CD55

Definition

CD55, also known as decay-accelerating factor (DAF), is a membrane protein that plays a crucial role in regulating the complement system by preventing the formation of the C3 convertase enzyme complex. It protects host cells from damage by inhibiting complement activation, thus maintaining homeostasis and preventing unwanted inflammation. CD55's function is essential for distinguishing between self and non-self, helping to prevent autoimmunity and ensuring that the immune response is appropriately directed.

5 Must Know Facts For Your Next Test

1. CD55 is expressed on many cell types, including red blood cells, endothelial cells, and leukocytes, providing broad protection against complement-mediated lysis.
2. The binding of CD55 to C3 convertase disrupts its activity, which reduces the production of C3b, a critical component for opsonization and amplification of the immune response.
3. Deficiencies in CD55 can lead to increased susceptibility to infections and may contribute to autoimmune diseases due to unchecked complement activation.
4. CD55 interacts with other regulatory proteins like CD46 and CD59, which together help to maintain balance within the complement system.
5. In some cancers, CD55 expression can be upregulated, aiding tumor cells in evading immune detection by preventing complement-mediated destruction.

Review Questions

• How does CD55 contribute to the regulation of the complement system?
  • CD55 regulates the complement system by inhibiting the formation and activity of C3 convertase, an enzyme complex essential for the complement cascade. By binding to C3 convertase, CD55 prevents the cleavage of C3 into C3a and C3b, which are crucial for promoting inflammation and opsonization. This regulatory function helps protect host cells from damage caused by excessive complement activation while ensuring that immune responses are appropriately directed.
• What are the consequences of CD55 deficiency in humans regarding immune responses?
  • A deficiency in CD55 can lead to increased susceptibility to infections due to uncontrolled complement activation, which may cause lysis of host cells. This lack of regulation can also trigger autoimmune responses since tissues may be mistakenly targeted by the immune system when CD55 is insufficient. Individuals with CD55 deficiency might experience a range of health issues from recurrent infections to inflammatory disorders as a result of this dysregulation.
• Evaluate the potential implications of manipulating CD55 expression in cancer therapy.
  • Manipulating CD55 expression in cancer therapy could have significant implications for improving immune responses against tumors. If CD55 is downregulated in cancer cells, it may enhance their susceptibility to complement-mediated destruction by the immune system. Conversely, upregulating CD55 could help protect tumor cells from immune attacks. Understanding these dynamics allows researchers to develop targeted therapies that either enhance or inhibit CD55 function, aiming to improve patient outcomes by either bolstering anti-tumor immunity or preventing autoimmunity.

Related terms

Complement System: A part of the immune system that enhances the ability of antibodies and phagocytic cells to clear pathogens from an organism, consisting of a series of proteins that can be activated in a cascade.

C3 Convertase:

An enzyme complex formed during the complement activation pathway that cleaves C3 into C3a and C3b, playing a key role in opsonization and inflammation.

Regulatory Proteins: Proteins such as CD55 that modulate the activity of the complement system to prevent excessive activation and protect host tissues.