TNFSF13B and systemic lupus erythematosus: Interestingly, blocking the activity of B cell Activation Factor of the TNF Family (BAFF) with biologics, including the recently FDA-approved recombinant monoclonal antibody Belimumab (Jefferson and Liscinsky, 2011; Sanz, 2011), effectively reduces numbers of transitional and mature-naïve B cells while increasing memory-phenotype B cells early after treatment in SLE and RA (Dall’Era et al., 2007; Tak et al., 2008; Wallace et al., 2009; Jacobi et al., 2010a).