# Immune activation of primary human macrophages is suppressed by the coordinated action of Yersinia effectors

## TL;DR

This study shows how Yersinia bacteria use multiple effectors to suppress immune responses in human macrophages through coordinated mechanisms.

## Contribution

The study reveals synergistic, antagonistic, and individual roles of Yersinia effectors in human macrophages using primary cells.

## Key findings

- YopP suppresses gene expression changes in macrophages induced by bacterial stimuli.
- YopP and YopQ together reduce inflammasome formation, but not other combinations.
- YopH alone blocks calcium transients in infected macrophages.

## Abstract

To suppress the host immune response, numerous bacterial pathogens utilize a type 3 secretion system (T3SS) that injects effector proteins into host target cells. We investigated the T3SS effectors of Yersinia enterocolitica (Yops) for their individual and combined effects on gene expression, inflammasome formation, and calcium signaling in primary human macrophages. YopP efficiently suppressed the upregulation and downregulation of thousands of macrophage genes induced by the bacteria’s inflammatory stimuli. This was accompanied by parallel changes in histone 3-serine 10 phosphorylation, which could represent an overarching regulatory mechanism of rapid gene expression in macrophage inflammatory response. Surprisingly, YopM and YopQ counteracted selected YopP effects on gene expression, for example, of cytokine pathways. A combination of YopP and YopQ, but not other combinations of Yops or any single Yop, reduced inflammasome formation. YopH alone blocked calcium transients in infected macrophages. We propose that the T3SS effectors of Yersinia antagonistically, synergistically, or individually subdue major immune pathways of human macrophages to jointly suppress macrophage activation.

Macrophages are one of the key target cells of pathogenic Yersinia, where central immune response pathways, such as phagocytosis, gene expression, and inflammasome assembly, are suppressed by secreted bacterial effectors (Yops) in a highly coordinated fashion. Most studies analyzing cooperation between Yop proteins have utilized cell lines and mouse-derived macrophages, which strongly differ from human macrophages. This study employed primary human macrophages and analyzed cooperation between different Yersinia enterocolitica effector proteins on gene expression, histone phosphorylation, calcium signaling, and inflammasome assembly. We reveal synergistic, antagonistic, and individual roles of different Yersinia effector proteins. This work highlights how highly coordinated activities of a limited set of effectors can efficiently disarm macrophage immune responses and lead to a successful infection.