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Rh factor: Give patient Rh-immune globulin. How does that work?

Discussion in 'MCAT Study Question Q&A' started by SaintJude, 05.01.12.

  1. SaintJude

    SaintJude

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    Kaplan:

    Does this mean that Rh-immune globulin shots will kind of "give" the mother RH+ antigens? How come the body won't recognize these Rh-immune globulins as "foreign" and destroy them?
    Last edited: 05.01.12
  2. hellocubed

    hellocubed

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    Yeah, I read both Kaplan and EK and am fairly confused by Kaplan's explanation.

    Because, if you give the mother Rh antibodies, are they saying that they "block" the Rh antigens of the baby? It seems unlikely, considering new blood cells are continually being made.


    EK says that the baby needs to be given a COMPLETE Rh- blood transfusion. Which seems dangerous, but more logical.
  3. SaintJude

    SaintJude

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    The strategy that EK mention does indeed work, but is only a back-up for Kaplan's suggested strategy. Hopefully a med student or attending will help answer this question
  4. MedPR

    MedPR

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    The exogenous antibody has a greater affinity for the Rh antigen than the antibodies produced by the mother. Basically it binds up all the antigens before the mother's immune system even knows what happens. Therefore, the mother is never really exposed to the antigen = the antigen is never able to elicit an immune response = the mother doesn't have antibodies against future RH+ fetuses.
  5. SaintJude

    SaintJude

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    :thumbup: Brilliant! The exogenous immunoglobulin binds all the antigens presented by the Rh+ fetus--that's amazing.
  6. DrRichand1

    DrRichand1

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    The only time the mother would have to worry about rh is when she is Rh- and her baby is Rh+. all other combinations don't matter cuz if she's Rh+ then she will not make antibodies.
    Since fetal and paternal blood don't mix during pregnancy i'm asumming antibodies made by an Rh- mother during a second pregnancy would cross this barrier. Is that correct?
  7. MedPR

    MedPR

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    You meant maternal blood, right?

    The reason the first pregnancy isn't usually a problem is because, as you say, fetal and maternal blood typically do not mix before labor. They can, however, mix during labor, which is why subsequent pregnancies can be a problem for Rh- mothers. I'm a little fuzzy on this part, but I believe they do fetal and maternal blood tests before birth and if the mother is Rh- and fetus Rh+ then RhoGAM is administered prior to birth. Thus, if there is blood transfer during delivery, RhoGAM binds up the Rh-antigens from the fetal blood and the Rh- mother has an immune response.

    Unlike IgG, RhoGAM does not cross the placenta so it isn't an issue for the fetus.
  8. Morsetlis

    Morsetlis SGU MS-4

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    You mean, like IgG, the RhoGAM DOES cross the placenta.

    Unlike IgG, the RhoGAM does not have an exposed specific Fc portion that can activate the human complement system which leads to the formation of a Membrane Attack Complex that mediates osmotic lysis of the fetal red blood cells.

    "Hello, I am a baby red cell. On me is an antigen. Its called Rh+.

    Hi, I am mom's immune system. I don't know what this Rh+ is all about. I've never seen it before, I don't like it, and so, I think its foreign. MOUNT UP! (This is mom's immune system recognizing that a foreign antigen has entered her system, and forms IgM and then eventually IgG with memory cells against that antigen, much like any antigen would do)

    Hello, I am a baby red cell from baby #2. On me is an antigen. Its called Rh+.

    Hi, I am moms... THAT LITTLE ****ER! HE'S BACK AGAIN!? KILL THAT MOTHER ****ER! I TOLD YOU... NOT IN MY HOUSE! (Mom's immune system, having already been sensitized mounts an immediate IgG response against baby's red blood cells, having recognized this not just as foreign, but as an already-encountered known "bad guy")

    Hi, I'm RhoGam. I'm sort of like Frodo's elven cloak of invisibility. For those of you a little bit older, "Ninja!" (smoke grenade) "Vanish!" (RhoGam has the Fab portion of the antibody against Rh+... you know, the V part of the Y... so it binds to Rh+ really well. What it lacks is the Fc component... you know the | part of the Y... so it doesn't do anything once its bound.

    Hi, I a moms immune system. I could have SWORN there was that Rh+ thing back here again. Now where did he go... Well, I dont see that antigen anymore, there's nothing for my Fab to bind to. And, I don't see any signal from my Fc communicator, so none of my Fab's have bound to anything. Oh well, false alarm.

    So you see, it has nothing to do with dosage of antibody/immunoglobulin, what it has to do is with the functionality of the antibodies doing the binding. IgM cannot cross the placenta, so the initial baby is unharmed. IgG CAN cross the placenta, and has Specificity to identify the Rh-Anti-D Antigen via its Fab portion. The normal IgG Fc portion summons the rest of the immune response, mostly via complement activation, but also by identification to macrophages to consume and destroy the red cell. This IgG from Mom, the one with a functional Fab and Fc portion, that CAN cross the placenta, marks all of the baby's red blood cells for death.

    Inject RhoGam-D. This is a rhesus antibody that matches mom's antibodies in almost every way. IgG, so it crosses the placenta. Specific for Rh-Anti-D Antigen via Fab portion, so it binds to baby's red blood cells. BUT, it has a nonfunctioning Fc portion (mom's immune system doesn't know what to do with Rhesus Fc) so no immune response is summoned. So, the antigen is protected ("hidden") by the binding of antibody, but the cell is not destroyed since the Fc portion doesn't work (thus Frodo's cloak of invisibility). "
  9. SaintJude

    SaintJude

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    This right here will be my favorite post of the year. And it' makes so much sense. How amazing is that IgM cannot cross the placenta, but IgG can. So cool. Thank you!!!
  10. MedPR

    MedPR

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    Oh I see, so it does cross the placenta but doesn't do anything but bind the antigen.

    I just assumed it didn't cross the placenta (even though that doesn't make sense since it is an IgG) because I figured if it did, it would have the same effect as maternal antibodies.

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