Protective effect of Plantago major L. pectin polysaccharide against systemic Streptococcus pneumoniae infection in mice

The antibacterial effect of a soluble pectin polysaccharide, PMII, isolated from the leaves of Plantago major, was examined in inbred NIH/OlaHsd and F ox Chase SCID mice experimentally infected with Streptococcus pneumoniae se rotype 6B. Serotype 6B is known to give a more protracted infection when in jected intraperitoneally into susceptible mice than more virulent serotypes like type 4. PMII was administered i.p. either once 3 days before challeng e or once to thrice from 3 to 48 h after challenge. The number of bacteria in blood and the mouse survival rate were recorded. Pre-challenge administr ation of PMII and also lipopolysaccharide (LPS), included as a control, gav e a dose-dependent protective effect against S. pneumoniae type 6B infectio n. However, injection of PMII after establishment of the infection in NIH/O laHsd mice had no effect. The data demonstrate that, firstly, the polysacch aride fraction PMII from P. major protects against pneumococcal infection i n mice when administered systemically prechallenge, and secondly that the p rotective effect is owing to stimulation of the innate and not the adaptive immune system.