ELSEVIER zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Isohemagglutinins and Xenoreactive Antibodies Members of a Distinct Family of Natural Antibodies William Parker, Kari Lundberg-Swanson, Zoie E. Holzknecht, Jarama Lateef, Sara zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC A. Washburn, Steven J. Braedehoeft, and Jeffrey L. Platt ABSTRACT: Just as anti-blood group A and anti-blood group B antibodies pose a strong humoral barrier to the transplantation of allogeneic organs or blood, xenoreactive natural antibodies directed against Galal-3Gal pose a barrier to the transplantation of xenogeneic organs or blood. We tested the idea chat, although “natural” iso- hemagglutinins and xenoreactive natural antibodies rec- ognize distinct structures, they have a similar origin and function. Anti-A antibodies, anti-B antibodies, and xeno- reactive natural antibodies were present in serum at simi- lar concentrations and varied with age, gender, and the concentration of total IgM in serum in a similar manner. Anti-A antibodies, anti-B antibodies, and xenoreactive natural antibodies, unlike some elicited antibodies, had a high degree of thermal lability and bound more avidly at lower temperatures. The natural antibodies manifest re- markable homogeneity and high functional avidity for determinants on a cell surface but only a weak affinity for monovalent ligands. These findings suggest that anti-A antibodies, anti-B antibodies, and xenoreactive natural an- tibodies specific for Galoll-3Gal have a common origin and function and, given similar antigen density on target cells, provide similar humoral barriers to transplantation or transfusion and that these antibodies may be members of a common “family” of antibodies. ABBREVIATIONS BSA bovine serum albumin ELISA enzyme-linked immunosorbant assay Galal-3Gal galactobiose Ig immunoglobulin PBS SDS TBS phosphate-buffered saline sodium dodecyl sulfate Tris-buffered saline INTRODUCTION All mammalian species have in their blood “natural” antibodies which arise without a known history of sen- sitization [I). Natural antibodies appear to be a hetero- geneous group of antibodies reacting with foreign organ- isms, especially bacteria, allogenic erythrocytes, and xe- nogeneic cells 121. In binding to these surfaces, natural antibodies recognize a variety of structures including the blood groups A and B, phosphorylcholine 131, erythro- cyte band 3 141, the T antigen, and such autoantigens as the Fc domains of immunoglobulins, thyroglobulin, in- sulin, and ssDNA [S-S]. We carried out an analysis of two types of natural antibodies, xenoreactive natural antibodies and isohem- From the Deparment~ (4 Sqwy (W.P.. K. L.-S., Z.B.H.. .J, L., S. A. W.. S.J. B.. J. L. P.). Immmolo~y iJ. L. PI. and Pediatrm ,J, L.P.). Duke Univermy Medical Center. Durhn~. North Carolina. USA. Addren reprint requrts to Dr. J. L. PLatt, Department ~f~Surgery, Duke University Medical Center. Box 2605. Dwham. NC _77710. USA. Received September 7. 1995: accepted Deremher 1 I, 1995. agglutmms. Both types of antibodies mediate rejection of organ grafts in which the corresponding antigens are expressed on donor endothelium [9-11). Although re- jection mediated by xenoreactive natural antibodies and by isohemagglutinins is caused by immunoglobulin M (IgM) antibodies which activate the complement system, it has not been proven that xenoreactive natural antibod- ies and isohemagglutinins are members of a common family. Indeed, classic studies on xenoreactive natural antibodies and isohemagglutinins concluded that each of Human Immunology 45, 94-104 (1996) 019X-8859/96/$1 i.00 0 American Sociery for Hiscocompat~bd~ty and Immunogenetlrs, 1 ‘)‘)(I SSDI 0198.8859(95)002 16-2