Lymphocyte stimulation by protein A of Staphylococcus aureus

Protein A from Staphylococcus aureus (SpA) is known to bind to the Fc region of most mammalian IgG classes. In the present article data are presented showing that SpA is a highly efficient mitogen for human peripheral B lymphocytes, with no detectable activity for T lymphocytes. In order to achieve optimal stimulating conditions SpA should be presented to the lymphocytes on an insoluble matrix, such as the SpA-positive bacteria themselves or SpA covalently attached to Sephadex or Sepharose beads. Using such conditions SpA is equivalent with regard to stimulatory capacity for B lymphocytes as phytohemagglutinin is for the human T lymphocytes. Specificity controls proved beyond doubt that SpA and not any other contaminating product is the B cell mitogen. It is concluded that SpA as an inducer of human B lymphocyte division might serve as a highly useful assay in the clinical assessment of B lymphocyte function. It should also be a suitable tool in the fine analysis of B lymphocyte activation via the specific interactions with surface IgG molecules.