Autoimmune hemolytic anemia by coexisting anti-I and anti-Fl cold agglutinins

Clearance of pathological antibodies using biomimetic nanoparticles

Pathological antibodies have been demonstrated to play a key role in type II immune hypersensitivity reactions, resulting in the destruction of healthy tissues and leading to considerable morbidity for the patient. Unfortunately, current treatments present significant iatrogenic risk while still falling short for many patients in achieving clinical remission. In the present work, we explored the capability of target cell membrane-coated nanoparticles to abrogate the effect of pathological antibodies in an effort to minimize disease burden, without the need for drug-based immune suppression. Inspired by antibody-driven pathology, we used intact RBC membranes stabilized by biodegradable polymeric nanoparticle cores to serve as an alternative target for pathological antibodies in an antibody-induced anemia disease model. Through both in vitro and in vivo studies, we demonstrated efficacy of RBC membrane-cloaked nanoparticles to bind and neutralize anti-RBC polyclonal IgG effectively, and thus preserve circulating RBCs.

Cold agglutination

Autoantibodies against red cells optimally reacting at 0 degree C, ie, CA, are normally found with low titers in the serum of human adults. High-titer CA may be induced by certain infectious agents, including M pneumoniae, EBV, CMV, and rubella virus, or may develop on the basis of chronic (malignant) B cell lymphoproliferation. The main clinical manifestation of cold agglutination is AIHA. Antigens and antibodies of cold agglutination are the best characterized reaction partners of a human autoimmune process. CA may recognize I and i antigens, which are lipid- and protein-linked branched and linear N-acetyl-lactosamine chains, respectively. They are precursors of the ABH blood group antigens and are converted into H by fucosylation. An alternative substitution by sialylation creates Gd, Fl, and probably Vo/Li antigens. CA with anti-Pr and anti-Sa specificities recognize 0-glycans with immunodominant sialyl groups on glycophorins. Several Pr subspecificities can be identified by chemically modified sialyl groups on glycophorins. Because CA in chronic lymphoproliferation are monoclonal antibodies, structure-specificity-interrelations of the antibodies could be identified by primary structure analyses of the N-terminal variable regions of H and L chains and by studies on CA idiotypes. Interrelations between distinct CA specificities and particular infectious agents could explain cold agglutination as a response to receptors for the agents or to the binding sites of antibodies against the agents. Interrelations also existing between certain CA isotypes (Ig classes and L chain types) and CA specificities could be a basis for the elucidation of the enigmatic etiology of chronic (malignant) monoclonal cold agglutination.

Coexisting anti-I and anti-F1/Gd cold agglutinins in infections by Mycoplasma pneumoniae

192 sera containing cold agglutinins of apparent anti-I specificity were reinvestigated for concomitant cold agglutinins (CA) against sialic acid-dependent antigens. 35 cases of additional anti-F1 and 3 cases of additional anti-Gd were detected. 53% of cases with coexisting anti-I and anti-F1/Gd CA had a clinical diagnosis of pneumonia, in 39% IgM antibodies against Mycoplasma pneumoniae could be demonstrated. Since F1 and Gd antigens are identical with the structures identified as receptors for M. pneumoniae, the findings support the hypothesis that postinfectious CA are directed against the receptor of the infectious agent.