CXCL13 and infection: A significant transient increase in serum CXCL13 levels was noted at 3 days post 2nd, 3rd, and 4th IN infections (4.4- and 5.5-fold increase, respectively); however, at 3 weeks post 2nd and 3rd infection, CXCL13 levels had dropped to levels comparable to those in the naive sera.