SUMMARY REPORT FROM THE 1ST INTERNATIONAL WORKSHOP ON SOLUBLE HLA ANTIGENS - PARIS, AUGUST 1992

The First International Workshop on Soluble HLA antigens focused on th e comparison of immunoassay procedures for quantitation of soluble HLA (sHLA) class I antigens and the selection of a sHLA class I antigen i nternational standard. Several sets of serum, plasma, and cell culture supernatant specimens were assayed blindly for levels of sHLA class I antigens by 15 participating laboratories using different immunoassay formats. The sandwich ELISA using (i) for antigen capture: an anti-HL A class I heavy chain monoclonal antibody (mAb) specific for a monomor phic epitope, and (ii) for antigen detection: an anti-beta2 microglobu lin antibody-enzyme conjugate, was the assay format of choice. There w as a high inter-laboratory correlation among the majority of laborator ies. All serum and plasma specimens from normal donors, and from a sin gle transplant patient, had detectable levels of sHLA class I antigens . Paired serum and plasma specimens had similar levels of sHLA class I antigens, although plasma sHLA antigens seemed more stable than serum sHLA antigens. sHLA-A2 and sHLA-B7 antigens were detected in all spec imens from HLA-A2 and HLA-B7 donors, respectively, using allele-specif ic ELISAs. No difference in reactivity was observed for quantitation o f native sHLA class I antigens whether the capture mAb was TP25.99 (al pha 3 domain-specific) or W6/32 (alpha 2+alpha 3-specific). However, a human-mouse chimeric sHLA class I antigen reacted weakly in assays wh ich used TP25.99 mAb. The wide variation among laboratories in their r eporting of mug/ml units pointed to the need for an inter-laboratory s tandardization based on a calibrated sHLA antigen preparation. T.sB7, an sHLA-B7 antigen derived from a cell line transfected within human b eta2 microglobulin and HLA-B7 genes, was accepted as the First sHLA cl ass I Antigen International Standard at the workshop meeting.