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Malcolm Needs

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Everything posted by Malcolm Needs

  1. Thanks for those suggestions, but PLEASE, don't call it anti-Kell and anti-Cellano!
  2. True, but, in the early days, I know of at least one example that caused almost pure red cell aplasia in a BMT from a group A donor, because the contaminating anti-A was so strong.
  3. Phew, that's a difficult one! You could begging some from one of the world's big organisations, such as the International Blood Group Reference Laboratory in the UK, somewhere like the Mayo Clinic in New York, Amsterdam, South Africa, etc, but other than that, I don't know. Some of the large reagent suppliers, such as Ortho or BioRad may possibly have some in store too.
  4. I must admit, we always used to use polyclonal antibodies, and there is a reason for this. Even blended monoclonal antibodies will still only recognise certain epitopes within the antigen, and while the K and k antigens tend to be single amino acid substitutions of methionine at position 193 for the K antigen, and threonine at position 193 for the k antigen, this is by no means universal. A weak expression of K is seen when either an argenine or a serine residue replace the methionine residue at position 193. As with amino acid substitutions leading to weakened expression of the K antigen, so the same can happen with the k antigen, but these substitutions may not actually be at position 193. A recent publication has shown that a substitution of Leu196Val weakens the expression of the k antigen (see Uchikawa M, Onodera T, Tsuneyama H, Enomoto T, Ishijima A, Yuasa S, Murata S, Tadokoro K, Nakajima K, Juji T. Molecular basis of unusual Kmod phenotype with K+wk-. Vox Sang 2000; 78 Suppl. 1: Abstract O011, Poole J, Warke N, Hustinx H, Taleghani BM, Martin P, Finning K, Crew VK, Green C, Bromilow I, Daniels G. A KEL gene encoding serine at position 193 of the Kell glycoprotein results in expression of KEL1 antigen. Transfusion 2006; 46: 1879-1885 and Millard GM, Lopez GH, Turner EM, Lizarazu ME, Roots NM, Liew Y-W, Flower RL, Hyland CA. Modified expression of the KEL2 (k) blood group antigen attributed to p.Leu196Val amino acid change three residues from the K/k antigen polymorphism site: implications for donor screening. Transfusion 2019; 59: 1156-1158.). Therefore, it is more likely that you may get a false negative result using a monoclonal antibody in adsorption/elution tests, than by using a polyclonal antibody, with its wider breadth of specificity to the antigen's epitopes.
  5. I can see no reason why this would not work as a method. We used to use something very similar when testing individuals expressing the "McLeod" phenotype. However, these days it would be easier (and certainly more accurate) to perform gene sequencing on both the KEL and the XK genes. Don't forget that a true Duffy null phenotype (FY/FY), as opposed to a "GATA-1" type Fy(a-b-) is, these days, established by molecular techniques.
  6. I have been thinking about this and I have come, more or less, to the same way of thinking as Neil Blumberg. The first pregnancy almost certainly could not have caused sensitisation of most of the common antigens, as some would not be formed on the foetal red cells at 10 weeks of gestation, while, even with a huge foeto-maternal haemorrhage (FMH) (in terms of the ratio of the total foetal red cell mass), the actual volume of foetal red cells transferred to the maternal circulation would not be sufficient to cause sensitisation in anyone but a person who is a "super responder". The second pregnancy could easily have caused a primary response, either at partum, or as a result of a chronic FMH throughout much of the pregnancy. Unless the woman's antibody screen was performed at about six months post-partum, such antibodies may never have been detected at their peak, and then may have declined to levels where normal serological techniques would not detect them. Of course, all of this is theoretical, but, given the fact that the mother is probably an R1R1 (from information given above), it is most unlikely that an FMH estimation, such as a Kleihauer test was performed, or that the mother would have been serologically "followed up". You also do not give the woman's transfusion history. It would be helpful to know the time between the second and third pregnancy, and also, of course, if the same male was the biological father in both pregnancies. This latter piece of information may actually be very difficult indeed to ascertain, as the woman may not wish to disclose her sexual history. It is not unknown for antibodies of a particular specificity (say, purely for example, an anti-Jka) to increase in strength (as measured by serial titres) during a pregnancy that is, in this example, Jk(a-). This is more common in a pregnancy where there is at least one other specificity (let us say, again, just as an example, anti-K), where (again, just as an example) the foetal red cells do express the K antigen, but not the Jk(a) antigen. Lastly, antibodies that are forming de novo, very often seem to cross-react with antigens to which they are not actually stimulated. This is true, even in the case of some monoclonal antibodies (particularly those within the HLA system), but some antibodies (again, even monoclonal antibodies) maintain what I will call a pseudo-specificity even in the "mature state". This includes monoclonal anti-D. Thorpe et al have reported that monoclonal anti-D molecules possess a V4-34 moiety, that is also present in anti-I and anti-i, which is why these reagents should never be used straight from the fridge (Thorpe SJ, Boult CE, Stevenson FK, Scott ML, Sutherland J, Spellerberg MB, Natvig JB, Thompson KM. Cold agglutinin activity is common among human monoclonal IgM Rh system antibodies using the V4-34 heavy chain variable gene segment. Transfusion 1997; 37: 1111-1116 and Thorpe SJ, Ball C, Fox B, Thompson KM, Thorpe R, Bristow A. Anti-D and anti-i activities are inseparable in V4-34-encoded monoclonal anti-D: the same framework 1 residues are required for both activities. Transfusion 2008; 48: 930-940). I hope this helps a little.
  7. How did you type the baby for the Fy(a) antigen, if the DAT was positive?
  8. Alloasorption. In fact, having worked in Reference Laboratories for most of my life, it was VERY unusual for the patient either to have NOT have a transfusion within the previous three months - meaning that they were not a candidate for auto-adsorptions - or their haematocrit is so low that there are too few autologous red cells to perform an auto-adsorption in the first place (usually because they were sent to us because they needed a transfusion in the first place!).
  9. If the titre is on a new patient, we (UK) would a NIBSC (National Institute for Biological Standards and Control) anti-D. If it is a second or subsequent sample, we would titrate the stored (and frozen) previous sample, in parallel with the new sample. If there was found to be a difference in titre, we would again use a NIBSC anti-D in parallel.
  10. I like explanation one very much exlimey. Very many of the examples of anti-Vel I have encountered (and I have seen many, as I was working at the BGRL in London in the mid to late 1970's when Dr Bertil Cedegren was studying the percentage of Vel Negative donors in the Swedish population) had a high concentration of IgM, and a low concentration of IgG.
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