Reaction patterns of monoclonal antibodies to HLA-G in human tissues and on cell lines: a comparative study

We compared the immunohistochemical reaction patterns of HLA-G-specific antibodies 87G, 4H84, G233, 16G1, and BFL.1 on human placentas under three different preparative conditions and on cryosections of other human tissues. Human and murine cell lines, either naturally expressing or transfected with HLA-G, were analyzed for their reaction patterns by immunocytochemistry and flow cytometry. Antibodies HCA2, TP25.99, W6/32 to classical HLA class I, anti-beta(2)-m and various non-HLA-G expressing cell lines were used as controls. The binding ability of the antibodies depends on the histotechnical procedure used. 4H84 and HCA2 bind to HLA-G despite aldehyde fixation and also paraffin embedding. 87G does not bind HLA-G in studies involving fixation with aldehydes. G233 labels HLA-G in aldehyde fixed but not paraffin embedded tissues. By immunocytochemistry HLA-G2 is merely detected with antibodies 4H84 and HCA2. MAb 16G1 binds to HLA-Gsol transfected cell lines only. The HLA-G specificity of mAb BFL.1 was considered as doubtful because it failed to react with most of the HLA-G transfected cell lines. Binding of 87G to the surface of monocytes or U-937 cells stimulated with IFN-gamma and GM-CSF is an Fc-receptor mediated phenomenon.