Basic concepts of transplantology
To understand transplantation processes, one must be fluent in basic terminology. Any transplantation act involves the following elements and subjects:
- Transplant — directly the area of tissue or the whole organ that undergoes transplantation.
- Donor — an individual (organism) from which material is harvested for subsequent transfer.
- Recipient — the organism receiving the transplanted material.
Autotransplantation: transplantation to oneself
In autotransplantation, the transfer is carried out within the same organism. That is, the donor and the recipient are the same person.
This is the most successful and reliable type of transplantation. Since the tissues are genetically identical, antigenic incompatibility is completely absent. This ensures true engraftment of the transplant. The main task of the surgeon in this case remains ensuring adequate blood supply to the transplanted area in its new location.
This type is widely used in reconstructive medicine. Examples include:
- Transplantation of skin, muscles, cartilage, tendons, nerves, and blood vessels.
- Use of the omentum.
- Plastic surgery of the face (correction of cleft lip and cleft palate, rhinoplasty).
- Restoration of structures such as the esophagus, larynx, and genital organs.
- Corneal transplantation.
Allotransplantation: within the same species
Allotransplantation (also known as homotransplantation) involves the transfer of tissues between different individuals belonging to the same biological species.
The main problem of this method is antigenic differences between the donor and recipient. Due to the immune response, such a transplant does not take long-term and is eventually rejected. However, exceptions exist in nature: for example, in some worms and hydras, such transplants are successful.
To increase the chances of success in medicine, special variants of allotransplantation are used:
- Isotransplantation — transplantation between identical (monozygotic) twins.
- Syntransplantation — transplantation from first-degree relatives.
Xenotransplantation and explantation
Xenotransplantation (heterotransplantation) is the transfer of material between members of completely different biological species. Due to the colossal antigenic difference, this method can only be successfully implemented in natural conditions in some species of invertebrate animals.
Separately, explantation is distinguished. This method is fundamentally different from the previous ones, as it does not involve transplantation into another living organism. Explantation is the cultivation (growing) of isolated cells, tissues, organs, or even whole organisms in an artificial environment outside the body.
Briefly: answers to topical questions
What are the clinical types of transplant rejection depending on the time of their development?
Depending on the time of development, three clinical types of transplant rejection are distinguished.
- Hyperacute rejection — develops on days 1–5. Its cause is the presence of preformed antibodies in the recipient (due to sensitization to AB0 or HLA).
- Acute rejection — occurs within 5 to 30 days. The main mechanism is the activation of cellular immunity.
- Chronic rejection — develops after 6 months or more. The mechanism of transplant damage is also predominantly cellular.
Which groups of immunosuppressive drugs are used to prevent allograft rejection?
To prevent allograft rejection, the following immunosuppressive agents are indicated in sources:
- Cyclic antibiotics: cyclosporine, tacrolimus (FK506), and rapamycin. Cyclosporine and tacrolimus interrupt Ca2+-dependent signal transduction, block NF-AT translocation into the nucleus, and thereby prevent cell activation, interleukin-2 synthesis, and T-lymphocyte clonal expansion. Rapamycin blocks signal transduction from the IL-2 receptor.
- Polyclonal antibodies: antilymphocyte sera and antilymphocyte globulin directed against lymphocyte membrane molecules.
- Monoclonal antibodies: antibodies against specific T-lymphocyte membrane antigens; for antibodies against the CD3 molecule, only blocking antibodies are used in therapy.
What are the criteria for diagnosing brain death when harvesting organs from a cadaveric donor?
The criteria for diagnosing brain death are clinical and instrumental signs of irreversible damage.
- Loss of consciousness — a persistent and irreversible state.
- Impairment of brainstem functions — absence of spontaneous breathing and swallowing, as well as impaired systemic hemodynamics.
- Areflexia — absence of pupillary, pharyngeal, and other reflexes.
The diagnosis is necessarily confirmed instrumentally: using electroencephalography (absence of bioelectrical activity) and angiography or ultrasound duplex scanning (confirmation of the cessation of cerebral blood flow).
What does the term "orthotopic transplantation" mean as opposed to heterotopic?
Orthotopic transplantation implies the transplantation of a donor organ into its natural anatomical position.
| Type of transplantation | Characteristic |
|---|---|
| Orthotopic | Transplantation of an allogeneic organ in place of the recipient's own removed organ (in the normal bed). |
| Heterotopic | Placement of a donor organ in another area of the recipient's body (for example, in another area of the abdominal cavity, in the pelvis, or on the thigh). |
Types are easy to remember by prefixes: Auto- — "self" (to oneself). Allo- — "other" (to another person/individual of the same species). Xeno- — "alien" (to another species). Ex- — "outside" (outside the body).
Class and exam questions
Why is autotransplantation considered the most successful method?
In autotransplantation, the donor and recipient are the same organism. Due to this, there is no antigenic incompatibility, the immune system does not attack the tissues, and true engraftment occurs.
What is the main condition for autograft engraftment?
The most important condition for the transplantation of one's own tissues is the technical provision of adequate blood supply and nutrition to the transplanted area in its new location.
How does isotransplantation differ from standard allotransplantation?
Isotransplantation is a specific, most favorable case of allotransplantation, in which the donor is the recipient's identical twin. This minimizes antigenic differences, unlike transplantation from an unrelated person.
What else to study on this topic
- Mechanisms of antigenic incompatibility during tissue transplantation
- Features of blood supply and nutrition of transplants in a new location
- In vitro tissue culture technologies (explantation)
- The phenomenon of successful homotransplantation in hydras and worms
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