The effect of silica treatment (5 mg intravenously) on tumour growth was studied with regard to three types of immunosuppression induced by: lentil lectin (LCA), spleen cell extract (SE) (active enhancement), and alloantiserum (AAS) (passive enhancement). Two experimental tumours were used, which differ in their sensitivity to humoral antibodies. CBA mice were challenged with Sa 1 (A) tumours and BALB/c mice with EL-4 (C57BL/6) lymphomas. The results indicate that silica treatment caused a time-dependent promotion of tumour growth. In passive enhancement, tumour growth promotion by silica treatment was obtained in both tumour systems. When silica was given along with LCA or SE, the two combined treatments had no enhancing effect on Sa 1 targets and enhancing effects on EL-4. The different behaviour of the two graft-recipient combinations is discussed in the light of the inherent properties of both experimental tumours and of the donor-recipient relationships.

Institute of Molecular Genetics Czechoslovak Academy of Sciences Praha