Radioimmunoassay system using a serovar-specific lipopolysaccharide antigen of Leptospira

The serovar-specific main (TM) antigen of Leptospira interrogans serovar kremastos strain Kyoto was labeled with sodium boro[3H]hydride after 1 h of oxidation with periodate. When 50 ng of the labeled compound was employed, 50% of the compound was bound to the antibodies contained in 7.5 x 10(-2) nl of anti-kremastos Kyoto serum. Under this condition, only 9 ng of the homologous TM antigen was required for 50% inhibition of serovar kremastos Kyoto 3H-TM antigen-anti-kremastos Kyoto serum binding, whereas 5,000 times as much TM antigen of serovar hebdomadis, which belongs to the same Hebdomadis serogroup as serovar kremastos, was required for the same inhibition. The TM antigens from serovars pomona, icterohaemorrhagiae, and copenhageni, which belong to different serogroups, showed no inhibition in an amount of up to 3 x 10(3), 2 x 10(5), and 2 x 10(5) ng, respectively. In the inhibition study using the serovar hebdomadis TM antigen, inhibition values slightly fluctuated due to the antigen's insolubility. When the TM antigens were solubilized with 0.1% sodium taurodeoxycholate, the fluctuation in inhibition values was minimized, and the cross-reactivity of the serovar hebdomadis TM antigen with anti-kremastos Kyoto serum was diminished, while the inhibitory activity of the serovar kremastos Kyoto TM antigen was enhanced.