Arthropathic Properties Related to the Molecular Weight of Peptidoglycan-Polysaccharide Polymers of Streptococcal Cell Walls (1)
The covalently bound polymers of peptidoglycan and group-specific polysaccharide (PG-APS) were isolated from the cell walls of group A streptococci. Arthritis was induced in rats with a single intraperitoneal injection of an aqueous suspension of PG-APS fragments derived by sonication. The arthropathogenic activity of PG-APS to the particle size of the fragments obtained by sonic degradation.
The purified cell wall preparation consists of covalently bound polymers of peptidoglycan
(PG) and group-specific polysaccharide (APS). On the basis of rhamnose determinations with fractionated PG-APS, 22% of the recovered fragments were in the 10p fraction, 53% were in the 100p fraction, and 25% were in the 100s fraction.
Under the conditions of sonication employed, the molecular weight after 70min was approximately 500 x 10^6.
The change in particle size with sonication is a reflection of the breaking of bonds in the cross-linking peptide and in the glycan backbone of the PG. These changes, measured by the increase in free amino groups and reducing sugars, reached a plateau at about 70 min of sonication under the conditions employed.
Most of the 100p fragments of PG-APS were excluded on this gel, indicating a molecular weight in excess of 150 x 10^6. Most of the 100s fragments were retained on the gel to give an estimated size range of 4 x 10^6 to 150 x 10^6 daltons, with the most prominent population estimated to be 4 x 10^6 to 6 x 10^6 daltons.
The free amino group concentration was 700 nM/mg for 100s60 and 480 nM/mg for the 100p60 fraction. The concentration of reducing groups, such as glucose, was 11.5 ug/mg for 100s60 and 9.4 ug/mg for the 100p60 fraction.
The smallest fragments (100s) produced the most severe acute inflammation, but relatively less of the late, recurrent, chronic joint disease. In contrast, the intermediate-sized fragments (100p) produced moderate acute inflammation, but the most severe chronic, degenerative disease.
The outstanding features of this cell wall structure are the toxicity and capacity to invoke dysfunction of the immune system, combined with resistance to biodegradation. PG in aqueous suspension could induce acute injury but not chronic inflammatory disease. Larger fragments, with an average molecular weight of 500 x 10^6, induced a minimal early phase but did induce a chronic arthritis of late onset. Intermediate-size fragments, with a molecular weight of approximately 50 x 10^6 (by light scattering), induced both acute and chronic phases of the disease.
The fragment size is a reflection of the length of glycan polymers (measured as reducing sugar) and the extent of peptide cross-linking (measured as free amino groups). The larger number of free peptide side chains in the 100s fragments, indicated by the higher concentration of free amino groups, could be important in initiating acute inflammation. Less effective degradation of bacterial cells results in the accumulation of sufficient quantities of toxic persistent debris, with the consequent development of chronic inflammation.