Flow cytometric assay detecting cytotoxicity against human endogenous retrovirus antigens expressed on cultured multiple sclerosis cells

Abstract

Damage of target cells by cytotoxicity, either mediated by specific lymphocytes or via antibody-dependent reactions, may play a decisive role in causing the central nervous system (CNS) lesions seen in multiple sclerosis (MS). Relevant epitopes, antibodies towards these epitopes and a reliable assay are all mandatory parts in detection and evaluation of the pertinence of such cytotoxicity reactions. We have adapted a flow cytometry assay detecting CD107a expression on the surface of cytotoxic effector cells to be applicable for analyses of the effect on target cells from MS patients expressing increased amounts of human endogenous retrovirus antigens. MS patients also have increased antibody levels to these antigens. The target cells are spontaneously growing peripheral blood mononuclear cells (PBMCs) of B cell lineage, expressing human endogenous retrovirus HERV epitopes on their surface. Polyclonal antibodies against defined peptides in the Env- and Gag-regions of the HERVs were raised in rabbits and used in antibody-dependent cell-mediated cytotoxicity (ADCC) -assays. Rituximab® (Roche), a chimeric monoclonal antibody against CD20 expressed primarily on B cells, was used as control antibody. Without antibodies this system is suitable for analyses of natural killer cell activity. In optimization of the assay we have used effector lymphocytes from healthy donors. The most effective effector cells are CD56(+) cells. CD8(+) T cells also express CD107a in ADCC. Using the adapted assay, we demonstrate significant ADCC activity to target cells expressing HERV epitopes, and additionally a low level of NK activity.