Cellular Internalization of Staphylococcus aureus Coated with Protein A-Bound Anti-integrin Antibodies

Binding to β₁ chain integrin receptors can result in bacterial extracellular location or bacterial internalization In cultured cells. Using monoclonal antibodies (mAbs) to coat bacteria in vitro, we have shown that receptor-ligand affinity as well as receptor density determines the fate of the bacterium. In this report, we describe techniques used to coat the Gram-positive bacteria Staphylococcus aureus with anti-integrin mAbs and their application to the study of integrin-mediated bacterial internalization. The affinity of the purified anti-integrin mAb is estimated by determination of the ED₅₀ of the mAb by using cell monolayers, and the efficiency of mAb-promoted bacterial internalization is determined by a gentamicin survival assay. The efficiency of bacterial internalization promoted by various anti-β₁ chain integrin mAbs reflects differential expression of β₁ chain integrin receptors in various cell lines studied. Analysis of β₁ chain integrin receptor expression in HEp-2 cells transfectants shows that the level of bacterial internalization is directly related to the integrin receptor density.