IMMUNOLOGY

Detailed explanation-1: -Transplant rejection is a process in which a transplant recipient’s immune system attacks the transplanted organ or tissue.

Detailed explanation-2: -In most cases, adaptive immune responses to the grafted tissues are the major impediment to successful transplantation. Rejection is caused by immune responses to alloantigens on the graft, which are proteins that vary from individual to individual within a species, and are thus perceived as foreign by the recipient.

Detailed explanation-3: -Hyperacute rejection is usually caused by specific antibodies against the graft and occurs within minutes or hours after grafting. Acute rejection occurs days or weeks after transplantation and can be caused by specific lymphocytes in the recipient that recognize human leukocyte antigens in the tissue or organ grafted.

Detailed explanation-4: -T cell activation is central to graft rejection. Tissue destruction occurs due to direct T cell-mediated lysis of graft cells, T cell activation of accessory cells, alloantibody production, and/or complement activation.

Detailed explanation-5: -There are three major types of allograft rejection: Hyperacute, acute, and chronic rejection.

Detailed explanation-6: -Type II hypersensitivity reaction refers to an antibody-mediated immune reaction in which antibodies (IgG or IgM) are directed against cellular or extracellular matrix antigens, resulting in cellular destruction, functional loss, or tissue damage.