Using CHO cells expressing full length CC1 or CC1(Q89N), the ability of the soluble native (CC1-Fc) or CC1(Q89N)-Fc to inhibit bacterial binding was assessed using C751 OpaB bacteria (Fig. 9 ). Data show the following: (i) Binding to CHO cells as reported previously (Virji et al., 1996b) was observed only with Opa+ and not Opa-bacteria and no binding was seen with untransfected cells (not shown), (ii) Despite the low levels of binding of the isolate to the soluble CC1 construct carrying the Q89N mutation in the dot immunoblot analysis (Fig. 3B) , bacterial binding to the receptor expressed on the cells was clearly visible (Fig. 9D) , (iii) As in the case of THi Rd described above, association was only significantly high with cells expressing high levels of the receptor (assessed in parallel experiments, not shown), (iv) CC1-Fc could compete with bacterial binding to the homologous native structure expressed on CHO cells (Fig. 9B) , confirming previous results (Virji et al., 1996b) , (v) In comparison, CC1-Fc could more efficiently compete out C751 OpaB binding to the CC1(Q89N) receptor expressed on CHO cells (Fig. 9E) , consistent with its higher affinity for the isolate than CC1(Q89N)-Fc (Fig. 3B) , (vi) CC1(Q89N)-Fc construct was largely ineffective in competing with either cell-expressed receptor ( Fig. 9C and F) ent bacterial numbers are thus also low (cf. Fig. 9D and F: lack of low level binding in F compared with D). The data emphasize the importance of cell presentation of receptor in addition to receptor structure in bacterial interactions.