B-Cell Mediated Humoral Responses Are Impaired in Sepsis Survivors

Abstract

Sepsis survivors exhibit a sustained compromise in innate immunity, and high mortality rates due to increased vulnerability to infections. Previously we demonstrated in a cecal ligation and puncture (CLP) model, that sepsis survivors had a reduced TNFα response to LPS-challenge in vivo, which is accompanied by an increase in CD4+ChAT+ T cells. These data together with clinical observations of low endogenous levels of IgG in sepsis survivors led us to hypothesize that T-cell dependent (T-D) B cell responses might also be altered after CLP. In order to assess alterations in the adaptive humoral response in sepsis survivors, we immunized C57BL/6J sham surgery and CLP mice with a single intraperitoneal (I.P.) injection of NP (29)-KLH (T-D antigen) in alum 4 weeks post-CLP (or sham surgery). We observed sepsis survivors showed reduced serum NP-specific IgG and IgG1 antibodies compared to sham controls. Furthermore, to confirm whether this reduced immune response is mediated through a T-D or T cell-independent (T-I) type II mechanism, we used other carrier molecules CGG (T-D) and Ficoll (T-I), respectively. To evaluate time dependent kinetics, we immunized mice with single I.P. injection of either NP (20)-CGG or NP (55)-Ficoll. We analyzed both low-affinity and high-affinity anti-NP antibodies through NP (23)- and NP (7)- BSA ELISAs, respectively. We found a significant reduction in anti-NP IgG and IgG1 antibodies in CLP mice post-NP-CGG immunization (p<0.01 and p<0.001, respectively) while the response was not diminished after NP-Ficoll immunization at day 7; suggesting that compromised antibody response is mediated through a T-cell dependent pathway. Flow cytometry data also revealed that the splenic frequency of NP-specific CD138+ intracellular IgG1 plasma cells was decreased in CLP mice immunized with NP-CGG as compared to sham mice at day 7, 14 and 21 (p<0.001, p<0.05 and p<0.05, respectively). Since follicular dendritic cells (FDCs) play a key role in B-cell activation and affinity maturation of antibodies, we performed immunofluorescence staining of FDCs in spleens from sham surgery and CLP mice. Interestingly, we found a decreased number of FDC clusters in CLP mice compared to sham controls. In summary, our study is clinically relevant as it may explain the hypogammaglobulinemia seen in sepsis surviving patients. DisclosuresNo relevant conflicts of interest to declare.