Complement activation

Definition

Complement activation is a crucial immune response involving a series of proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens from an organism. This process plays a vital role in the innate and adaptive immune systems, contributing to inflammation, opsonization, and cell lysis, especially during parasitic infections. Understanding how complement activation interacts with parasites can shed light on their pathogenesis and the host's immune response.

5 Must Know Facts For Your Next Test

1. Complement activation can occur via three pathways: classical, alternative, and lectin pathways, each triggered by different stimuli.
2. During parasitic infections, complement proteins can help target parasites for destruction through opsonization, enhancing phagocytosis.
3. Some parasites have evolved mechanisms to evade complement activation, allowing them to persist in the host and cause disease.
4. Anaphylatoxins produced during complement activation can induce inflammation, which may lead to tissue damage if uncontrolled.
5. The balance between complement activation and regulation is critical; excessive activation can lead to autoimmune diseases or tissue damage.

Review Questions

• How does complement activation enhance the immune response against parasitic infections?
  • Complement activation enhances the immune response against parasitic infections by promoting opsonization, where complement proteins coat the surface of parasites. This tagging makes it easier for phagocytic cells to recognize and engulf the parasites. Additionally, the inflammatory mediators generated during this process help recruit more immune cells to the infection site, facilitating a robust immune response that targets the invading parasites.
• What are some strategies employed by parasites to evade the effects of complement activation?
  • Parasites have developed various strategies to evade the effects of complement activation. Some produce surface molecules that bind complement proteins or inhibit their function, preventing opsonization. Others may alter their surface structures to avoid recognition or trigger regulatory pathways that suppress the complement response. These adaptations allow parasites to survive longer in the host and contribute to chronic infections.
• Evaluate the role of anaphylatoxins in complement activation and their implications for disease pathogenesis in parasitic infections.
  • Anaphylatoxins play a significant role in complement activation by promoting inflammation and recruiting immune cells. In parasitic infections, the release of anaphylatoxins can enhance the inflammatory response, which may help in controlling parasite load. However, excessive levels can lead to tissue damage and exacerbate disease symptoms. Thus, while anaphylatoxins are essential for an effective immune response, their uncontrolled activity can contribute to pathology in hosts infected with certain parasites.

Related terms

Opsonization:

The process by which pathogens are marked for destruction by immune cells, enhancing their recognition and uptake.

Inflammation: A biological response to harmful stimuli, such as pathogens or tissue injury, characterized by redness, heat, swelling, and pain.

Anaphylatoxins: Small peptide fragments released during complement activation that promote inflammation and recruit immune cells to sites of infection.