# Increased peritoneal B1-like cells during acute phase of human septic peritonitis

## TL;DR

This study finds that septic peritonitis increases peritoneal B1-like cells, which correlate with disease severity in both humans and mice.

## Contribution

The study identifies B1-like lymphocytes as a novel immune marker specifically linked to septic peritonitis severity.

## Key findings

- Myeloid expansion and lymphocyte loss occur in all abdominal surgery patients, not just septic ones.
- B1-like cells increase in septic peritoneal fluid and correlate with clinical severity scores.
- In mice, sepsis depletes B1a cells but maintains B1b cells in the peritoneum.

## Abstract

Sepsis is a life-threatening condition caused by dysregulated host responses to infection. Myeloid cell accumulation and lymphocyte decline are widely recognized phenomena in septic patients. However, the fate of specific immune cells remains unclear. Here, we report the results of a human explorative study of patients with septic peritonitis and patients undergoing abdominal surgery without sepsis. We analyzed pairwise peritoneal fluid and peripheral blood taken 24 h after surgery to characterize immediate immune cell changes. Our results show that myeloid cell expansion and lymphocyte loss occur in all patients undergoing open abdominal surgery, indicating that these changes are not specific to sepsis. However, B1-like lymphocytes were specifically increased in the peritoneal fluid of septic patients, correlating positively with sequential organ failure assessment (SOFA) and acute physiology and chronic health evaluation II (APACHE-II) clinical severity scores. In support of this notion, we identified an accumulation of peritoneal B1b lymphocytes in septic mice.

•Abdominal surgery induces severe immune cell changes independent of sepsis•Increased CD5+ B1-like cell numbers in peritoneal fluids are indicative of sepsis•Clinical severity correlates with B1-like cell frequencies in humans and mice•Murine B1a cells are depleted and B1b cells are maintained during sepsis

Abdominal surgery induces severe immune cell changes independent of sepsis

Increased CD5+ B1-like cell numbers in peritoneal fluids are indicative of sepsis

Clinical severity correlates with B1-like cell frequencies in humans and mice

Murine B1a cells are depleted and B1b cells are maintained during sepsis

Biological sciences; Immune response; Immunology