(A) B cells

(B) T cells

(C) Macrophages

(D) Eosinophils

T cells are responsible for graft rejection. These adaptive immune cells recognize foreign MHC antigens on the donor graft, triggering cell-mediated cytotoxicity and inflammation that destroy transplanted tissue.

Options Explained

B Cells (A)

B cells mediate humoral immunity via antibody production, contributing to chronic or hyperacute rejection through alloantibody formation. However, they are not the primary effectors of acute graft rejection, which is T cell-dominated.​

T Cells (B)

CD4+ helper T cells activate macrophages and support cytotoxic responses, while CD8+ cytotoxic T cells directly kill graft cells expressing foreign MHC. Allorecognition via direct (donor APCs) or indirect (recipient APCs) pathways drives acute rejection.

Macrophages (C)

Innate immune macrophages amplify inflammation via cytokines and phagocytosis but require T cell activation (via IFN-γ). They contribute to chronic rejection but cannot independently reject grafts.​

Eosinophils (D)

Eosinophils target parasites and allergies via granule proteins, playing no significant role in solid organ transplant rejection mechanisms.​

T cells drive graft rejection through MHC allorecognition, a critical concept for understanding transplant immunology in medical entrance exams like NEET.​

Graft Rejection Mechanisms

Acute rejection involves T cell infiltration: CD8+ cells lyse targets via perforin/granzyme; CD4+ cells recruit effectors via IFN-γ/CXCL10. Immunosuppressants like calcineurin inhibitors target T cell activation.​

Types of Rejection

• Hyperacute: Preformed antibodies (minutes-hours).

• Acute: T cell-mediated (days-weeks).

• Chronic: Fibrosis, antibodies (months-years).​

Why Option (B) is Correct

Standard immunology confirms T cells as necessary and sufficient for allograft rejection; T cell-deficient models accept grafts until reconstitution.