Immunoreactive S100 proteins of blood immunocytes and brain cells

Brain S100, an acidic protein with Ca2+-binding and neurotrophic properties, may be involved in the genesis of neurodegenerative diseases. Based on sharing of common antigens between the immune and nervous systems, we performed a comparative analysis of S100 in blood immunocytes (lymphocytes and monocytes) and brain cells. By using polyclonal antibodies to S100, an immunoreactive S100 was detected in human blood immunocytes and U373 human astrocytoma cells. The U373 cells contained a much higher level of S100 as compared to immunocytes, both cell types being compared at 1 X 10(6) cell concentration. Through protein-immunoblotting, the immunocyte antigen was compared with pure S100 of bovine brain (authentic sample) and S100 of U373 cells and brain cells (human and mouse brain). The monomeric form of immunocyte-derived S100 was a low molecular mass (12-14kDa) protein, but slightly larger than authentic S100 (10.5 kDa) The S100 of U373 cells and brain cells was mainly a polymer (60-100 kDa), although the brain cells also showed a low molecular mass (10.5 kDa) band that corresponded to authentic S100. The molecular mass differences suggest that peripheral blood immunocytes contain an immunoreactive S100 that differs in size but is antigenically related to brain S100 family.