Dear all, in view of the many enquiries like the recent one by Richard Meister about cross-reactive anti CD57 antibodies, I want to urge a cautious approach in general about antibodies raised to human cells for use in other species. Tempting though it is to simply look for cross-reactive antibodies, this approach may be very misleading. In the recent Third International Workshop on Swine Leucocyte Differentiation Antigens, a panel of 27 antibodies with previously reported cross-reactivity for pig cells was tested by the full workshop. As a result, only 10 of them could be endorsed by the workshop for use on pig cell. The results will shortly be published in a special edition of Vet. Immunol Immunopath. I can summarise the basic conclusions: The use of cross-reactive mAb has several inherent problems. The most obvious one is considerably lower affinity, with associated problems of low signal and susceptibility to titration effects. A more serious one, well documented in this study, is the different cellular expression of molecules by different species. An interesting example is the expression of CD11b on pig cells: The established anti CD11b clone TMG6-5, together with a second clone, raised to pig cells with identical specificity, showed that pig monocytes and about 50% of PMN lack this molecule, but NK cells and the remaining PMN express it; the molecular weight is identical in both pigs and humans. In addition, pigs appear to express a slightly heavier integrin chain, which shows the cellular distribution expected of human CD11b. Similar differences were found for two more antibodies (CD50 and CD11c), and a colleague reported differences for CD59. So this phenomenon is apparently quite common. So if you want to take this shortcut, you really need to be sure that the cellular distribution is the same in your species, before you can draw any meaningful conclusions. Sorry! Karin Haverson ---------------------- Dr.K Haverson, Division of Clinical Veterinary Science, University of Bristol, Langford, BS40 5DU, UK e-mail: Karin.Haverson@bristol.ac.uk Tel.: (44) 117 928 9289 FAX: (44) 117 928 9505
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