CD27 and influenza: To identify B-cells engaged into BCR-specific interactions with influenza HA we first tried to stain PBMCs with monoclonal antibodies against the B-cell marker CD20 and the B-cell memory marker CD27 mixed with a recombinant H1 bait (rH1), or with human serum albumin (HSA), both conjugated with the Alexa-488 fluorochrome (A488).