1. HLAMatchmaker-Based Analysis of MICA Antibody Reactivity Patterns Rene J. Duquesnoy 1, Justin W. Mostecki 2, Jayasree Hariharan 2, Kristi Colacioppo 2, Bryan Ray 2 and Ivan Balazs 2 1 University of Pittsburgh Medical Center and 2 Tepnel Lifecodes Corporation Introduction HLAMatchmaker is a computer algorithm that determines HLA compatibility at the structural level. Donor-recipient histocompatibility is assessed with polymorphic amino acid configurations that represent structurally defined elements of HLA epitopes. The term “eplet” represents an epitope defined by a polymorphic surface residue and other residues within a radius of 3.0-3.5 Ångstroms. Structurally based HLA matching reduces humoral allosensitization and correlates with good transplant outcome. Moreover, HLAMatchmaker is useful in the antibody analysis of sera from highly sensitized patients. Recent studies have suggested a clinical significance of anti-MICA antibodies in transplantation. We have developed an eplet-based version HLAMatchmaker to assess the epitope specificity of anti-MICA antibodies. The amino acid sequences of the MICA alleles contain multiple polymorphic positions that likely contribute to the epitope repertoire of MICA. Molecular viewing of two published 3D structures of MICA (PDB codes IB35 and 1HYR downloaded from the NCBI website (http://www.ncbi.nlm.nih.gov/Structure) has identified 30 polymorphic positions on 53 MICA alleles. Figure1 shows four views of the polymorphic residues on MICA. Table 1 shows the locations of polymorphic residues and the residue positions used to determine MICA eplets. Table 2 shows MICA alleles with the more common eplets.http://www.ncbi.nlm.nih.gov/Structure HLAMatchmaker Analysis of MICA Antibodies: Four Examples 1.This patient typed as A*008, *010 and had received a kidney transplant from a sister who was mismatched for A*012 which had 10 mismatched eplets. Although the serum showed weak anti- MICA reactivity with this small panel it became apparent that the antibodies are specific for 24TC. 24TC containing antigens are shown in black. 2.This highly reactive serum was from a patient who typed as A*012. In this 20 antigen panel only one non-self antigen A*043 was negative. All 18 reactive antigens shared the 156H eplet and are shaded in black. 3.No MICA typing information was available. This serum reacted only with 14G positive antigens shown in black. The “acceptable” and “unacceptable “ alleles are listed. 4. No MICA typing information was available. Although this serum reacted with all 14W positive antigens (shown by black and hatched bars) you will note that there was strong reactivity with the antigens that shared 24AY, 129V, 173EE, and 206S2 which are shaded in black. It seems likely that the antibody specificity is against 14W plus one or more of these eplets. Absorption/elution analysis with informative alleles may provide further insight. Conclusions The HLAMatchmaker program to analyze MICA antibodies can be downloaded from the website http://www.HLAMatchmaker.net which has also other programs and articles about structurally based histocompatibility. Please contact Duquesnoyr@upmc.edu if you have any questions or comments. http://www.HLAMatchmaker.netDuquesnoyr@upmc.edu This study was supported by NIH grant AI-55933 Figure 1 Four views of polymorphic residues on MICA Table 1 Location and Surface Expression of Polymorphic Positions on MICA Molecules Table 2 More Common Eplets on MICA Alleles Example 1 Example 2 Example 4 Example 3