Neisseria gonorrhoeae strain MS11 is able to express 11 different opacity (Opa) proteins on its outer surface. A number of these Opa proteins have been shown to function as adhesins through binding of CD66 receptors present on human cells. CD66 antigens, or carcinoembryonic antigen family members, constitute a family of glycoproteins belonging to the immunoglobulin superfamily. Opa variants recognize this class of receptors in a differential manner such that certain Opa variants recognize up to four different CD66 receptors (CD66a, -c, -d, and -e), whereas others recognize only two (CD66a and -e) or none. We explored the basis for this receptor tropism in the present study. Our data show that glycoforms of CD66e and deglycosylated CD66e are recognized by gonococci in an Opa-specific manner. Binding by Opa variants of recombinant N-terminal domains of CD66 receptors expressed in Escherichia coli reflected the adherence specificities of Opa variants to HeLa cells expressing native CD66 molecules. These data indicate that recognition of CD66 receptors by Opa variants is mediated by the protein backbone of the CD66 N-domains. Furthermore, by using chimeric constructs between different CD66 N-domains we identified distinct binding regions on the CD66e N-domain for specific groups of Opa variants, suggesting that the differential recognition of CD66 receptors by Opa variants is dictated by the presence of specific binding regions on the N-domain of the receptor.

Well-characterized mouse models of alloimmune antibody-mediated hemolysis would provide a valuable approach for gaining greater insight into the pathophysiology of hemolytic transfusion reactions. To this end, mouse red blood cells (mRBCs) from human glycophorin A transgenic (hGPA-Tg) donor mice were transfused into non-Tg recipients that had been passively immunized with IgG or IgM hGPA-specific monoclonal antibodies (mAbs). In this novel murine "blood group system," mRBCs from hGPA-Tg IntroductionHemolytic transfusion reactions (HTRs) are dangerous complications of blood transfusions. IgM-mediated HTRs (IgM-HTRs) occur acutely, are usually due to ABO incompatibility, typically cause intravascular hemolysis, and can lead to shock, renal failure, coagulopathy, and death. 1 Although infrequent, IgM-HTRs have a high mortality rate. IgG-mediated HTRs (IgG-HTRs) are more common, but usually less severe, than IgM-HTRs; they can occur acutely or be delayed, typically cause extravascular hemolysis, and occasionally result in renal failure, coagulopathy, and death. 2 Symptomatic immune-mediated red blood cell (RBC) destruction also occurs in autoimmune hemolytic anemia (AIHA), 3 blood group incompatible transplantation, 4 and immune thrombocytopenic purpura (ITP) treated with Rh-immune globulin. 5 Although various different modalities are used to treat HTRs, there is no definitive evidence regarding efficacy. Given the sporadic nature of HTRs, designing human trials to evaluate treatment options is difficult. Therefore, to study the mechanisms underlying HTRs, to evaluate the efficacy of existing treatments, and to develop new treatments, a relevant, inexpensive, and tractable animal model is required. 6 A mouse model would be ideal for this purpose, 7 given the abundance of reagents and relevant knockout (KO) and transgenic (Tg) animals. Although mouse blood group polymorphisms exist, 8 and transfused incompatible mouse RBC (mRBCs) are rapidly cleared, 9,10 no one has exploited these findings to develop a model of HTRs. The availability of a Tg mouse expressing human glycophorin A (hGPA; gene symbol designation, GYPA) on mRBCs 11 offers an approach using a well-described glycoprotein target and well-characterized reagents.We describe initial studies validating mouse models of IgG-and IgM-mediated alloimmune hemolysis. Thus, mRBCs from hGPA-Tg donors were transfused into non-Tg recipients that were passively immunized with IgG or IgM hGPA-specific monoclonal antibodies (mAbs). The clearance of the transfused mRBCs was quantified and the roles of complement and Fc␥ receptors were evaluated. Materials and methods AntibodiesPurified mAbs NaM10-2H12 (IgG3), NaM26-3F4 (IgG1), and NaM10-6G4 (IgG2a), which recognize peptide epitopes on the M and N forms of hGPA, 12 were purchased from EFS (Nantes, France). Hybridomas producing mAb 6A7, an IgG1 specific for a sialic acid-dependent epitope on M-type hGPA, 13-15 10F7, an IgG1 recognizing a nonpolymorphic epitope on hGPA, 13,14 and J11d, a rat IgM recognizing CD24 on mRBCs, 16,17...

Light-chain shuffling allowed the isolation of bacterially produced, high-affinity, soluble, monovalent recombinant anti-N Fab fragments that functioned well by agglutination. This approach is useful in obtaining inexpensive serologic reagents that may replace conventional MoAbs produced by tissue culture methods.

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