Inactivation of TNF production by both B and T cells results in impaired humoral response to T-cell–dependent antigen. (A) Mice were immunized i.p. with 10⁸ SRBCs. Sera were collected on day 21, and anti-SRBC response was measured by ELISA. Symbols indicate individual mice. Mean values are indicated. IgG response is reduced both in B-TNF and T-TNF KO mice, however not as severe as in T,B-TNF and TNF KO mice. Symbols indicate individual mice. One of 3 experiments with similar results is shown (n = 5-8 mice per group). (B) Mice were immunized i.f.p. with 10⁸ SRBCs and anti-SRBC IgG titers were analyzed on day 21. SplX-WT mice were splenectomized 10 days before immunization. LTα KO mice are included as control. Average is indicated. Symbols indicate individual mice. One of 2 independent experiments with similar results is shown (n = 5-8 mice per group); *P < .05, **P < .01, NS, not significant. (C) Administration of TNF blocker inhibits humoral immune response to T-cell–dependent antigen. Mice were immunized i.p. with 10⁸ SRBCs and specific anti-IgG response was measured at day 21. Etanercept (30 mg/kg) was injected twice per week starting from day −6. One of 2 independent experiments with similar results is shown. Each symbol represent individual mouse. Average is indicated; *P < .05.