Suppression of the adaptive immune response after sepsis induction.

<p>Sepsis was induced in C57BL/6 mice, and on day 7, the animals were immunized intraperitoneally with TNP-OVA/OVA in alum (n = 47). Non-septic, not immunized animals (n = 32) and non-septic immunized animals (n = 25) served as controls. The antigen-specific immune response was determined 14 days after the immunization by measuring the serum concentration of anti-OVA IgG by ELISA. (A) The relative concentrations of OVA-specific IgG antibodies in serum normalized to a standard serum are shown (arbitrary units, AU). (B) The proliferative response to restimulation with OVA was measured by thymidine incorporation <i>ex vivo</i>. (C) The proliferative response to the mitogen concanavalin A (ConA) served as control. (D) Animals that had been immunized post-sepsis were divided into two groups: severely immunosuppressed mice (n = 17) had OVA-specific IgG concentrations below 10% of control values, while mildly immunosuppressed animals (n = 30) had serum concentrations greater than or equal to 10%. (E) Numbers of OVA-specific IgG-secreting cells in the bone marrow were determined in an ELISpot assay. (F) The relative antibody affinity of TNP-specific IgG was measured as binding to slightly haptenized TNP-BSA in comparison to highly haptenized TNP-BSA in an ELISA (adapted from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192197#pone.0192197.ref034" target="_blank">34</a>]). (G-J) Blood was drawn 24 h after sepsis induction and cytokine concentrations of IL-6 (G), IL-10 (H), MCP-1 (I), and TNF (J) were quantified in the sera. Severely (n = 15) and mildly immunosuppressed (n = 29) animals are compared with non-septic, not immunized controls (n = 12). In the panels A-F means and 95% confidence intervals are shown. In the panels G-J box plots depict medians and quartiles. Group differences were tested for significance with the Kruskal-Wallis test and Dunn’s multiple comparison for selected pairs. Results were pooled from five separate experiments. *** P <0.001; ** P <0.01; * P <0.05.