Related Experiment Video

Updated: May 28, 2026

Modeling Dysplastic and Functional Lung Alveolar Repair after Influenza Infection
07:45

Modeling Dysplastic and Functional Lung Alveolar Repair after Influenza Infection

Published on: September 19, 2025

Potential role for alternatively activated macrophages in the secondary bacterial infection during recovery from

Wilbur H Chen1, Franklin R Toapanta, Kari Ann Shirey

  • 1Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, MD 21201, USA. wchen@medicine.umaryland.edu

Immunology Letters
|November 1, 2011
PubMed
Abstract

Insights

Influenza infection impairs immune defenses, making mice susceptible to secondary bacterial pneumonia. Pulmonary alternatively activated macrophages (AAM) induced by influenza may drive this increased susceptibility.

Area of Science:

  • Immunology
  • Infectious Diseases
  • Pulmonary Medicine

Background:

  • Secondary bacterial infections frequently complicate influenza virus infections.
  • Impaired innate immune defenses post-influenza contribute to heightened susceptibility to bacterial pathogens.
  • Pulmonary alternatively activated macrophages (AAM) are implicated in the hypersusceptibility to secondary bacterial pneumonia.

Purpose of the Study:

  • To investigate the role of pulmonary alternatively activated macrophages (AAM) in the increased susceptibility to secondary bacterial pneumonia following influenza infection.
  • To elucidate the mechanisms of immune regulation during recovery from influenza.

Main Methods:

  • C57BL6 mice were infected with sublethal doses of influenza A virus (PR8) or saline.
  • Following recovery, mice were re-challenged with Streptococcus pneumoniae.
  • Gene expression, flow cytometry, and cytokine responses were analyzed.

Main Results:

  • Mice recovered from influenza (PR8) exhibited a 100-fold increased susceptibility to a lethal Streptococcus pneumoniae challenge compared to naive mice.
  • Pulmonary AAM markers (Arginase-1, FIZZ1, YM1) and associated cytokines (IL-4, IL-13) were upregulated post-influenza.
  • Alveolar macrophages displayed AAM phenotype markers (MGL-1, MHCII) after PR8 infection.
  • Influenza recovery was linked to blunted cytokine responses to TLR ligands.

Conclusions:

  • Pulmonary alternatively activated macrophages (AAM) are induced during influenza infection.
  • These AAM may play a critical role in mediating hypersusceptibility to secondary bacterial pneumonia after influenza.
  • Further research into influenza-induced immune dysregulation is warranted.

More Related Videos

Isolation and In Vitro Culture of Murine and Human Alveolar Macrophages09:09

Isolation and In Vitro Culture of Murine and Human Alveolar Macrophages

Published on: April 20, 2018

A Precise Pathogen Delivery and Recovery System for Murine Models of Secondary Bacterial Pneumonia13:45

A Precise Pathogen Delivery and Recovery System for Murine Models of Secondary Bacterial Pneumonia

Published on: September 21, 2019

Related Concept Videos

Defense Against Bacterial Pathogens01:31

Defense Against Bacterial Pathogens

The human immune system is a complex network of cells, tissues, and organs that work together to defend the body against bacterial infections. It consists of various immune cells, each playing a specific role in the defense mechanism.
Phagocytes
Phagocytes are the frontline soldiers of the immune system. They include neutrophils and macrophages. Neutrophils are the most abundant type of white blood cell and are quickly mobilized to the site of infection. Macrophages are larger cells that patrol...
Immune Surveillance by NK Cells and Phagocytes01:25

Immune Surveillance by NK Cells and Phagocytes

Immune surveillance is an integral part of the innate immune system, involving the continuous monitoring of peripheral tissues to detect and respond to pathogens, infected cells, or cancerous cells. This surveillance is conducted primarily by natural killer (NK) cells and phagocytes, which employ distinct but complementary mechanisms to identify and eliminate threats.
Natural Killer Cells: The Fast Responders
NK cells are large granular lymphocytes found in the blood and lymphatic system. These...
Cell-mediated Immune Responses01:40

Cell-mediated Immune Responses

Overview
Immune Response Against Viral Pathogens01:29

Immune Response Against Viral Pathogens

The immune system's response to viral infections is a complex and coordinated process involving natural killer (NK) cells, T cell-mediated responses, and antibody-mediated responses.
NK Cells
NK cells are a crucial part of our innate immune system, acting as the first line of defense against viral infections. These cells can recognize and kill infected cells without prior exposure to the virus, effectively slowing down the spread of infection. Additionally, NK cells produce proinflammatory...
Chronic Inflammation: Introduction01:12

Chronic Inflammation: Introduction

Chronic inflammation is a prolonged, dysregulated immune response that persists for weeks to years when the inciting stimulus is difficult to eradicate or when self‑antigens drive ongoing reactivity. Morphologically, it is defined by mononuclear cell infiltration, progressive tissue destruction, and concurrent attempts at healing via angiogenesis and fibrosis. Compared with acute inflammation, edema is less prominent while cellular infiltration predominates; triggers include persistent...
Acute Inflammation II: Cellular Phase01:26

Acute Inflammation II: Cellular Phase

The cellular phase of acute inflammation is a tightly orchestrated sequence of events that recruits leukocytes, primarily neutrophils, to sites of tissue injury or infection. Following the initial vascular changes, this phase ensures effective immune cell migration, activation, and function at the affected site to eliminate pathogens and initiate tissue repair.Leukocyte Recruitment CascadeLeukocyte recruitment happens in four steps: margination, adhesion, transmigration, and chemotaxis. Reduced...