To determine both the specificity and affinity of the selected antibodies, ELISA with both Fab and IgG formats were conducted as described in the methods. All Fabs and IgGs bound to their respective antigens specifically without cross-reaction to other antigens tested (Figure 1b and d) . Anti-F1 Fab and IgG have apparent affinities in the low and sub-nM range, respectively. Both m253 and m254 Fabs have apparent affinities of approximately 100 nM (Figure 1b and d) . Their IgGs however have sub-nM apparent affinities (avidities). The avidity effect is very pronounced for all three antibodies.