Heat‐inactivation of human serum destroys c1 inhibitor, pro‐motes immune complex formation, and improves human t cell function

Abstract

Heat‐inactivation of sera is used to reduce possible disturbing effects of complement factors in cell‐culture experiments, but it is controversially discussed whether this procedure is appro-priate or could be neglected. Here, we report a strong impact of heat‐inactivation of human sera on the activation and effector functions of human CD4+ T cells. While T cells cultured with native sera were characterized by a higher proliferation rate and higher expression of CD28, heat‐inactivated sera shaped T cells towards on‐blast formation, higher cytokine secretion (interferon γ, tumor necrosis factor, and interleukin‐17), stronger CD69 and PD‐1 expression, and increased metabolic ac-tivity. Heat‐inactivated sera contained reduced amounts of complement factors and regulators like C1 inhibitor, but increased concentrations of circulating immune complexes. Substitution of C1 in-hibitor reduced the beneficial effect of heat‐inactivation in terms of cytokine release, whereas sur-face‐molecule expression was affected by the addition of complex forming anti‐C1q antibody. Our data clearly demonstrate a beneficial effect of heat‐inactivation of human sera for T cell experiments but indicate that beside complement regulators and immune complexes other components might be relevant. Beyond that, this study further underpins the strong impact of the complement system on T cell function.