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Learning objectives

  • Explain why human leukocyte antigens (HLAs) are important in tissue transplantation
  • Explain the types of grafts possible and their potential for interaction with the immune system
  • Describe what occurs during graft-versus-host disease (GVHD)

A graft is the transplantation of an organ or tissue to a different location, with the goal of replacing a missing or damaged organ or tissue. Grafts are typically moved without their attachments to the circulatory system and must reestablish these, in addition to the other connections and interactions with their new surrounding tissues. There are different types of grafts depending on the source of the new tissue or organ. Tissues that are transplanted from one genetically distinct individual to another within the same species are called allograft s . An interesting variant of the allograft is an isograft , in which tissue from one twin is transplanted to another. As long as the twins are monozygotic (therefore, essentially genetically identical), the transplanted tissue is virtually never rejected. If tissues are transplanted from one area on an individual to another area on the same individual (e.g., a skin graft on a burn patient), it is known as an autograft . If tissues from an animal are transplanted into a human, this is called a xenograft .

Transplant rejection

The different types of grafts described above have varying risks for rejection ( [link] ). Rejection occurs when the recipient’s immune system recognizes the donor tissue as foreign (non-self), triggering an immune response. The major histocompatibility complex markers MHC I and MHC II , more specifically identified as human leukocyte antigens (HLAs) , play a role in transplant rejection. The HLAs expressed in tissue transplanted from a genetically different individual or species may be recognized as non-self molecules by the host’s dendritic cells . If this occurs, the dendritic cells will process and present the foreign HLAs to the host’s helper T cells and cytotoxic T cells, thereby activating them. Cytotoxic T cells then target and kill the grafted cells through the same mechanism they use to kill virus-infected cells; helper T cells may also release cytokines that activate macrophages to kill graft cells.

Types of Tissue and Organ Grafts and Their Complications
Graft Procedure Complications
Autograft From self to self No rejection concerns
Isograft From identical twin to twin Little concern of rejection
Allograft From relative or nonrelative to individual Rejection possible
Xenograft From animal to human Rejection possible

With the three highly polymorphic MHC I genes in humans ( HLA-A , HLA-B , and HLA-C ) determining compatibility, each with many alleles segregating in a population, odds are extremely low that a randomly chosen donor will match a recipient's six-allele genotype (the two alleles at each locus are expressed codominantly). This is why a parent or a sibling may be the best donor in many situations—a genetic match between the MHC genes is much more likely and the organ is much less likely to be rejected.

Questions & Answers

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Lissa Reply
microorganism functions
NUHU Reply
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Erick Reply
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Allan
Hlo
SUMIT
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when the stomach is been affected with helicobacteria what are the preventive measure to be considered to ensure specific outcome?
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Ayan
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Nanjoh
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vijay Reply
microbiology is the scientific study of microorganisms .microorganisms are those organisms that are too small to see with the naked eye ex-bacteria fungi
Yashkin
a branch of biological science concerned with organisms that can not be observed with a naked eye
Mooya
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lord
polymorpho nuclear leukocyte, known as granulocyte are divide into three,1-polymorpho eosinophil 2-polymorpho basophil 3-polymorpho neutrophil
Musa
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Emma
microbiology is the scientific study of microorganisms
Atia
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Ama Reply
blood collection and urinarysis
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2143
Lizzy
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Lizzy
In the periodic table the number on the upper left hand side is what
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Hydrogen
Tob
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Aurelia
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Aurelia
hologen
Usman
differences between acid fast and non acid fast bacilli
ANTHONY Reply
acid fast have cell wall that holds to carbol fuschin stain while non acid fast doesn't have. it readily releases out the primary stain the carbol fuschin.
LAFIA
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eklectc
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Olivia
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LAFIA
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eklectc
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eklectc
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chima
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Tanaka
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Eddy
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good hygiene
Dhaqan
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henry
maintenance of sterilization
Pooja
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Faustina
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Md
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أ‌) Host factor ب) pathogen ج) environment
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kalai
The epidemiologic triangle is made up of three parts: agent, host and environment
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penicillium notatum
Pooja
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penicillium fungi
Pooja
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Usman
Why can we see ourselves in a mirror?
Usman
mention 5 characteristics of prokaryotic cell and also 5 characteristics of euryotic cell
Grace Reply
PROKARYOTES _ does not have nucleus _does not have membrane bound organels like eukaryotes -does not have endoplasmic reticulum _does not have a mitchochondrion _it have plasmid instead of chromosome EUKARYOTE S _have true nucleus _have all membrane bound organels _have mitochondria have
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explanation of spores
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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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