Role of heat labile antigens of Shigella flexneri in hela cell invasion

In studies of the role of surface antigens of Shigella flexneri in HeLa cell invasion, three antisera were employed to block the invasion. Antisera against live (ALS) and boiled (ABS) S. flexneri blocked invasion very effectively. Reduction in the numbers of intracellular shigellae was always accompanied by reduction in the number adherent to the cells, indicating the importance of adhesion in the invasive process. Anti-live absorbed antiserum (ALAS) prepared by exhaustive absorption of ALS with boiled S. flexneri blocked adhesion and invasion at dilutions of 20 or 50; the efficiency of the absorption was indicated by absence of agglutinating and anti-lipopolysaccharide (LPS) antibodies. S. flexneri LPS did not block adhesion and invasion even at a concentration of 1.0 mg/ml. Hence it was concluded that heat-labile surface antigens are important in adhesion and invasion of HeLa cells by S. flexneri. Antiserum against heat stable antigen (ABS) probably blocks adhesion by steric hindrance.