High Mobility Group Box 1-Protein expression in canine haematopoietic cells and influence on canine peripheral blood mononuclear cell proliferative activity

High Mobility Group Box 1-Protein (HMGB1) is a nuclear chromosomal protein occurring ubiquitary in mammalian tissues. HMGB1 demonstrates cytokine function and induces inflammation when actively released by haematopoietic cells or passively released during cell necrosis.This study aimed at the determination of HMGB1 expression in different cell types and at the evaluation of the role of HMGB1 in PBMC proliferation. Therefore we investigated the HMGB1 mRNA expression level in different canine haematopoietic cell types and the influence of exogenous rhHMGB1 on canine PBMC proliferation.Differentiated haematopoietic blood cells showed lower relative HMGB1 expression levels compared to CD34+ haematopoietic stem cells. Relative HMGB1 expression seemed also to decrease during differentiation of CD34+ stem cells into dendritic cells. Furthermore, peripheral blood CD14+ monocytes and granulocytes showed a lower relative HMGB1 expression in comparison to CD3+ T-lymphocytes. When exogenous rhHMGB1 at low concentrations was added to single PBMC cultures an increase of proliferation was obvious. However, in higher concentrations HMGB1 lost its stimulative effect.In conclusion, HMGB1 is broadly expressed in canine haematopoietic cells with highest levels in haematopoietic stem cells. HMGB1 induced directly PBMC proliferation.