A: Reversion of angiostatin angiogenesis inhibition by function blocking antibodies to IL-12. The matrigel angiogenesis assay was performed with the addition of factors as indicated by "+". The angiogenic stimulant was either Kaposi's sarcoma cell conditioned medium (KSCM) or VEGF (100 ng/ml) and TNFα (2 ng/ml) as indicated. AST = addition of angiostatin at 2.5 μg/ml. Anti-IL-12 = addition of 150 ng/ml of anti-IL12 antibodies. Means ± SEM are shown. *** = P < 0.001 (Mann-Whitney) when compared to controls (VEGF/TNFα or KSCM). N = indicates the number of samples in each group. Irrelevant antibodies had little effect on angiogenesis or AST inhibition (data not shown). B: Serum levels of IL-12 found in mice following weekly treatment with angiostatin. *** = P < 0.001 (Mann-Whitney) when compared to control. C: Histology of matrigel sponges. Gels removed at the end of the angiogenesis assay were fixed and paraffin embedded, 4 μM sections were obtained and hematoxylin-eosin stained. Addition of an angiogenic stimulus (KSCM shown) resulted in cellular infiltration and vascularization of the matrigel. The addition of AST strongly inhibited both cellular infiltration and angiogenesis. Antibodies to IL-12 (anti-IL-12) reversed the inhibitory effect of AST on cellular infiltration and vessel formation, but had little effect in control gels. Bar = 200 μm.