**1. The acute-phase nature of an enigmatic amyloid precursor in early experiments**

apposition toward the central liver vein (darker areas) until most of the liver is transformed into amyloid in a fatal amyloidosis. This behavior requires a consistent, steady and very fast transformation of an assumed precursor to amyloid by entering the liver capillaries. The amyloid is deposited under pressure and visible as the rough liver surface (at the top), which is

The Invariant Peptide Clusters of Serum Amyloid A Are Humoral Checkpoints for Vital Innate Functions…

http://dx.doi.org/10.5772/intechopen.91983

71

When the assumed precursor is present in blood, as suggested by morphologic evidence, it should cross the anastomosis between artificial Siamese twins (parabiosis) with one partner induced to develop amyloidosis through septic conditions. However, this transmission does not always occur. The septic partner developed amyloid in 92.5% of pairs and the untreated partner in only 13.4%, and the latter was statistically not different to that seen in control pairs without any treatment [4]. The failure of crossing the anastomosis was excluded by 51Cr-tagged erythrocytes [5]. Since the anastomosis was fully permeable, this type of parabiotic barrier was not an absolute one but a relative one caused by a short half-life of the agent that was removed from the bloodstream before it could cross the permeable anastomosis. The results of quantitation of the blood flow by 51Cr erythrocytes, including a mathematical model of the exchange rate, shows that half of the blood was exchanged between the partners in 22.3 min. Therefore, a short halflife far below 22.3 min indicates a protein with a rapid clearance in minutes or even seconds, a property that is addressed today as an *acute-phase nature*, but still enigmatic precursor [5].

The half-life of SAA1 and SAA2 in plasma of normal mice was reported for SAA-HDL as a T1/2 of 75–80 min and both isotypes were similar. However, when trace amounts of SAA were given, they were rapidly cleared [6]. Another report measured the clearance of the complex SAA-HDL for SAA1 T1/2 of 75 min and SAA2 T1/2 of 30 min, respectively. The clearance was delayed when both isotypes were bound to high-density lipoprotein (HDL) [7]. Both reports did not measure SAA under acute-phase conditions (APC). However, the report of Hoffman and Benditt [6] found a rapid clearance with trace amounts of SAA devoid of HDL and confirmed our data that are performed under a septic acute-phase condition that was to

**2. Identification of the amyloid substance and isolation of its serum** 

Amyloids of different clinical settings (also in animals, see **Figure 1**) represent characteristic fibrils under electron microscopy [8]. Therefore, for chemical identification of the amyloid, these fibrils had to be extracted in pure form followed by chromatographic isolation of the major amyloid protein for its chemical analysis by amino acid sequence analysis. The method of isolation of the pure amyloid fibrils was pioneered by Pras et al. [9]. The first amino acid sequence of an amyloid protein was published by Glenner et al. [10], which was derived from

usually sleek.

**precursor**

**1.2. Relative parabiotic barrier**

**1.3. The clearance of SAA reported by other groups**

be observed when SAA was separated from HDL (see below).

### **1.1. Microscopic morphologic evidence**

The task of my earliest work in pathology was to find out whether there was a soluble serum precursor for amyloidosis (This spacious scientific field has been reviewed pain part recently) [1, 2]. In experimental murine amyloidosis induced by septic conditions [3], morphologically significant signs are visible in **Figure 1** showing large amounts of hepatic amyloid (white areas), now recognized as amyloid A (AA). This amyloid was first deposited at the sites where the blood stream entered from the triangle of Glisson into the liver capillaries. The entire branches of blood vessels entering the liver parenchyma (left large vessel) are decorated with amyloid and, on the other hand, the branches that allow the blood to leave the liver are devoid of amyloid (right large vessel). This implies that the amyloidogenic protein is being deposited immediately when it reaches the liver upon assumed changing conditions (still unknown) by which amyloid is deposited from a soluble precursor. With time, the deposits grow by

