Activation of Human B Lymphocytes by Nanogram Concentrations of Anti-IgM-Dextran Conjugates.

摘要

Surface immunoglobulin (sIg) cross-linking on B lymphocytes by high concentrations of anti-Ig antibody has been used to mimic antigen-stimulated B cell activation. In order to develop a system to study sIg-medicated T cell-independent B cell activation using low concentrations of antigen that are achieved under in vivo conditions, we conjugated monoclonal anti-human IgM antibody (anti-mu) to dextran (molecular weight 2 x 10) thereby increasing its valency. This dextran conjugate (anti-mu-Dex) simulated comparable levels of thymidine incorporation and B cell size increases as were seen with unconjugated anti-mu but at 100 - to 1000 - fold lower concentrations. Anti-mu-dex also simulated increases in intracellular ionized calcium (Ca(2+(sub i)) in a higher percentage of cells, of greater magnitude and of longer duration than that stimulated by unconjugated anti-mu. Interestingly, there was no direct correlation between the increases in Ca(2+(sub i)) that were simulated by anti-mu-Dex and its ability to simulate B cell proliferation. The concentrations of anti-mu-Dex (10ug/ml) that led to the highest increase in Ca(2+(sub i)) resulted in thymidine incorporation that was no greater than that of medium control, whereas 0.01 to 0.1 mug/ml stimulated significant thymidine incorporation with 50% lower levels of stimulation of Ca(2+(sub i)). These data demonstrate that anti-mu-Dex is a potent activator of human B lymphocytes.