Correlation of TB activity and antibody units of rabbit anti-Pfs25 sera. Groups of 4 rabbits were immunized with 80 μg of Pfs25 as described in the legend to Figure 2. Individual and pooled sera were diluted 1:2 and 1:8, and then tested for TB activity in mosquito membrane feeding assays using sexual stages of P. falciparum and A. stephensi mosquitoes. Anti-Pfs25 antibody units of each sample prior to dilution were determined by ELISA. Antibody unit values for the diluted sera are plotted on the X-axis and % inhibition of oocyst density per mosquito (open triangles) of the same sample or % inhibition of infected mosquitoes (closed circles) of the same sample is plotted on the Y-axis. There is a strong correlation between the antibody units and % inhibition of oocyst density per mosquito or % inhibition of infected mosquitoes (the Spearman Rank Correlations are 0.934 and 0.900, respectively). Lines represent regression of result by use of a hyperbolic equation: Solid line – correlation between antibody units and % inhibition of oocyst density per mosquito; broken line – correlation between antibody units and % inhibition of infected mosquitoes.