Fractions from the conA–Sepharose affinity (each at 10% vol/vol), Sepharose Q anion exchange (A1 at 15% vol/vol; GF at 10% vol/vol), S-200 gel filtration (each at 15% vol/vol), and IgM affinity (each at 15% vol/vol) columns were examined for their ability to support rosette formation when used in combination in the rosetting assay, as described in the legend to Figure 1. The relative percentage rosetting is the average of 2 separate experiments, each using a different batch of fractions from each column. The average rosette size was determined by counting the number of uninfected RBC in at least 100 rosettes per sample on one batch of fractions from each column. + denotes significant difference compared with the size of rosettes formed in whole serum (P = 0.05). The fractions tested were as described in the legend to Table 1.