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Rbc & Wbc

Discussion in 'Medical Students - MD' started by SoFUnKyITsFrEsH, May 7, 2007.

  1. SoFUnKyITsFrEsH

    SoFUnKyITsFrEsH 2+ Year Member

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    Oct 2, 2006
    In class a few days ago my professor was explaining how most cells in our body contain a marker which distinguishes them as being apart of our bodies rather than foreign and possibly dangerous. He said that this marker was the glycoprotein MHC I. He also said that RBC did not contain this marker, so, I was wonder why our bodies don't attack our red blood cells (RBC). ((I know this forum was for med students only, but my professor is a Doctor and can't explain this)) Please help!
     
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  3. futureRXdealer

    futureRXdealer Junior Member 2+ Year Member

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    Denver, CO
    I am obviously not a med student so do not take my answer as truth in anyway. Let's see how much I remember from Anatomy.

    When T-cells encounter an APC, as you said, they check to see if its one of the bodies cells by and antigen on the MHC protein. T-cells respond to two types of MHC proteins.

    MHC I proteins- occur in every nucleated cell of the body, except erythrocytes. These proteins are produced by the cells and placed on the plasma membrane. On the way to the plasma membrane they pick up peptides in the cytoplasm and display them once they are on the plasma membrane. The immune system recognizes the peptides as its own cells and does not attack.

    MHC II proteins (HLA's)- Only occur on APCs and display foreign antigens.

    Cytotoxic T-cells respond to MHC-I while Helper T-cells respond to MHC-II.

    Since the erythrocytes do not present the MHC-I antigens on their surface, the
    body does not attack them.

    However, Anti-A & B antigens, packed RBC vs. Whole blood transfusions are a different senario. The body does not attack the blood cells but they begin to agglutinate.
     
  4. Critical Mass

    Critical Mass Guest

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    Feb 23, 2007
    Methinks normal erythrocytes in peripheral blood are enucleated.

    Help me out here, do people ever infuse whole blood? My impression was that donor blood was always separated into red cells and plasma, otherwise you'd be infusing anti A and B antibodies with type O RBC.
     
  5. futureRXdealer

    futureRXdealer Junior Member 2+ Year Member

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    Denver, CO
    I have no idea. That's where my knowledge comes to an end. When I was in anatomy we always discussed transfusions in terms of packed RBC's. In theory, I would not see a problem with transfusing whole blood if the blood types were a perfect match.
     
  6. Gut Shot

    Gut Shot 10+ Year Member

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    Short version:

    MHC Class I molecules present endogenous (from self) antigens to cytotoxic T lymphocytes. When they show a cytotoxic T lymphocyte an antigen that it doesn't recognize as self (as might happen if the cell is virally infected) the lymphocyte proceeds to kill the cell and destroy its contents. Hence, MHC I is a major player in the process of self/non-self discrimination. However, just because a given cell might lack MHC I expression does not mean it will automatically be seen and targeted for destruction.

    Why your body doesn't attack itself (or your RBCs) comes down to this recognition of self/non-self, which occurs during lymphocyte maturation. Nascent lymphocytes are exposed to various antigens that are present in your body, and the ones that show excessive binding and activation are eliminated before they are released into circulation.

    As a side note, people can and do make antibodies against their own red cells under various circumstances. For more info, please refer to your nearest textbook on transfusion medicine.
     
  7. Ultra7

    Ultra7 Member 5+ Year Member

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    Nov 15, 2005
    To my knowledge, whole blood is only used very rarely. Sometimes for very small infants where volume is a critical issue, I think they use whole blood to prime the ECMO machine.
    A major problem with transfusing whole blood (even if it is a perfect match) is the shelf life. PRBCs can last for weeks in the refrigerator, and plasma can be frozen. Platelets can't tolerate being that cold; normally platelets are kept for 3-5 days at RT and then discarded if not used. So whole blood only lasts a few days, which means you'd always be running out (especially since you'd need to match RBCs, platelets, and plasma).
     
