Impaired IgG production in CXCR5^-/- mice. Serum TNP-specific IgG1 or IgG2a levels were determined 9 days after intraperitoneal immunization of CXCR5^-/- (□; 129SV background) and 129SV wild-type (▪) with TNP-BSA/poly I:C or 9 days after intraperitoneal immunization of CXCR5^-/- (C57BL6 background) and C57BL6 mice with TNP-BSA plus CT. (Mean + SEM; n = 3 for CT; n = 6-8 for poly I:C; ^**P < .01, ^*P < .05; unpaired 2-tailed Student t test).