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Related Concept Videos

Complement System01:27

Complement System

The complement system is a group of approximately 20 plasma proteins that strengthen the body's defenses against infections through opsonization, inflammation, and cell lysis. Opsonization involves coating pathogens with complement proteins, making them more recognizable and facilitating phagocyte engulfment. Certain complement proteins induce inflammation that attracts immune cells to the site of infection. Cell lysis involves the destruction of pathogens through the formation of a membrane...
Coronavirus01:29

Coronavirus

Coronaviruses, including the severe acute respiratory syndrome coronavirus (SARS-CoV), are enveloped viruses characterized by their single-stranded, positive-sense RNA genome and helical nucleocapsid structure. The hallmark of these viruses is their club-shaped spike (S) glycoproteins that protrude from the viral envelope, facilitating attachment to host cells. Typically, coronaviruses infect the upper respiratory tract, often causing mild or asymptomatic disease. However, certain strains like...
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...
Hypersensitivity Reactions: Immune-Complex Reactions01:19

Hypersensitivity Reactions: Immune-Complex Reactions

Type III hypersensitivity reactions occur when antigen–antibody complexes form and activate the complement system. Normally, these complexes help the clearance of antigens by phagocytes and red blood cells. However, when large numbers of immune complexes are present, they can deposit in tissues—particularly in the walls of blood vessels—leading to inflammation and tissue injury. These deposits trigger complement activation and neutrophil recruitment, resulting in serum sickness, a systemic...
Pneumonia II: Pathophysiology01:29

Pneumonia II: Pathophysiology

The pathophysiology of pneumonia involves the following steps:
Acute Coronary Syndrome II: Pathophysiology and Clinical Manifestations01:19

Acute Coronary Syndrome II: Pathophysiology and Clinical Manifestations

The pathophysiology of Acute Coronary Syndrome [ACD] involves several key processes:The main underlying cause of ACD is atherosclerosis, a chronic inflammatory disease characterized by the buildup of lipid-laden plaques within the coronary arteries.As the atherosclerotic plaque grows in the coronary artery, it may become unstable due to the formation of a lipid-rich core and a thin fibrous cap. Inflammatory cells within the plaque, such as macrophages, secrete enzymes that degrade the...

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Related Experiment Video

Updated: May 31, 2026

Whole Blood Assay with Dual Co-Stimulation for Antigen-Specific Analysis of Host Immunity to Fungal and Viral Pathogens
06:03

Whole Blood Assay with Dual Co-Stimulation for Antigen-Specific Analysis of Host Immunity to Fungal and Viral Pathogens

Published on: September 20, 2024

Complement activation in patients with post-acute sequelae after SARS-CoV-2 infection.

Madlene Holmqvist1,2, Dick J Sjöström3, Katherine Carlson1

  • 1Division of Infection Medicine, Department of Clinical Sciences, Lund University, Lund, Sweden.

Frontiers in Immunology
|May 29, 2026
PubMed
Summary

Researchers investigated complement system activation in patients with post-acute sequelae of SARS-CoV-2 (PASC). This study found no convincing evidence of complement system dysregulation in PASC patients, regardless of initial COVID-19 severity.

Keywords:
COVID-19PACSPASCSARS-CoV-2complement activationlong COVIDpost COVID syndrome

More Related Videos

Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells
06:29

Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells

Published on: January 29, 2014

Related Experiment Videos

Last Updated: May 31, 2026

Whole Blood Assay with Dual Co-Stimulation for Antigen-Specific Analysis of Host Immunity to Fungal and Viral Pathogens
06:03

Whole Blood Assay with Dual Co-Stimulation for Antigen-Specific Analysis of Host Immunity to Fungal and Viral Pathogens

Published on: September 20, 2024

Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells
06:29

Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells

Published on: January 29, 2014

Area of Science:

  • Immunology
  • Infectious Diseases
  • Post-COVID Conditions

Background:

  • Post-acute sequelae of SARS-CoV-2 (PASC) present diverse, long-lasting symptoms after infection.
  • Dysregulation of the complement system is a proposed mechanism for PASC development.

Purpose of the Study:

  • To analyze complement activation markers in patients with PASC.
  • To determine if complement system activation correlates with PASC severity or initial COVID-19 infection status.

Main Methods:

  • Measured complement activation markers (C3bc, C3bBbP, TCC) in PASC patients and controls.
  • Compared marker levels between PASC patients (mild vs. severe initial infection) and recovered controls.

Main Results:

  • No significant differences in complement activation markers were found between PASC patients and controls.
  • A trend towards more severe PASC was observed in patients with mild initial SARS-CoV-2 infection, but this did not correlate with complement activation.

Conclusions:

  • This study did not find convincing evidence for complement system activation in PASC.
  • The role of complement dysregulation in the pathophysiology of PASC remains uncertain based on these findings.