  8. inside_edition

    inside_edition Waitlisted Member 2+ Year Member

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    simple answer (from a premed): if a cell doesn't have MHC's(or has very low levels of MHC expression) then that cell can present epitopes (aka peptides) to CD8/CD4 T cells. if there's no antigen presentation via MHC (plus the 2nd signal of CD80/86, i think), then an immune response is not mounted.

    also, low or no expression of MHC's is one of the possible reasons why cancer cells can sometimes escape an immune response.
     
  9. inside_edition

    inside_edition Waitlisted Member 2+ Year Member

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    if antibodies are not removed from the blood, then serum sickness results.
     
  10. Quincy

    Quincy 7+ Year Member

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    Dec 6, 2006
    Some viruses induce the down-regulation of MHC I so as to prevent Tc Cells from targeting the infected cell, but the LACK of MHC I also triggers cell targeting by Natural Killer cells.

    My understanding is that red blood cells aren't killed because of other RBC specific markers such as Rh and duffy.

    What I don't understand is why sperm aren't targeted (sperm also don't have MHC I).
     
  11. inside_edition

    inside_edition Waitlisted Member 2+ Year Member

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    some areas of the body are immunologically privileged such as the testes, uterus, the eye (which is why corneal transplants are so easily done), and a few other locations that i forgot.

    if damage occurs to some of these privileged areas, then the proteins released are recognized as foreign and an immune response is triggered.
     
  12. inside_edition

    inside_edition Waitlisted Member 2+ Year Member

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    if a virus results in downregulation of MHC I, then other forms of gene expression are probably altered, resulting in CD8 cytotoxic T cells attacking that cell.

    I did not know that a lack of MHC I expression results in activation of NK cells.
     
  13. Quincy

    Quincy 7+ Year Member

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    Dec 6, 2006
    I know, but sperm doesn't stay in the testes. is the whole tract from testes to urethra immunologically priveleged?
     
  14. Quincy

    Quincy 7+ Year Member

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    Dec 6, 2006
    but if other forms of gene expression are altered but there's no MHC I to present it, cytotoxic t cells can't do anything anyway. I'm 99% sure that lack of MHC I causes NK cells to destroy the cell, but I don't have my immunology text with me, so i could be wrong.
     
  15. inside_edition

    inside_edition Waitlisted Member 2+ Year Member

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    i'm not sure but maybe that's why semen contains lots of HIV viruses in HIV+ people.
     
  16. inside_edition

    inside_edition Waitlisted Member 2+ Year Member

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    oh yeah, that's true about MHC expression and CD8 T cells.

    what i learned was that NK cells can spontaneously kill cells infected with virus or tumor cells.
     
  17. Flopotomist

    Flopotomist I love the Chicago USPS 7+ Year Member

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    May 22, 2005
    NK cells also require 2 things before they can kill: Their KIR has to NOT recognize normal MHC1, AND an activating receptor must be present on the target cell before they will kill the target cell. This explains why an RBC isn't killed by an NK since the RBC doesn't have the activating receptor.

    I am still pretty foggy on this issue though, so people with stronger understandings feel free to correct me.
     
  18. Critical Mass

    Critical Mass Guest

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    Feb 23, 2007
    Not sure if I agree with this.

    BTW (as a general interest thing unrelated to this thread), I've been told that there are killer sperm in some species that function to wipe out sperm from other males.

    My sperm is definitely fitter than your sperm. :cool:
     
  19. For the time being, I wouldn't mind not having super sperm...less chance of my starting a basketball team.
    In a couple of years, different story, but for now you can keep your super sperm...get psyched to have a legion of kiddies!
     
  20. inside_edition

    inside_edition Waitlisted Member 2+ Year Member

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    i didn't know you were into interspecies sex
     
  21. Critical Mass

    Critical Mass Guest

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    Hey I'll take what I can get.

    Seems like from that other thread there might be a milf available out there somewhere.
     

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