**Figure 1.** Photomicrograph of murine AA amyloidosis. Tissue section showing hepatic capillary amyloid deposits (white areas) induced by septic multi-microbial exposure after 25 days. The amyloid is deposited under pressure visible as the rough liver surface (at the top), which is usually sleek. Formalin-fixation, 4–6 μm paraffin section, HE-staining, magnification 24.1× [4].

apposition toward the central liver vein (darker areas) until most of the liver is transformed into amyloid in a fatal amyloidosis. This behavior requires a consistent, steady and very fast transformation of an assumed precursor to amyloid by entering the liver capillaries. The amyloid is deposited under pressure and visible as the rough liver surface (at the top), which is usually sleek.

### **1.2. Relative parabiotic barrier**

**1. The acute-phase nature of an enigmatic amyloid precursor in early** 

The task of my earliest work in pathology was to find out whether there was a soluble serum precursor for amyloidosis (This spacious scientific field has been reviewed pain part recently) [1, 2]. In experimental murine amyloidosis induced by septic conditions [3], morphologically significant signs are visible in **Figure 1** showing large amounts of hepatic amyloid (white areas), now recognized as amyloid A (AA). This amyloid was first deposited at the sites where the blood stream entered from the triangle of Glisson into the liver capillaries. The entire branches of blood vessels entering the liver parenchyma (left large vessel) are decorated with amyloid and, on the other hand, the branches that allow the blood to leave the liver are devoid of amyloid (right large vessel). This implies that the amyloidogenic protein is being deposited immediately when it reaches the liver upon assumed changing conditions (still unknown) by which amyloid is deposited from a soluble precursor. With time, the deposits grow by

**Figure 1.** Photomicrograph of murine AA amyloidosis. Tissue section showing hepatic capillary amyloid deposits (white areas) induced by septic multi-microbial exposure after 25 days. The amyloid is deposited under pressure visible as the rough liver surface (at the top), which is usually sleek. Formalin-fixation, 4–6 μm paraffin section, HE-staining,

**experiments**

70 Infectious Process and Sepsis

magnification 24.1× [4].

**1.1. Microscopic morphologic evidence**

When the assumed precursor is present in blood, as suggested by morphologic evidence, it should cross the anastomosis between artificial Siamese twins (parabiosis) with one partner induced to develop amyloidosis through septic conditions. However, this transmission does not always occur. The septic partner developed amyloid in 92.5% of pairs and the untreated partner in only 13.4%, and the latter was statistically not different to that seen in control pairs without any treatment [4]. The failure of crossing the anastomosis was excluded by 51Cr-tagged erythrocytes [5]. Since the anastomosis was fully permeable, this type of parabiotic barrier was not an absolute one but a relative one caused by a short half-life of the agent that was removed from the bloodstream before it could cross the permeable anastomosis. The results of quantitation of the blood flow by 51Cr erythrocytes, including a mathematical model of the exchange rate, shows that half of the blood was exchanged between the partners in 22.3 min. Therefore, a short halflife far below 22.3 min indicates a protein with a rapid clearance in minutes or even seconds, a property that is addressed today as an *acute-phase nature*, but still enigmatic precursor [5].

### **1.3. The clearance of SAA reported by other groups**

The half-life of SAA1 and SAA2 in plasma of normal mice was reported for SAA-HDL as a T1/2 of 75–80 min and both isotypes were similar. However, when trace amounts of SAA were given, they were rapidly cleared [6]. Another report measured the clearance of the complex SAA-HDL for SAA1 T1/2 of 75 min and SAA2 T1/2 of 30 min, respectively. The clearance was delayed when both isotypes were bound to high-density lipoprotein (HDL) [7]. Both reports did not measure SAA under acute-phase conditions (APC). However, the report of Hoffman and Benditt [6] found a rapid clearance with trace amounts of SAA devoid of HDL and confirmed our data that are performed under a septic acute-phase condition that was to be observed when SAA was separated from HDL (see below).
