antigen presentation, and tissue destruction. Their activity supports both cellular and humoral mechanisms of transplant rejection.

A. The subcapsular sinus:The subcapsular sinus is the space just beneath the capsule of a lymph node where lymph first enters from the afferent vessels. It does not serve as an exit pathway.

B. The cortical sinus:The cortical sinuses are channels within the cortex that allow lymph to percolate through the lymph node, facilitating interaction with lymphocytes and macrophages. They are internal pathways, not exit points.

C. Afferent lymphatic vessels:Afferent lymphatic vessels bring lymph intothe lymph node from peripheral tissues. They are entry vessels, not exit vessels.

D. Efferent lymphatic vessels:Efferent lymphatic vessels carry lymph out ofthe lymph node at the hilum after it has been filtered and exposed to immune cells. They are the correct exit pathway for lymph leaving the node.