The disclosed technology introduces nanobodies designed to modulate B cell activation with unprecedented precision. Currently in the proof-of-concept stage, this innovative approach selectively targets resting B cells, suppressing activation induced by anti-BCR antibody fragments without depleting B cells entirely. Unlike existing therapies that rely on wholesale B cell elimination and often result in significant toxicity, this invention offers a novel therapeutic strategy that finely tunes B cell sensitivity, paving the way for safer and more targeted treatments in autoimmune diseases, oncology, and other conditions involving B cell dysfunction.