Negative Acute Phase Proteins vs. Positive

Attribute	Negative Acute Phase Proteins	Positive
Definition	Proteins whose levels decrease during acute inflammation	Proteins whose levels increase during acute inflammation
Examples	Albumin, Transthyretin	C-reactive protein, Serum amyloid A
Function	Regulate immune response, maintain homeostasis	Promote inflammation, tissue repair
Expression	Downregulated	Upregulated
Diagnostic Value	Decreased levels may indicate chronic inflammation or malnutrition	Increased levels may indicate acute inflammation or infection

Introduction

Acute phase proteins (APPs) are a group of proteins that are synthesized by the liver in response to inflammation or infection. They play a crucial role in the body's immune response and are classified into two categories: negative acute phase proteins (NAPPs) and positive acute phase proteins (PAPPs). While both types of APPs are involved in the acute phase response, they have distinct attributes and functions. In this article, we will explore the characteristics of NAPPs and PAPPs, highlighting their differences and importance in the immune system.

Negative Acute Phase Proteins

Negative acute phase proteins are characterized by a decrease in their plasma concentration during the acute phase response. This downregulation is in contrast to the upregulation observed in positive acute phase proteins. NAPPs are involved in various physiological processes, including the regulation of inflammation, tissue repair, and modulation of the immune response.

One example of a NAPP is albumin, the most abundant protein in human plasma. Albumin plays a crucial role in maintaining osmotic pressure and transporting various substances, such as hormones, fatty acids, and drugs, in the bloodstream. During inflammation or infection, the concentration of albumin decreases due to increased capillary permeability and leakage into the inflamed tissues. This decrease in albumin levels is a characteristic feature of the acute phase response.

Another NAPP is transferrin, which is responsible for iron transport in the body. Transferrin binds to iron and delivers it to cells for various metabolic processes. During inflammation, transferrin levels decrease as the body sequesters iron to limit its availability to pathogens. This reduction in transferrin concentration helps to restrict the growth of microorganisms that require iron for their survival and replication.

Additionally, NAPPs such as retinol-binding protein and thyroxine-binding globulin also exhibit decreased plasma levels during the acute phase response. These proteins are involved in the transport of retinol (vitamin A) and thyroxine (thyroid hormone), respectively. The downregulation of these proteins during inflammation or infection suggests a redirection of resources towards the immune response rather than metabolic processes.

Positive Acute Phase Proteins

Positive acute phase proteins, in contrast to NAPPs, show an increase in their plasma concentration during the acute phase response. These proteins are primarily involved in promoting inflammation, tissue repair, and combating pathogens. They play a crucial role in the immune response and contribute to the resolution of inflammation and restoration of homeostasis.

C-reactive protein (CRP) is a well-known PAPP that is widely used as a marker of inflammation. CRP levels rise rapidly in response to infection or tissue damage. It binds to microbial surfaces and activates the complement system, enhancing the immune response against pathogens. CRP also promotes phagocytosis, the process by which immune cells engulf and destroy foreign particles or microorganisms.

Another important PAPP is fibrinogen, a protein involved in blood clotting. Fibrinogen is converted into fibrin during the coagulation cascade, forming a mesh-like structure that helps in wound healing and preventing excessive bleeding. Increased fibrinogen levels during the acute phase response ensure an adequate clotting response to protect against further tissue damage.

Haptoglobin is another PAPP that binds to free hemoglobin released from damaged red blood cells. By binding to hemoglobin, haptoglobin prevents its oxidative damage and subsequent kidney filtration. This protein also has immunomodulatory effects, regulating the inflammatory response and reducing tissue damage.

Other examples of PAPPs include serum amyloid A, alpha-1 antitrypsin, and ferritin. These proteins have diverse functions, such as promoting tissue repair, inhibiting proteases, and sequestering iron, respectively. Their upregulation during the acute phase response contributes to the resolution of inflammation and restoration of homeostasis.

Conclusion

In summary, negative acute phase proteins (NAPPs) and positive acute phase proteins (PAPPs) are two distinct groups of proteins involved in the acute phase response. NAPPs exhibit a decrease in plasma concentration during inflammation or infection and are involved in regulating inflammation, tissue repair, and immune modulation. On the other hand, PAPPs show an increase in plasma concentration and play a crucial role in promoting inflammation, tissue repair, and combating pathogens. Understanding the attributes and functions of NAPPs and PAPPs is essential for unraveling the complex immune response and developing targeted therapeutic interventions for various inflammatory and infectious diseases.