HLA-F is a surface marker on activated lymphocytes

Abstract

Of the three nonclassical class I antigens expressed in humans, HLA-F has been least characterized with regard to expression or function. In this study, we examined HLA-F expression focusing on lymphoid cells, where our previous work with homologous cell lines had demonstrated surface HLA-F expression. HLA-F protein expression was observed by Western blot analysis in all resting lymphocytes, including B cells, T cells, NK cells, and monocytes, all of which lacked surface expression in the resting state. Upon activation, using a variety of methods to activate different lymphocyte subpopulations, all cell types that expressed HLA-F intracellularly showed an induction of surface HLA-F protein. An examination of peripheral blood from individuals genetically deficient for TAP and tapasin expression demonstrated the same activation expression profiles for HLA-F, but with altered kinetics post-activation. Further analysis of CD4+CD25+ Treg showed that HLA-F was not upregulated on the major fraction of these cells when they were activated, whereas CD4 +CD25- T cells showed strong expression of surface HLA-F when activated under identical conditions. These findings are discussed with regard to possible functions for HLA-F and its potential clinical use as a marker of an activated immune response. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.