APR in Immune System

Study Notes

The Acute Phase Response (APR)

APR is a vital component of the innate immune system.
Research on APR began in the 19th century, and its significance in veterinary medicine was recognized in the late 1980s.

Mechanism of APR

Tissue damage or impairment triggers the production and release of proinflammatory cytokines (IL-1, IL-6, TNF-α).
These cytokines activate the liver and other extrahepatic tissues to produce acute phase proteins (APP).

Acute Phase Proteins (APP)

APPs are released into the bloodstream and perform various functions, including immunomodulation and inflammation regulation.
In canines, APPs can be categorized as:
- Major APPs: proteins with negligible serum levels in normal states, but increase 10-1000 times (>25%) when stimulated.
- Moderate APPs: proteins with a 2-10 times abnormal increase (e.g., haptoglobin, fibrinogen).
- Minor APPs: proteins with a small and slow increase, followed by a delayed decrease in serum levels.
- Negative APPs: proteins inhibited by cytokine-induced stimulation, resulting in decreased serum levels (e.g., albumin).

APP Response to Infection

APPs respond to infection in a characteristic manner, as shown in Figure 1.
The classification of APPs can vary depending on the type of assay used, which affects their detectability.

Acute Phase Proteins (APPs) in Canines

APPs in canines exhibit varying baseline levels and significant variability between different APPs
The clinical importance of APPs also varies

Studied APPs in Canines

C-reactive protein (CRP) is the most widely tested APP in clinical settings
Other comprehensively studied APPs in canines include: haptoglobin, α1-acid glycoprotein (AGP), and serum amyloid A (SAA)

Function of C-Reactive Protein (CRP)

Believed to play a role in enhancing opsonization
Induces complement and cytokines
Impedes chemotaxis

CRP Production and Inflammation

Produced in response to cytokine induction
Highly sensitive to inflammatory conditions
Non-discriminate production leads to low specificity

Description

Learn about the Acute Phase Response (APR) and its role in the innate immune system, including its history, triggers, and significance in veterinary medicine. Discover the current understanding of APR, including the release of proinflammatory cytokines.