Immunological and morphological analysis of sodium dodecyl sulfate extract of Leptospira

Sodium dodecyl sulfate (SDS) extract of Leptospira interrogans serotype icterohaemorrhagiae strain Shibaura was fractionated by rate zonal centrifugation in sucrose density gradient, and the fractions were analysed immunologically and morphologically. Two main peaks of antigenic activities were obtained. The first peak showed activities of strong indirect hemagglutination (IHA), weak complement fixation (CF), and low production of agglutinin in mice, and produced 5 precipitin lines in immunodiffusion with homologous strain antiserum. It gave only partial protection to guinea pigs. No recognizable structural components were found electron microscopically in the first peak. The second peak, on the other hand, showed no IHA activity, strong CF activity, high production of agglutinin in mice, and produced no precipitin line in immunodiffusion. It gave complete protection to guinea pigs. Membrane fragments of the enveloping sheath were found electron microscopically in the second peak. The protective activity of SDS extract of leptospira was thus intimately associated with the activityes of agglutinin production and CF, as well as with the membranous structures of the enveloping sheath.