What's the difference between naive and memory B cells?
The main difference is that memory B cells start an immune reaction much more effective and faster than naive B cells. The reaction is also specific towards the antigen.

The memory B cell has a specific membrane receptor for an antigen. It produces specific antibodies only when exposed to the antigen.

References:


Tangye SG, Avery DT, Deenick EK, Hodgkin PD. Intrinsic differences in the proliferation of naive and memory human B cells as a mechanism for enhanced secondary immune responses. J. Immunol. 2003 Jan 15;170(2):686-94. PubMed PMID: 12517929. 
Wikipedia contributors, "B cell," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=B_cell&amp;oldid=612990219 (accessed June 26, 2014).