Immunomodulatory effects of therapeutic preparations of human albumin

Background and Objectives  Albumin is the most abundant protein in plasma and is considered to be immunologically inert. However, we recently observed that therapeutic human albumin preparations, used as protein control in studies involving high doses of IVIg, modulated the MHC II‐restricted activation of antigen‐specific T cells. In the present work, we characterized this effect in more details. Materials and Methods  An in vitro antigen presentation assay using mouse cells was used to evaluate the effect of therapeutic human albumin preparations on the activation of ovalbumin‐specific T cells. Flow cytometry and quantitative real‐time PCR were used to monitor the expression of genes involved in this process. Results  Therapeutic human albumin preparations increased T cell activation in a dose‐dependent manner. The effect was explained by an increase in the expression of MHC II and of two other genes (CIITA and H2‐M) involved in antigen presentation by murine monocytic cells. Similarly, the expression of HLA‐DR on the surface of human monocytic cells was increased following incubation with therapeutic human albumin preparations. Conclusion  Altogether, these results reveal a possible physiological role of albumin in immunological processes, leading to an increased ability of antigen presenting cells to trigger T cell activation. This immunomodulatory effect needs to be considered, at least in studies in which albumin is used as a presumably inert control protein.