Quantitation of T-macrophage binding avidity with and without antigen using a novel centrifugation assay.

The T cell-macrophage interaction, necessary for T cell activation, has nonspecific and specific components. Nonspecific T-macrophage interactions are mediated by surface glycoproteins such as LFA 1, 2 and 3, while specific interactions are mediated by the T3-Ti complex on the T cell and antigen plus Ia molecules on the macrophage. To determine the relative contributions of specific antigen to the total avidity of T-macrophage binding we adapted a novel assay capable of providing quantitative estimations of the avidity of cell-cell interactions. Using this assay we determined the avidity of a cloned CD4+ antigen specific T cell line for autologous macrophages with and without antigen. The presence of specific antigen increased binding avidity by approximately 25%. This assay should prove useful in further characterizing the avidity of T-macrophage interactions.